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To better understand neural processing during adaptive learning of stimulus‐response‐reward contingencies, we recorded synchrony of neuronal activity in anterior cingulate cortex (ACC) and hippocampal rhythms in male rats acquiring and switching between spatial and visual discrimination tasks in a Y‐maze. ACC population activity as well as single unit activity shifted shortly after task rule changes or just before the rats adopted different task strategies. Hippocampal theta oscillations (associated with memory encoding) modulated an elevated proportion of rule‐change responsive neurons (70%), but other neurons that were correlated with strategy‐change, strategy value and reward‐rate were not. However, hippocampal sharp wave‐ripples modulated significantly higher proportions of rule‐change, strategy‐change and reward‐rate responsive cells during post‐session sleep but not pre‐session sleep. This suggests an underestimated mechanism for hippocampal mismatch and contextual signals to facilitate ACC to detect contingency changes for cognitive flexibility, a function that is attenuated after it is damaged. [ABSTRACT FROM AUTHOR]

This article explores the complexities of the brain's cholinergic systems and the need to revise long-held theories about their function. It discusses the role of cholinergic regulation in various diseases and highlights new research on its modulation across diverse networks and behaviors. The article emphasizes the importance of understanding the spatiotemporal dynamics of cholinergic signaling in the hippocampus for the development of treatments for cognitive impairments and neuropsychiatric disorders. The authors also discuss the role of α7 nicotinic receptors in memory processing, the expression of different nAChR subunit transcripts in specific cell types in the brain, and the importance of cholinergic signaling in mood regulation, motor control, and migraines. They stress the need for further research to understand the unique circuits and functions regulated by cholinergic signaling and to develop targeted therapeutics. [Extracted from the article]

Resting state electroencephalographic (EEG) activity in schizophrenia (SZ) is frequently characterised by increased power at slow frequencies and/or a reduction of peak alpha frequency. Here we investigated the nature of these effects. As most studies to date have been limited by reliance on a priori frequency bands which impose an assumed structure on the data, we performed a data‐driven analysis of resting EEG recorded in SZ patients and healthy controls (HC). The sample consisted of 39 chronic SZ and 36 matched HC. The EEG was recorded with a dense electrode array. Power spectral densities were decomposed via Varimax‐rotated principal component analysis (PCA) over all participants and for each group separately. Spectral PCA was repeated at the cortical level on cortical current source density computed from standardised low resolution brain electromagnetic tomography. There was a trend for power in the theta/alpha range to be increased in SZ compared to HC, and peak alpha frequency was significantly reduced in SZ. PCA revealed that this frequency shift was because of the presence of a spectral component in the theta/alpha range (6–9 Hz) that was unique to SZ. The source distribution of the SZ > HC theta/alpha effect involved mainly prefrontal and parahippocampal areas. Abnormal low frequency resting EEG activity in SZ was accounted for by a unique theta/alpha oscillation. Other reports have described a similar phenomenon suggesting that the neural circuits oscillating in this range are relevant to SZ pathophysiology. [ABSTRACT FROM AUTHOR]

Neuroimaging resting state paradigms have revealed synchronised oscillatory activity is present even in the absence of completing a task or mental operation. One function of this neural activity is likely to optimise the brain's sensitivity to forthcoming information that, in turn, likely promotes subsequent learning and memory outcomes. The current study investigated whether this extends to implicit forms of learning. A total of 85 healthy adults participated in the study. Resting state electroencephalography was first acquired from participants before they completed a serial reaction time task. On this task, participants implicitly learnt a visuospatial‐motor sequence. Permutation testing revealed a negative correlation between implicit sequence learning and resting state power in the upper theta band (6–7 Hz). That is, lower levels of resting state power in this frequency range were associated with superior levels of implicit sequence learning. This association was observed at midline‐frontal, right‐frontal and left‐posterior electrodes. Oscillatory activity in the upper theta band supports a range of top‐down processes including attention, inhibitory control and working memory, perhaps just for visuospatial information. Our results may be indicating that disengaging theta‐supported top‐down attentional processes improves implicit learning of visuospatial‐motor information that is embedded in sensory input. This may occur because the brain's sensitivity to this type of information is optimally achieved when learning is driven by bottom‐up processes. Moreover, the results of this study further demonstrate that resting state synchronised brain activity influences subsequent learning and memory. [ABSTRACT FROM AUTHOR]

Supplementing an earlier analysis of event‐related potentials in extensive motor learning (Margraf et al., 2022a, 2022b), frontal theta‐band activity (4–8 Hz) was scrutinized. Thirty‐seven participants learned a sequential arm movement with 192 trials in each of five practice sessions. Feedback, based on a performance adaptive bandwidth, was given after every trial. Electroencephalogram (EEG) was recorded in the first and last practice sessions. The degree of motor automatization was tested under dual‐task conditions in a pre‐test–post‐test design. Quantitative error information was transported in both feedback conditions (positive and negative). Frontal theta activity was discussed as a general signal that cognitive control is needed and, therefore, was expected to be higher after negative feedback. Extensive motor practice promotes automatization, and therefore, decreased frontal theta activity was expected in the later practice. Further, it was expected that frontal theta was predictive for subsequent behavioural adaptations and the amount of motor automatization. As the results show, induced frontal theta power was higher after negative feedback and decreased after five sessions of practice. Moreover, induced theta activity was predictive for error correction and, therefore, an indicator of whether the recruited cognitive resources successfully induced behavioural adaptations. It remains to be solved why these effects, which fit well with the theoretical assumptions, were only revealed by the induced part of frontal theta activity. Further, the amount of theta activity during practice was not predictive for the degree of motor automatization. It seems that there might be a dissociation between attentional resources associated with feedback processing and attentional resources associated with motor control. [ABSTRACT FROM AUTHOR]

Type 2 diabetes mellitus (T2DM) increases the risk of developing Alzheimer's disease (AD), which has been proposed to be driven by an abnormal neuroinflammatory response affecting cognitive function. However, the impact of T2DM on hippocampal function and synaptic integrity during aging has not been investigated. Here, we investigated the effects of aging in T2DM on AD‐like pathology using the leptin receptor‐deficient db/db mouse model of T2DM. Our results indicate that adult T2DM mice exhibited impaired spatial acquisition in the Morris water maze (MWM). Morphological analysis showed an age‐dependent neuronal loss in the dentate gyrus. We found that astrocyte density was significantly decreased in all regions of the hippocampus in T2DM mice. Our analysis showed that microglial activation was increased in the CA3 and the dentate gyrus of the hippocampus in an age‐dependent manner in T2DM mice. However, the expression of presynaptic marker protein (synaptophysin) and the postsynaptic marker protein [postsynaptic density protein 95 (PSD95)] was unchanged in the hippocampus of adult T2DM mice. Interestingly, synaptophysin and PSD95 expression significantly decreased in the hippocampus of aged T2DM mice, suggesting an impaired hippocampal synaptic integrity. Cytokine profiling analysis displayed a robust pro‐inflammatory cytokine profile in the hippocampus of aged T2DM mice compared with the younger cohort, outlining the role of aging in exacerbating the neuroinflammatory profile in the diabetic state. Our results suggest that T2DM impairs cognitive function by promoting neuronal loss in the dentate gyrus and triggering an age‐dependent deterioration in hippocampal synaptic integrity, associated with an aberrant neuroinflammatory response. [ABSTRACT FROM AUTHOR]

Attentional blink (AB) is the impaired detection of a second target (T2) after a first target has been identified. In this paper, we investigated the functional roles of alpha and theta oscillations on AB by determining how much preceding rhythmic auditory stimulation affected the performance of AB. Healthy young adults participated in the experiment online. We found that when two targets were embedded in rapid serial visual presentation (RSVP) of distractors at 10 Hz (i.e., alpha frequency), the magnitude of AB increased with auditory stimuli. The increase was limited to the case when the frequency and phase of auditory stimuli matched the following RSVP stream. On the contrary, when only two targets were presented without distractors, auditory stimuli at theta, not alpha, increased the AB magnitude. These results indicate that neural oscillations at two different frequencies, namely, alpha and theta, are involved in attentional blink. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests that visual perception operates in an oscillatory fashion at an alpha frequency (around 10 Hz). Moreover, visual attention also seems to operate rhythmically, albeit at a theta frequency (around 5 Hz). Both rhythms are often associated to "perceptual snapshots" taken at the favorable phases of these rhythms. However, less is known about the unfavorable phases: do they constitute "blind gaps," requiring the observer to guess, or is information sampled with reduced precision insufficient for the task demands? As simple detection or discrimination tasks cannot distinguish these options, we applied a continuous report task by asking for the exact orientation of a Landolt ring's gap to estimate separate model parameters for precision and the amount of guessing. We embedded this task in a well‐established psychophysical protocol by densely sampling such reports across 20 cue‐target stimulus onset asynchronies in a Posner‐like cueing paradigm manipulating involuntary spatial attention. Testing the resulting time courses of the guessing and precision parameters for rhythmicities using a fast Fourier transform, we found an alpha rhythm (9.6 Hz) in precision for invalidly cued trials and a theta rhythm (4.8 Hz) in the guess rate across validity conditions. These results suggest distinct roles of the perceptual alpha and the attentional theta rhythm. We speculate that both rhythms result in environmental sampling characterized by fluctuating spatial resolution, speaking against a strict succession of blind gaps and perceptual snapshots. [ABSTRACT FROM AUTHOR]

To maintain a continuous and coherent percept over time, the brain makes use of past sensory information to anticipate forthcoming stimuli. We recently showed that auditory experience of the immediate past is propagated through ear‐specific reverberations, manifested as rhythmic fluctuations of decision bias at alpha frequencies. Here, we apply the same time‐resolved behavioural method to investigate how perceptual performance changes over time under conditions of stimulus expectation and to examine the effect of unexpected events on behaviour. As in our previous study, participants were required to discriminate the ear‐of‐origin of a brief monaural pure tone embedded in uncorrelated dichotic white noise. We manipulated stimulus expectation by increasing the target probability in one ear to 80%. Consistent with our earlier findings, performance did not remain constant across trials, but varied rhythmically with delay from noise onset. Specifically, decision bias showed a similar oscillation at ~9 Hz, which depended on ear congruency between successive targets. This suggests rhythmic communication of auditory perceptual history occurs early and is not readily influenced by top‐down expectations. In addition, we report a novel observation specific to infrequent, unexpected stimuli that gave rise to oscillations in accuracy at ~7.6 Hz one trial after the target occurred in the non‐anticipated ear. This new behavioural oscillation may reflect a mechanism for updating the sensory representation once a prediction error has been detected. [ABSTRACT FROM AUTHOR]

Attentional processes allow the brain to overcome its processing capacities limitations by enhancing relevant visual information and suppressing irrelevant information. Thus attention plays a critical role, shaping our perception of the world. Several models have been proposed to describe the neuronal bases of attention and its mechanistic underlyings. Recent electrophysiological evidence show that attentional processes rely on oscillatory brain activities that correlate with rhythmic changes in cognitive performance. In the present review, we first take a historical perspective on how attention is viewed, from the initial spotlight theory of attention to the recent dynamic view of attention selection and we review their supporting psychophysical evidence. Based on recent prefrontal electrophysiological evidence, we refine the most recent models of attention sampling by proposing a rhythmic and continuous model of attentional sampling. In particular, we show that attention involves a continuous exploration of space, shifting within and across visual hemifield at specific alpha and theta rhythms, independently of the current attentional load. In addition, we show that this prefrontal attentional spotlight implements conjointly selection and suppression mechanisms, and is captured by salient incoming items. Last, we argue that this attention spotlight implements a highly flexible alternation of attentional exploration and exploitation epochs, depending on ongoing task contingencies. In a last part, we review the local and network oscillatory mechanisms that correlate with rhythmic attentional sampling, describing multiple rhythmic generators and complex network interactions. [ABSTRACT FROM AUTHOR]

The goal of this study was to determine whether the cortical responses elicited by whole‐body balance perturbations were similar to established cortical markers of action monitoring. Postural changes imposed by balance perturbations elicit a robust negative potential (N1) and a brisk increase of theta activity in the electroencephalogram recorded over midfrontal scalp areas. Because action monitoring is a cognitive function proposed to detect errors and initiate corrective adjustments, we hypothesized that the possible cortical markers of action monitoring during balance control (N1 potential and theta rhythm) scale with perturbation intensity and the eventual execution of reactive stepping responses (as opposed to feet‐in‐place responses). We recorded high‐density electroencephalogram from eleven young individuals, who participated in an experimental balance assessment. The participants were asked to recover balance following anteroposterior translations of the support surface at various intensities, while attempting to maintain both feet in place. We estimated source‐resolved cortical activity using independent component analysis. Combining time‐frequency decomposition and group‐level general linear modeling of single‐trial responses, we found a significant relation of the interaction between perturbation intensity and stepping responses with multiple cortical features from the midfrontal cortex, including the N1 potential, and theta, alpha, and beta rhythms. Our findings suggest that the cortical responses to balance perturbations index the magnitude of a deviation from a stable postural state to predict the need for reactive stepping responses. We propose that the cortical control of balance may involve cognitive control mechanisms (i.e., action monitoring) that facilitate postural adjustments to maintain postural stability. [ABSTRACT FROM AUTHOR]

Modification of ongoing walking movement to fit changes in external environments requires accurate voluntary control. In cats, the motor and posterior parietal cortices have crucial roles for precisely adjusting limb trajectory during walking. In human walking, however, it remains unclear which cortical information contributes to voluntary gait modification. In this study, we investigated cortical activity changes associated with visually guided precision stepping using electroencephalography source analysis. Our results demonstrated frequency‐ and gait‐event‐dependent changes in the cortical power spectrum elicited by voluntary gait modification. The main differences between normal walking and precision stepping were as follows: (a) the alpha, beta or gamma power decrease during the swing phases in the sensorimotor, anterior cingulate and parieto‐occipital cortices, and (b) a power decrease in the theta, alpha and beta bands and increase in the gamma band throughout the gait cycle in the parieto‐occipital cortex. Based on the previous knowledge of brain functions, the former change was considered to be related to execution and planning of leg movement, while the latter change was considered to be related to multisensory integration and motor awareness. Therefore, our results suggest that the gait modification is achieved by higher cortical involvements associated with different sensorimotor‐related functions across multiple cortical regions including the sensorimotor, anterior cingulate and parieto‐occipital cortices. The results imply the critical importance of the cortical contribution to voluntary modification in human locomotion. Further, the observed cortical information related to voluntary gait modification would contribute to developing volitional control systems of brain–machine interfaces for walking rehabilitation. [ABSTRACT FROM AUTHOR]

For a long time, mice have been classified as adults with completely mature brains at 8 weeks of age, but recent research suggests that developmental brain changes occur for up to 6 months. In particular, adolescence coincides with dramatic changes of neuronal structure and function in the brain that influence the connectivity between areas like hippocampus and medial prefrontal cortex (mPFC). Neuronal development and plasticity are regulated in part by the palmitoyl acyltransferase ZDHHC7, which modulates structural connectivity between hippocampus and mPFC. The aim of the current study was to investigate whether developmental changes take place in hippocampus and mPFC microstructure even after 8 weeks of age and whether deficiency of ZDHHC7 impacts such age‐dependent alterations. Altogether, 46 mice at 11, 14 or 17 weeks of age with a genetic Zdhhc7 knockout (KO) or wild type (WT) were analysed with neuroimaging and diffusion tensor‐based fibre tractography. The hippocampus and mPFC regions were compared regarding fibre metrics, supplemented by volumetric and immunohistological analyses of the hippocampus. In WT animals, we identified age‐dependent changes in hippocampal fibre lengths that followed a U‐shaped pattern, whereas in mPFC, changes were linear. In Zdhhc7‐deficient animals, the fibre statistics were reduced in both regions, whereas the hippocampus volume and the intensities of myelin and neurofilament were higher in 11‐week‐old KO mice compared to WTs. Our results confirmed ongoing changes of microstructure in mice up to 17 weeks old and demonstrate that deleting the Zdhhc7 gene impairs fibre development, suggesting that palmitoylation is important in this process. [ABSTRACT FROM AUTHOR]

Long‐term potentiation (LTP) is a highly studied cellular process, yet determining the transduction and gamma aminobutyric acid (GABAergic) pathways that are the essential versus modulatory for LTP elicited by theta burst stimulation (TBS) in the hippocampal Cornu Ammonis 1 (CA1) area is still elusive, due to the use of different TBS intensities, patterns or different rodent/cellular models. We now characterised the developmental maturation and the transduction and GABAergic pathways required for mild TBS‐induced LTP in hippocampal CA1 area in male rats. LTP induced by TBS (5x4) (five bursts of four pulses delivered at 100 Hz) lasted for up to 3 h and was increasingly larger from weaning to adulthood. Stronger TBS patterns ‐ TBS (15x4) or three TBS (15x4) separated by 6 min induced nearly maximal LTP not being the best choice to study the value of LTP‐enhancing drugs. LTP induced by TBS (5x4) in young adults was fully dependent on N‐methyl D‐aspartate (NMDA) receptor and calmodulin‐dependent protein kinase II (CaMKII) activity but independent of protein kinase A (PKA) or protein kinase C (PKC) activity. Furthermore, it was partially dependent on GABAB receptor activation and was potentiated by GABAA receptor blockade and less by GAT‐1 transporter blockade. AMPA GluA1 phosphorylation on Ser831 (CaMKII target) but not GluA1 Ser845 (PKA target) was essential for LTP expression. The phosphorylation of the Kv4.2 channel was observed at Ser438 (CaMKII target) but not at Thr602 or Thr607 (ERK/MAPK pathway target). This suggests that cellular kinases like PKA, PKC, or kinases of the ERK/MAPK family although important modulators of TBS (5x4)‐induced LTP may not be essential for its expression in the CA1 area of the hippocampus. [ABSTRACT FROM AUTHOR]

The aim of this work is computationally to correlate the synchronized neuronal activity of basal ganglia and slowing in theta and alpha rhythms in electroencephalogram (EEG) signal in thalamic region in case of dopamine depletion and decrease of synaptic connections. The used network topology is a scale‐free network with constant node degree. The dopamine‐modulated type Izikhevich neuron model is used for modeling the striatal region, consisting of fast‐spiking interneurons, D1 and D2 type dopamine expressing medium spiny neurons. On the other hand, the ordinary Izikhevich neuron model is used in the modeling of extrastriatal basal ganglia (BG) regions where globus pallidus (GP) subregion neurons have also dopamine‐dependent parameters. The thalamic region of the network is mass modeled including inhibitory input from basal ganglia. Depending on the decrease of synaptic connections and dopamine level, the synchronization among basal ganglia neuron populations is investigated. The effect of synaptic delay on synchronization is also considered. It is observed that the decrease of dopamine neurotransmitter and decrease in the number of synaptic connections cause an increased synchronous activity in BG. Also, slowing in theta and alpha bands in thalamus EEG signals is observed. This shows the causal relation between synchronization and power shifting to lower frequency components in the case of neurodegenerative diseases such as Parkinson's disease (PD). [ABSTRACT FROM AUTHOR]

γ‐Aminobutyric acid (GABA) acting through heteropentameric GABAA receptors plays a pivotal role in the sleep‐promoting circuitry. Whereas the role of the different GABAA receptor α‐subunits in sleep regulation and in mediating the effect of benzodiazepines for treatment of insomnia is well‐described, the β‐subunits are less studied. Here we report the first study characterizing sleep in mice lacking the GABAA receptor β1‐subunit (β1−/− mice). We show that β1−/− mice have a distinct and abnormal sleep phenotype characterized by increased delta power in non‐rapid eye movement (NREM) sleep and decreased theta activity in rapid eye movement (REM) sleep compared to β1+/+ mice, without any change in the overall sleep‐wake architecture. From GABAA receptor‐specific autoradiography, it is further demonstrated that functional β1‐subunit‐containing GABAA receptors display the highest binding levels in the hippocampus and frontal cortex. In conclusion, this study suggests that the GABAA receptor β1‐subunit does not play an important role in sleep initiation or maintenance but instead regulates the power spectrum and especially the expression of theta rhythm. This provides new knowledge on the complex role of GABAA receptor subunits in sleep regulation. In addition, β1−/− mice could provide a useful mouse model for future studies of the physiological role of delta and theta rhythms during sleep. [ABSTRACT FROM AUTHOR]

Meditation practice entails moments of distraction dominated by self‐generated thoughts (i.e. mind wandering). Initial studies assessing the neural correlates of mind wandering in the context of meditation practice have identified an important role of theta (4–8 Hz) and alpha (8–14 Hz) neural oscillations. In this study, we use a probe‐caught experience sampling paradigm to assess spectral changes in the theta‐alpha frequency range during mind wandering in the context of breath focus meditation. Electroencephalography (EEG) was measured in 25 novice meditation practitioners during a breath focus task in which they were repeatedly probed to report whether they were focusing on their breath or thinking about something else. Mind wandering episodes were associated with an increase in the amplitude and a decrease in the frequency of theta (4–8 Hz) oscillations. Conversely, alpha oscillations (8–14 Hz) were shown to decrease in amplitude and increase in frequency during mind wandering relative to breath focus. In addition, mind wandering episodes were shown to be accompanied by increased harmonicity and phase synchrony between alpha and theta rhythms. Because similar spectral changes in the theta‐alpha frequency range have been reported during controlled cognitive processes involving memory and executive control, we speculate that mind wandering and controlled processes could share some neurocognitive mechanisms. From a translational perspective, this study indicates that oscillatory activity in the theta‐alpha frequency range could form adequate parameters for developing EEG‐neurofeedback protocols aimed at facilitating the detection of mind wandering during meditation practice. [ABSTRACT FROM AUTHOR]

Mild traumatic brain injury (mTBI) can cause persistent cognitive changes. These cognitive changes may be due to changes in neural communication. Task‐switching is a cognitive control operation that may be susceptible to mTBI and is associated with oscillations in theta (4–7 Hz), alpha (8–13 Hz), and beta (14–30 Hz) ranges. This study aimed to investigate oscillatory power in response to cues indicating a task‐switch after mTBI. Electroencephalogram and behavioral data were collected from 21 participants with a history of two or more concussions (mTBI) and 21 age‐ and gender‐matched controls as they performed a task‐switching paradigm. Participants differentiated whether visual stimuli were red or green, or circles or squares, depending on a cue. The cue changed every few trials with the first trial after a rule change being termed a switch trial. The mTBI group showed significantly less overall accuracy during the task. Over a posterior parietal region, the mTBI group showed more theta desynchronization than the control group from ~300 to ~600 ms post‐cue during switch trials and from ~300 to 400 ms during maintain trials, along with less alpha and beta desynchronization than the control group from ~2,000 to ~2,200 ms post‐cue. In a right parietal region, the mTBI group showed less alpha and beta desynchronization from ~525 to ~775 ms post‐cue. However, there was no condition × group interaction in the behavior or oscillatory results. These oscillatory differences suggest a change in neural communication is present after mTBI that may relate to global changes in task performance. Our project examines how multiple concussions, or mild traumatic brain injuries (mTBI), impact brain oscillations during a task‐switching paradigm. Multiple mTBIs lead to an overall decrease in task‐switching performance revealed through a decrease in switch and maintain trial accuracy combined. The changes in task performance may be related to differences in theta, alpha, and beta desynchronization over posterior brain regions. [ABSTRACT FROM AUTHOR]

Anatomical differences between the medial and lateral septum have associated these nuclei with dissimilar functional roles and behaviours. While the medial septum has been implicated, predominantly, in theta rhythm generation along the septo‐hippocampal axis, the lateral septum has mainly been investigated in the context of septo‐hypothalamic dialogue. Recent advances suggest that medial and lateral septum are more closely functionally related than previously appreciated. Here, we explore the hypothesis that the medial septum mediates ascending septo‐hippocampal theta propagation, while the lateral septum processes a descending hippocampo‐septal and septo‐hypothalamic reinforcement signal that mediates navigation during motivated behaviour. The generation and propagation of theta rhythm are critical for the initiation of exploratory behaviour. Indeed, theta signal processing of medial and lateral septum nuclei may well be involved in the integration of spatial, rewarding and locomotor signals across different brain networks. We review here the structural features, anatomical connectivity and functional properties of the medial and lateral septum. We discuss the heterogeneous anatomy of the lateral septum, which is composed of diverse subregions with distinct ascending and descending projections, and we relate the physiological characteristics of septal nuclei to their functional relationships with the hippocampal formation, the hypothalamus and the brainstem reticular formation during motivated spatial navigation. The review examines the anatomical connectivity and functional properties of the medial and lateral septum in the context of theta oscillations and signal integration. The heterogeneous anatomy of the septal nuclei and their connectivity is linked here to specific behaviours. We discuss the physiological characteristics of septal nuclei to their functional relationships with the hippocampal formation, the hypothalamus and the brainstem reticular formation during motivated spatial navigation. [ABSTRACT FROM AUTHOR]

Recently, a novel type of fast cortical oscillatory activity that occurs between 110 and 160 Hz (high‐frequency oscillations (HFO)) was described. HFO are modulated by the theta rhythm in hippocampus and neocortex during active wakefulness and REM sleep. As theta‐HFO coupling increases during REM, a role for HFO in memory consolidation has been proposed. However, global properties such as the cortex‐wide topographic distribution and the cortico‐cortical coherence remain unknown. In this study, we recorded the electroencephalogram during sleep and wakefulness in the rat and analyzed the spatial extent of the HFO band power and coherence. We confirmed that the HFO amplitude is phase‐locked to theta oscillations and is modified by behavioral states. During active wakefulness, HFO power was relatively higher in the neocortex and olfactory bulb compared to sleep. HFO power decreased during non‐REM and had an intermediate level during REM sleep. Furthermore, coherence was larger during active wakefulness than non‐REM, while REM showed a complex pattern in which coherence increased only in intra and decreased in inter‐hemispheric combination of electrodes. This coherence pattern is different from gamma (30–100 Hz) coherence, which is reduced during REM sleep. This data show an important HFO cortico‐cortical dialog during active wakefulness even when the level of theta comodulation is lower than in REM. In contrast, during REM, this dialog is highly modulated by theta and restricted to intra‐hemispheric medial‐posterior cortical regions. Further studies combining behavior, electrophysiology and new analytical tools are needed to plunge deeper into the functional significance of the HFO. We determined that high‐frequency oscillations (HFO, 110‐160 Hz) of the EEG are modulated by theta during active wakefulness and REM sleep. Furthermore, we showed by means of spectral coherence analysis that while there is a cortico‐cortical HFO dialogue throughout the cortex during wakefulness, this dialogue is restricted to intra‐hemispheric medial‐posterior cortical regions during REM sleep. We also provided evidences that HFO intra‐hemispheric coherence is highly modulated by theta. [ABSTRACT FROM AUTHOR]

Recent studies have probed the role of the parieto‐occipital alpha rhythm (8–12 Hz) in human visual perception through attempts to drive its neural generators. To that end, paradigms have used high‐intensity strictly‐periodic visual stimulation that created strong predictions about future stimulus occurrences and repeatedly demonstrated perceptual consequences in line with an entrainment of parieto‐occipital alpha. Our study, in turn, examined the case of alpha entrainment by non‐predictive low‐intensity quasi‐periodic visual stimulation within theta‐ (4–7 Hz), alpha‐ (8–13 Hz), and beta (14–20 Hz) frequency bands, i.e., a class of stimuli that resemble the temporal characteristics of naturally occurring visual input more closely. We have previously reported substantial neural phase‐locking in EEG recording during all three stimulation conditions. Here, we studied to what extent this phase‐locking reflected an entrainment of intrinsic alpha rhythms in the same dataset. Specifically, we tested whether quasi‐periodic visual stimulation affected several properties of parieto‐occipital alpha generators. Speaking against an entrainment of intrinsic alpha rhythms by non‐predictive low‐intensity quasi‐periodic visual stimulation, we found none of these properties to show differences between stimulation frequency bands. In particular, alpha band generators did not show increased sensitivity to alpha band stimulation and Bayesian inference corroborated evidence against an influence of stimulation frequency. Our results set boundary conditions for when and how to expect effects of entrainment of alpha generators and suggest that the parieto‐occipital alpha rhythm may be more inert to external influences than previously thought. Using EEG we tested whether intrinsic alpha rhythms entrain to quasi‐periodic low‐intensity visual stimulation. Our results speak against a stimulus‐driven alpha entrainment when the quasiperiodicity of the stimulation is task‐irrelevant. [ABSTRACT FROM AUTHOR]

Abstract: Our recent finding of a meditation‐related increase in low‐frequency NREM sleep EEG oscillatory activities peaking in the theta‐alpha range (4–12 Hz) was not predicted. From a consolidated body of research on sleep homeostasis, we would expect a change peaking in slow wave activity (1–4 Hz) following an intense meditation session. Here we compared these changes in sleep with the post‐meditation changes in waking rest scalp power to further characterize their functional significance. High‐density EEG recordings were acquired from 27 long‐term meditators (LTM) on three separate days at baseline and following two 8‐hr sessions of either mindfulness or compassion‐and‐loving‐kindness meditation. Thirty‐one meditation‐naïve participants (MNP) were recorded at the same time points. As a common effect of meditation practice, we found increases in low and fast waking EEG oscillations for LTM only, peaking at eight and 15 Hz respectively, over prefrontal, and left centro‐parietal electrodes. Paralleling our previous findings in sleep, there was no significant difference between meditation styles in LTM as well as no difference between matched sessions in MNP. Meditation‐related changes in wakefulness and NREM sleep were correlated across space and frequency. A significant correlation was found in the EEG low frequencies (<12 Hz). Since the peak of coupling was observed in the theta‐alpha oscillatory range, sleep homeostatic response to meditation practice is not sufficient to explain our findings. Another likely phenomenon into play is a reverberation of meditation‐related processes during subsequent sleep. Future studies should ascertain the interplay between these processes in promoting the beneficial effects of meditation practice. [ABSTRACT FROM AUTHOR]

Abstract: Despite accumulating evidence of inter and intraindividual variability in response to theta burst stimulation, it is widely believed that in therapeutic applications, repeated sessions can have a “build‐up” effect that increases the response over and above that seen in a single session. However, strong evidence for this is lacking. Therefore, we examined whether daily administration of intermittent theta burst stimulation (iTBS) over the primary motor cortex induces cumulative changes in transcranial magnetic stimulation measures of cortical excitability, above the changes induced by sham stimulation. Over five consecutive days, 20 healthy participants received either active iTBS or sham stimulation. Each day, baseline measures of cortical excitability were assessed before and up to 30 min after the intervention. There was no significant difference in the rate of response between iTBS and sham stimulation on any of the 5 days. There was no iTBS specific cumulative increase of corticospinal excitability. The likelihood that an individual would remain a responder from day‐to‐day was low in both groups, implying high within‐subject variability of both active and sham iTBS after‐effects. In contrast, we found a high within‐subject repeatability of resting and active motor threshold, and baseline motor‐evoked potential amplitude. In summary, sham stimulation has similar effect to active iTBS on corticospinal excitability, even when applied repeatedly for 5 days. Our results might be relevant to research and clinical applications of theta burst stimulation protocols. [ABSTRACT FROM AUTHOR]

Abstract: When watching performing arts, a wide and complex network of brain processes emerge. These processes can be shaped by professional expertise. When compared to laymen, dancers have enhanced processes in observation of short dance movement and listening to music. But how do the cortical processes differ in musicians and dancers when watching an audio‐visual dance performance? In our study, we presented the participants long excerpts from the contemporary dance choreography of Carmen. During multimodal movement of a dancer, theta phase synchrony over the fronto‐central electrodes was stronger in dancers when compared to musicians and laymen. In addition, alpha synchrony was decreased in all groups during large rapid movement when compared to nearly motionless parts of the choreography. Our results suggest an enhanced cortical communication in dancers when watching dance and, further, that this enhancement is rather related to multimodal, cognitive and emotional processes than to simple observation of dance movement. [ABSTRACT FROM AUTHOR]

Data obtained in in vitro experiments and urethane anaesthetized animals have revealed that the mechanisms responsible for the generation of hippocampal cholinergic theta rhythm are specifically affected by the administration of broad spectrum gap junctions ( GJs) blocker - carbenoxolone ( CBX). The aim of this study was to examine the effect of GJs modulation on the production of posterior hypothalamic theta. Specifically, we were interested in evaluating whether CBX could attenuate the theta rhythm recorded from the supramammillary nucleus and posterior hypothalamic nuclei, in both in vitro and in vivo preparations. The data we obtained from in vitro and in vivo preparations demonstrated that the administration of CBX did not suppress cholinergically induced theta in posterior hypothalamic area ( PHa) slices nor the theta rhythm observed in the PHa of urethane anaesthetized rats. Moreover, the application of trimethylamine, while very effective in the enhancement of hippocampal theta rhythm, did not produce any changes in theta oscillations observed in either in vitro or in vivo posterior hypothalamic area preparations. These data show that electrical coupling via GJs is not involved in theta rhythm generation in the PHa. Surprisingly, we observed a significant enhancement of theta activity in response to the carbenoxolone administration in both in vitro and in vivo PHa preparations. The theta rhythm enhancement detected in those experiments was attenuated by the application of spironolactone (mineralocorticoid receptors antagonist). We suggest that the observed excitatory effects of CBX on posterior hypothalamic oscillatory activity in the theta band could be mediated by mineralocorticoid receptors. [ABSTRACT FROM AUTHOR]

Neuronal gamma-band synchronization (25-80 Hz) in visual cortex appears sustained and stable during prolonged visual stimulation when investigated with conventional averages across trials. However, recent studies in macaque visual cortex have used single- trial analyses to show that both power and frequency of gamma oscillations exhibit substantial moment-by-moment variation. This has raised the question of whether these apparently random variations might limit the functional role of gamma-band synchronization for neural processing. Here, we studied the moment-by-moment variation in gamma oscillation power and frequency, as well as inter-areal gamma synchronization, by simultaneously recording local field potentials in V1 and V2 of two macaque monkeys. We additionally analyzed electrocorticographic V1 data from a third monkey. Our analyses confirm that gamma-band synchronization is not stationary and sustained but undergoes moment-by-moment variations in power and frequency. However, those variations are neither random and nor a possible obstacle to neural communication. Instead, the gamma power and frequency variations are highly structured, shared between areas and shaped by a microsaccade-related 3-4-Hz theta rhythm. Our findings provide experimental support for the suggestion that cross-frequency coupling might structure and facilitate the information flow between brain regions. [ABSTRACT FROM AUTHOR]

This paper describes the existence of theta-coupled neuronal activity in the nucleus incertus ( NI). Theta rhythm is relevant for cognitive processes such as spatial navigation and memory processing, and can be recorded in a number of structures related to the hippocampal activation including the NI. Strong evidence supports the role of this tegmental nucleus in neural circuits integrating behavioural activation with the hippocampal theta rhythm. Theta oscillations have been recorded in the local field potential of the NI, highly coupled to the hippocampal waves, although no rhythmical activity has been reported in neurons of this nucleus. The present work analyses the neuronal activity in the NI in conditions leading to sustained hippocampal theta in the urethane-anaesthetised rat, in order to test whether such activation elicits a differential firing pattern. Wavelet analysis has been used to better define the neuronal activity already described in the nucleus, i.e., non-rhythmical neurons firing at theta frequency (type I neurons) and fast-firing rhythmical neurons (type II). However, the most remarkable finding was that sustained stimulation activated regular-theta neurons (type III), which were almost silent in baseline conditions and have not previously been reported. Thus, we describe the electrophysiological properties of type III neurons, focusing on their coupling to the hippocampal theta. Their spike rate, regularity and phase locking to the oscillations increased at the beginning of the stimulation, suggesting a role in the activation or reset of the oscillation. Further research is needed to address the specific contribution of these neurons to the entire circuit. [ABSTRACT FROM AUTHOR]

Memory for odour information may result from temporal coupling between the olfactory and hippocampal systems. Respiration defines the frequency of olfactory perception, but how the respiratory rate affects hippocampal oscillations remains poorly understood. The afferent connectivity of the medial septum/diagonal band of Broca complex ( MS/ DB) proposes this region as a crossroads between respiratory and limbic pathways. Here we investigate if the firing rates of septal neurons integrate respiratory rate signals. We demonstrate that approximately 50% of MS/ DB neurons are temporally correlated with sniffing frequency. Moreover, a group of slow-spiking septal neurons are phase-locked to the sniffing cycle. We show that inter-burst intervals of MS/ DB theta cells relate to the sniff rate. Intranasal odour infusion evokes sniff phase preference for the activity of fast-spiking MS/ DB neurons. Concurrently, the infusion augments the correlation between sniffing and limbic theta oscillations. During periods of sniffing-theta correlation, CA1 place cells fired preferentially during the inhalation phase, suggesting the theta cycle as a coherent time frame for central olfactory processing. Furthermore, injection of the GABAergic agonist muscimol into medial septum induces a parallel decrease of sniffing and theta frequencies. Our findings provide experimental evidence that MS/ DB does not merely generate theta rhythm, but actively integrates sensorimotor stimuli that reflect sniffing rate. Such integration may provide temporal oscillatory synchronisation of MS/ DB-innervated limbic structures with the sniffing cycle. [ABSTRACT FROM AUTHOR]

Eyeblink classical conditioning ( EBCC) is a cerebellum-dependent paradigm of associative motor learning, and abnormal EBCC is a neurophysiological indicator of cerebellar dysfunction. We have previously demonstrated impaired EBCC in patients with primary dystonia, but it remains uncertain if this represents actual cerebellar pathology or reflects a functional cerebellar disruption. We examined this further by: (1) studying acquisition and retention of EBCC in a second session in eight patients with cervical dystonia ( CD) who had a first session 7-10 days earlier; and (2) by investigating the potential of continuous theta burst stimulation (c TBS) over the right cerebellar hemisphere to modify a first-ever EBCC session in 11 patients with CD. EBCC data of eight healthy controls previously studied were used for additional between-group comparisons. We observed an improvement of EBCC in a second session in patients with CD, which is in contrast to patients with proven cerebellar pathology who do not show further improvement of EBCC in additional sessions. We also found that cerebellar c TBS paradoxically normalized EBCC in patients with CD, while we previously showed that it disrupts EBCC in healthy volunteers. Combined, these two experiments are in keeping with a functional and reversible disruption of the cerebellum in dystonia, a phenomenon that is probably secondary to either cerebellar compensation or to cerebellar recruitment in the abnormal sensorimotor network. [ABSTRACT FROM AUTHOR]

Alzheimer's disease ( AD) is an age-related neurodegenerative disorder characterized by memory impairments. Brain oscillatory activity is critical for cognitive function and is altered in AD patients. Recent evidence suggests that accumulation of soluble amyloid-beta ( Aβ) induces reorganization of hippocampal networks. However, whether fine changes in network activity might be present at very early stages, before Aβ overproduction, remains to be determined. We therefore assessed whether theta and gamma oscillations and their cross-frequency coupling, which are known to be essential for normal memory function, were precociously altered in the hippocampus. Electrophysiological field potential recordings were performed using complete hippocampal preparations in vitro from young transgenic CRND8 mice, a transgenic mouse model of AD. Our results indicate that a significant proportion of 1-month-old Tg CRND8 mice showed robust alterations of theta-gamma cross-frequency coupling in the principal output region of the hippocampus, the subiculum. In addition we showed that, compared to controls, these mice expressed negligible levels of Aβ. Finally, these network alterations were not due to genetic factors as 15-day-old animals did not exhibit theta-gamma coupling alterations. Thus, initial alterations in hippocampal network activity arise before Aβ accumulation and may represent an early biomarker for AD. [ABSTRACT FROM AUTHOR]

The most spectacular example of oscillations and synchrony which appear in the brain is the rhythmic slow activity (theta) of the limbic cortex. Theta rhythm is the best synchronized electroencephalographic activity that can be recorded from the mammalian brain. Hippocampal formation is considered to be the main structure involved in the generation of this activity. Although detailed studies of the physiology and pharmacology of theta-band oscillations have been carried out since the early 1950s, the first demonstration of atropine-sensitive theta rhythm, recorded in completely deafferented hippocampal slices of a rat, was performed in the second half of the 1980s. Since the discovery of cholinergically induced in vitro theta rhythm recorded from hippocampal formation slices, the central mechanisms underlying theta generation have been successfully studied in in vitro conditions. Most of these experiments were focused on the basic question regarding the similarities between the cholinergically induced theta activity and theta rhythm examined in vivo. The results of numerous in vitro experiments strongly suggest that cholinergically induced theta rhythm recorded in hippocampal slices is a useful analogue of theta observed in intact animals, and could be helpful in searching for the mechanisms of oscillations and synchrony in the central nervous system neuronal networks. The objective of the present review is to discuss the main results of experiments concerning theta oscillations recorded in in vitro conditions. It is our intent to provide, on the basis of these results, the characteristics of essential mechanisms underlying the generation of atropine-sensitive in vitro theta. [ABSTRACT FROM AUTHOR]

Chemotherapy, especially if prolonged, disrupts attention, working memory and speed of processing in humans. Most cancer drugs that cross the blood-brain barrier also decrease adult neurogenesis. Because new neurons are generated in the hippocampus, this decrease may contribute to the deficits in working memory and related thought processes. The neurophysiological mechanisms that underlie these deficits are generally unknown. A possible mediator is hippocampal oscillatory activity within the theta range (3-12 Hz). Theta activity predicts and promotes efficient learning in healthy animals and humans. Here, we hypothesised that chemotherapy disrupts learning via decreases in hippocampal adult neurogenesis and theta activity. Temozolomide was administered to adult male Sprague- Dawley rats in a cyclic manner for several weeks. Treatment was followed by training with different types of eyeblink classical conditioning, a form of associative learning. Chemotherapy reduced both neurogenesis and endogenous theta activity, as well as disrupted learning and related theta-band responses to the conditioned stimulus. The detrimental effects of temozolomide only occurred after several weeks of treatment, and only on a task that requires the association of events across a temporal gap and not during training with temporally overlapping stimuli. Chemotherapy did not disrupt the memory for previously learned associations, a memory independent of (new neurons in) the hippocampus. In conclusion, prolonged systemic chemotherapy is associated with a decrease in hippocampal adult neurogenesis and theta activity that may explain the selective deficits in processes of learning that describe the 'chemobrain'. [ABSTRACT FROM AUTHOR]

Synchronization of neuronal activity in the visual cortex at low (30–70 Hz) and high gamma band frequencies (> 70 Hz) has been associated with distinct visual processes, but mechanisms underlying high-frequency gamma oscillations remain unknown. In rat visual cortex slices, kainate and carbachol induce high-frequency gamma oscillations (fast-γ; peak frequency ∼ 80 Hz at 37°C) that can coexist with low-frequency gamma oscillations (slow-γ; peak frequency ∼ 50 Hz at 37°C) in the same column. Current-source density analysis showed that fast-γ was associated with rhythmic current sink-source sequences in layer III and slow-γ with rhythmic current sink-source sequences in layer V. Fast-γ and slow-γ were not phase-locked. Slow-γ power fluctuations were unrelated to fast-γ power fluctuations, but were modulated by the phase of theta (3–8 Hz) oscillations generated in the deep layers. Fast-γ was spatially less coherent than slow-γ. Fast-γ and slow-γ were dependent on γ-aminobutyric acid (GABA)A receptors, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and gap-junctions, their frequencies were reduced by thiopental and were weakly dependent on cycle amplitude. Fast-γ and slow-γ power were differentially modulated by thiopental and adenosine A1 receptor blockade, and their frequencies were differentially modulated by N-methyl-d-aspartate (NMDA) receptors, GluK1 subunit-containing receptors and persistent sodium currents. Our data indicate that fast-γ and slow-γ both depend on and are paced by recurrent inhibition, but have distinct pharmacological modulation profiles. The independent co-existence of fast-γ and slow-γ allows parallel processing of distinct aspects of vision and visual perception. The visual cortex slice provides a novel in vitro model to study cortical high-frequency gamma oscillations. [ABSTRACT FROM AUTHOR]

It has been suggested that theta rhythm gates the flow of information between the hippocampus and cortex during memory processes. The cholinergic system plays an important role in regulating vigilance states and in generating theta rhythm. This study aims to analyse the effects of the muscarinic agonist pilocarpine (120 and 360 µg, i.c.v.) on hippocampal and frontal cortical theta rhythm during several vigilance states in rats. Pilocarpine injection increased the duration and number of episodes with theta activity, particularly when theta rhythm appeared during waking states in the cortex and hippocampus simultaneously. It seems that the effects of pilocarpine are related to the appearance of cortical theta activity in waking states, and suggest that pilocarpine could modify the transference rate of information from the hippocampus to cortex in rats during wakefulness states, in relation to the postulated effect of cholinergic system modulating memory consolidation. [ABSTRACT FROM AUTHOR]

Human brain oscillatory activity was analysed in the electroencephalographic theta frequency range (4–7 Hz) while subjects executed complex sequential finger movements with varying task difficulty and memory load. Local frontal-midline theta activity was associated with the general level of cognitive demand, with the highest amplitudes in the most demanding condition. Using low-resolution electromagnetic tomography analysis (LORETA), this theta activity was localized in the anterior cingulate gyrus including the cingulate motor area. These results suggest that local theta activity in the anterior cingulate gyrus represents correlates of an attentional system that allocate cognitive resources. In addition, interregional connectivity in the theta frequency range was modulated by memory-related executive functions independently of task difficulty. Connectivity analyses revealed a more distributed long-range network including frontal and parietal cortices during execution of novel compared with well-trained finger movement sequences. Thus, these results are compatible with a model in which theta long-range coupling indicates integration of sensory information into executive control components of complex motor behaviour. [ABSTRACT FROM AUTHOR]

The role of gap junction coupling in the generation of theta rhythms in freely moving cats was investigated in a present study. Two gap junction blockers, carbenoxolone and quinine, were administered intraperitoneally and intrahippocampally; both gap junction blockers abolished or diminished (respectively) hippocampal formation theta. The inhibitory effect developed approximately 30 min after drug administration. This effect was found to be reversible. Our results provide the first direct in vivo evidence for the contribution of gap junction communication in mechanisms of neural synchrony, underlying the production of theta in in vivo conditions. [ABSTRACT FROM AUTHOR]

Individual neurons in the medial septum and diagonal band fire in phase with, and appear to act as a ‘pacemaker’ of, the hippocampal theta rhythm. We investigated the relationships of periodic EEG both among various parts of the septum and with dorsal hippocampal theta recorded concurrently in freely moving rats. Most septal sites showed theta rhythm concurrent with hippocampal theta during locomotion. However, periods with theta at hippocampal but not septal sites were more frequent than the reverse. Theta waves in different parts of the septum were synchronized with each other but medial septal sites showed less frequent theta than other sites. The phase delays between medial and lateral septal sites were < 10 ms, suggesting that the hippocampus does not act as a simple relay between the two. Spectral analysis revealed periods (> 5 s) of theta at hippocampal sites co-occurring with rhythms at multiple septal sites that were slower than theta. Even slower were the ‘slow septal waves’ (mean 2.7 Hz), which were present in the absence of locomotion and did not ‘drive’ the hippocampus. Our data suggest that the pacemaker of hippocampal theta may best be thought of as a set of functionally differentiated components rather than as a single homogenous unit. [ABSTRACT FROM AUTHOR]

The hippocampal theta rhythm is generated by the pacemaker activity of the medial septum-diagonal band of Broca (MS/DBB) neurons. These nuclei are influenced by brainstem structures that modulate the theta rhythm. The aim of the present work is to determine whether the nucleus incertus (NI), which has important anatomical connections with the MS/DBB, contributes to the hippocampal theta rhythm generation in rats. Hippocampal field activity was recorded in urethane-anaesthetized rats. Electrical stimulation of the NI not only evoked theta rhythm in the hippocampus, but also decreased the amplitude of delta waves. Unit recordings in the NI revealed either a non-rhythm discharge pattern in most neurons (76%), or a rhythm activity at 13–25 Hz in the remaining neurons. The firing rate of these neurons increased during the presence of theta rhythm evoked by either sensory or reticularis pontis oralis nucleus (RPO) stimulation. Electrolytic lesions of NI, or the microinjection of the γ-aminobutyric acid (GABA)A agonist muscimol, abolished the theta rhythm evoked by RPO stimulation. Consequently, the NI may be a relay station between brainstem structures and the MS/DBB in the control of the hippocampal theta rhythm generation. [ABSTRACT FROM AUTHOR]

One hundred and seven cells were recorded extracellularly in hippocampal formation (HPC) slices during carbachol-induced theta. The data obtained provided evidence of a population of HPC neurons which, when activated cholinergically, participate in the generation of in vitro theta. The activity patterns of in vitro recorded theta-related cells were shown to be similar to those of theta-related cells recorded in vivo and cells recorded in vitro during cholinergically induced theta, and non-theta intervals were successfully classified according to previously developed criteria for in vivo recorded theta-related cells. The current in vitro experiments showed that, in addition to theta-on and theta-off cells, the HPC contained cells that were probably involved in programming the appearance and duration of theta epochs and the intervals between theta epochs. These novel types of cells were termed ’gating cells’. [ABSTRACT FROM AUTHOR]

The mesocortical dopamine (DA) input to the prefrontal cortex (PFC) is crucial for processing short-term working memory (STWM) to guide forthcoming behavior. Short-term plasticity-like post-tetanic potentiation (PTP, < 3 min) and short-term potentiation (STP, < 10 min) may underlie STWM. Using whole-cell voltage-clamp recordings, mixed glutamatergic excitatory postsynaptic currents (EPSCs) evoked by layer III or layer V stimulation (0.5 or 0.067 Hz) were recorded from layer V pyramidal neurons. With 0.5 Hz basal stimulation of layer III, brief tetani (2 × 50 Hz) induced a homosynaptic PTP (decayed: ∼1 min). The D1-like antagonist SCH23390 (1 µ m) increased the PTP amplitude and decay time without inducing changes to the tetanic response. The tetani may evoke endogenous DA release, which activates a presynaptic D1-like receptor to inhibit glutamate release to modulate PTP. With a slower (0.067 Hz) basal stimulation, the same tetani induced STP (lasting ∼4 min, but only at 2× intensity only) that was insignificantly suppressed by SCH23390. With stimulation of layer-V→V inputs at 0.5 Hz, layer V tetani yielded inconsisitent responses. However, at 0.067 Hz, tetani at double the intensity resulted in an STP (lasting ∼6 min), but a long-term depression after SCH23390 application. Endogenous DA released by tetanic stimulation can interact with a D1-like receptor to induce STP in layer V→V synapses that receive slower (0.067 Hz) frequency inputs, but suppresses PTP at layer III→V synapses that receive higher (0.5 Hz) frequency inputs. This D1-like modulation of layer- and frequency-specific synaptic responses in the PFC may contribute to STWM processing. [ABSTRACT FROM AUTHOR]

The medial septal diagonal band complex (MS/DB), made up of cholinergic and GABAergic neurons, plays an important role in the generation of the hippocampal theta rhythm. A GABAergic neuron type in the MS/DB that has fast spiking properties was shown previously to contain parvalbumin immunoreactivity and to form axosomatic connections with unidentified somata. The aim in the current study was to determine the neurochemical identities of these target neurons. In slices and in perfused-fixed brain, staining for parvalbumin immunoreactivity first of all revealed the presence of two types of parvalbumin-positive somata in the MS/DB: medially located neurons with parvalbumin-positive basket-like terminals on them, and more laterally located neurons with fewer parvalbumin-positive contacts on them. In MS/DB slices, the terminals of fast spiking neurons filled with biocytin correspondingly made either numerous contacts that surrounded the parvalbumin-positive cell body in basket-like formation, or 1–5 contacts on a localized patch of the soma. These contacts were shown by electron microscopy to form synaptic junctions. No terminals of biocytin-filled fast spiking neurons were observed on cholinergic neurons, and dual staining in perfused-fixed brain did not reveal the presence of parvalbumin-containing terminals on cholinergic somata. Our results suggest therefore that there are two subtypes of parvalbumin-containing neuron in the MS/DB, and that these are interconnected via axosomatic synapses. The contrasting topographical organization of the two types of parvalbumin-containing neuron suggests that they may receive different types of afferent input, but this will require substantiation in future studies. We propose that generation of rhythmic activity in the MS/DB is controlled by contrasting contributions from two types of parvalbumin-positive neuron, and that the role of the cholinergic neuron is modulatory. [ABSTRACT FROM AUTHOR]

Hippocampal learning and memory tasks are tightly coupled to the hippocampal theta rhythm, which is critically dependent on the medial septum/diagonal band of Broca (MSDB) although the underlying mechanisms remain unclear. The MSDB sends both cholinergic and GABAergic projections to the hippocampus. Here we show that: (i) septo-hippocampal GABAergic but not cholinergic neurons have a pacemaking current, the H-current, and that its selective blockade by ZD7288 reduces their spontaneous firing in rat brain slices; and (ii), local infusions of ZD7288 into the MSDB reduce exploration and sensory evoked hippocampal theta bursts in behaving rats. Thus, the H-current in septohippocampal GABAergic neurons modulates the hippocampal theta rhythm. [ABSTRACT FROM AUTHOR]