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Pre‐stimulus electroencephalogram (EEG) oscillations, especially in the alpha range (8–13 Hz), can affect the sensitivity to temporal lags between modalities in multisensory perception. The effects of alpha power are often explained in terms of alpha's inhibitory functions, whereas effects of alpha frequency have bolstered theories of discrete perceptual cycles, where the length of a cycle, or window of integration, is determined by alpha frequency. Such studies typically employ visual detection paradigms with near‐threshold or even illusory stimuli. It is unclear whether such results generalize to above‐threshold stimuli. Here, we recorded EEG, while measuring temporal discrimination sensitivity in a temporal‐order judgement task using above‐threshold auditory and visual stimuli. We tested whether the power and instantaneous frequency of pre‐stimulus oscillations predict audiovisual temporal discrimination sensitivity on a trial‐by‐trial basis. By applying a jackknife procedure to link single‐trial pre‐stimulus oscillatory power and instantaneous frequency to psychometric measures, we identified a posterior cluster where lower alpha power was associated with higher temporal sensitivity of audiovisual discrimination. No statistically significant relationship between instantaneous alpha frequency and temporal sensitivity was found. These results suggest that temporal sensitivity for above‐threshold multisensory stimuli fluctuates from moment to moment and is indexed by modulations in alpha power. [ABSTRACT FROM AUTHOR]

Pre‐stimulus oscillatory neural activity has been linked to the level of awareness of sensory stimuli. More specifically, the power of low‐frequency oscillations (primarily in the alpha‐band, i.e., 8–14 Hz) prior to stimulus onset is inversely related to measures of subjective performance in visual tasks, such as confidence and visual awareness. Intriguingly, the same EEG signature does not seem to influence objective measures of task performance (i.e., accuracy). We here examined whether this dissociation holds when stringent accuracy measures are used. Previous EEG‐studies have employed 2‐alternative forced choice (2‐AFC) discrimination tasks to link pre‐stimulus oscillatory activity to correct/incorrect responses as an index of accuracy/objective performance at the single‐trial level. However, 2‐AFC tasks do not provide a good estimate of single‐trial accuracy, as many of the responses classified as correct will be contaminated by guesses (with the chance correct response rate being 50%). Here instead, we employed a 19‐AFC letter identification task to measure accuracy and the subjectively reported level of perceptual awareness on each trial. As the correct guess rate is negligible (~5%), this task provides a purer measure of accuracy. Our results replicate the inverse relationship between pre‐stimulus alpha/beta‐band power and perceptual awareness ratings in the absence of a link to discrimination accuracy. Pre‐stimulus oscillatory phase did not predict either subjective awareness or accuracy. Our results hence confirm a dissociation of the pre‐stimulus EEG power–task performance link for subjective versus objective measures of performance, and further substantiate pre‐stimulus alpha power as a neural predictor of visual awareness. [ABSTRACT FROM AUTHOR]

Resistance to pharmacological treatment poses a notable challenge for psychiatry. Such cases are usually treated with brain stimulation techniques, including repetitive transcranial magnetic stimulation (rTMS) and electroconvulsive therapy (ECT). Empirical evidence links treatment resistance to insufficient brain plasticity and chronic inflammation. Therefore, this study encompasses analysis of neurotrophic and inflammatory factors in psychiatric patients undergoing rTMS and ECT in order to refine the selection of patients and predict clinical outcomes. This study enrolled 25 drug‐resistant depressive patients undergoing rTMS and 31 drug‐resistant schizophrenia patients undergoing ECT. Clinical efficacy of brain stimulation therapies was gauged using MADRS and HAM‐D scales in the depression group and PANSS scale in the schizophrenia group. Blood‐derived BDNF, VEGF, and TNFα were analysed during the treatment course. For reference, 19 healthy control subjects were also enrolled. After statistical analysis, no significant differences were detected in BDNF, VEGF, and TNFα concentrations among healthy, depressive, and schizophrenic subject groups before the treatment. However, depressive patient treatment with rTMS has increased BDNF concentration, while schizophrenic patient treatment with ECT has lowered the concentration of TNFα. Our findings suggest that a lower initial TNFα concentration could be a marker for treatment success in depressed patients undergoing rTMS, whereas in schizophrenic patient group treated with ECT, a higher concentration of VEGF correlates to milder symptoms post‐treatment, especially in the negative scale. [ABSTRACT FROM AUTHOR]

Genetic mediation of cortical plasticity and the role genetic variants play in previously observed response variability to transcranial direct current stimulation (tDCS) have become important issues in the tDCS literature in recent years. This study investigated whether inter‐individual variability to tDCS was in‐part genetically mediated. In 61 healthy males, anodal‐tDCS (a‐tDCS) and sham‐tDCS were administered to the primary motor cortex at 1 mA for 10‐min via 6 × 4 cm active and 7 × 5 cm return electrodes. Twenty‐five single‐pulse transcranial magnetic stimulation (TMS) motor evoked potentials (MEP) were recorded to represent corticospinal excitability (CSE). Twenty‐five paired‐pulse MEPs were recorded with 3 ms inter‐stimulus interval (ISI) to assess intracortical inhibition (ICI) via short‐interval intracranial inhibition (SICI) and 10 ms ISI for intracortical facilitation (ICF). Saliva samples were tested for specific genetic polymorphisms in genes encoding for excitatory and inhibitory neuroreceptors. Individuals were sub‐grouped based on a pre‐determined threshold and via statistical cluster analysis. Two distinct subgroups were identified, increases in CSE following a‐tDCS (i.e. Responders) and no increase or even reductions in CSE (i.e. Non‐responders). No changes in ICI or ICF were reported. No relationships were reported between genetic polymorphisms in excitatory receptor genes and a‐tDCS responders. An association was reported between a‐tDCS responders and GABRA3 gene polymorphisms encoding for GABA‐A receptors suggesting potential relationships between GABA‐A receptor variations and capacity to undergo tDCS‐induced cortical plasticity. In the largest tDCS study of its kind, this study presents an important step forward in determining the contribution genetic factors play in previously observed inter‐individual variability to tDCS. [ABSTRACT FROM AUTHOR]

Action preparation is associated with a transient decrease of corticospinal excitability just before target onset. We have previously shown that the prospect of reward modulates preparatory corticospinal excitability in a Simon task. While the conflict in the Simon task strongly implicates the motor system, it is unknown whether reward prospect modulates preparatory corticospinal excitability in tasks that implicate the motor system less directly. To that effect, we examined reward‐modulated preparatory corticospinal excitability in the Stroop task. We administered a rewarded cue‐target delay paradigm using Stroop stimuli that afforded a left or right index finger response. Single‐pulse transcranial magnetic stimulation was administered over the left primary motor cortex and electromyography was obtained from the right first dorsal interosseous muscle. In line with previous findings, there was a preparatory decrease in corticospinal excitability during the delay period. In contrast to our previous study using the Simon task, preparatory corticospinal excitability was not modulated by reward. Our results indicate that reward‐modulated changes in the motor system depend on specific task‐demands, possibly related to varying degrees of motor conflict. [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]

Human perception of perithreshold stimuli critically depends on oscillatory EEG activity prior to stimulus onset. However, it remains unclear exactly which aspects of perception are shaped by this pre‐stimulus activity and what role stochastic (trial‐by‐trial) variability plays in driving these relationships. We employed a novel jackknife approach to link single‐trial variability in oscillatory activity to psychometric measures from a task that requires judgement of the relative length of two line segments (the landmark task). The results provide evidence that pre‐stimulus alpha fluctuations influence perceptual bias. Importantly, a mediation analysis showed that this relationship is partially driven by long‐term (deterministic) alpha changes over time, highlighting the need to account for sources of trial‐by‐trial variability when interpreting EEG predictors of perception. These results provide fundamental insight into the nature of the effects of ongoing oscillatory activity on perception. The jackknife approach we implemented may serve to identify and investigate neural signatures of perceptual relevance in more detail. We employed a jackknife method to link pre‐stimulus neural oscillations to psychometric measures during line bisection performance. The analysis identified both spontaneous trial‐by‐trial (stochastic) and systematic long‐term (deterministic) predictors of visuospatial bias, but no predictors of visual sensitivity. The approach we implemented helps to further characterize the influence of ongoing neural activity on perception and cognition. [ABSTRACT FROM AUTHOR]

Short latency afferent inhibition ( SAI) is a paired-pulse transcranial magnetic stimulation ( TMS) protocol that consists in the inhibition of the motor evoked potentials ( MEPs) by afferent sensory impulses. SAI is thought to be mediated by cholinergic projections over M1 and can be considered a putative marker of central cholinergic activity. It is known that memory processes are regulated by acetylcholine. Nonetheless, the influence of memory tasks on SAI has not been investigated. Here we tested changes in SAI circuits in healthy subjects performing a computerized non-verbal recognition memory task ( RMT) requiring to recognize previously encoded faces. SAI protocol was recorded during five phases of the RMT: baseline, encoding, consolidation, retrieval, and post-task. In the control task, subjects were asked to judge a visual feature of not previously presented faces. SAI protocol was applied over the same conditions as in the RMT. We found that SAI remarkably increases during the retrieval phase of the RMT as compared to baseline. On the other hand no change was observed during the control task. These findings show that SAI can be modulated by ongoing memory processes and support the hypothesis that SAI can be considered as a neurophysiological marker of central cholinergic activity. [ABSTRACT FROM AUTHOR]

Spontaneous modulations of corticospinal excitability during action observation have been interpreted as evidence for the activation of internal motor representations equivalent to the observed action. Alternatively or complementary to this perspective, growing evidence shows that motor activity during observation of rhythmic movements can be modulated by direct visuomotor couplings and dynamical entrainment. In-phase and anti-phase entrainment spontaneously occur, characterized by cyclic movements proceeding simultaneously in the same (in-phase) or opposite (anti-phase) direction. Here we investigate corticospinal excitability during the observation of vertical oscillations of an index finger using Transcranial Magnetic Stimulation ( TMS). Motor-evoked potentials ( MEPs) were recorded from participants' flexor and extensor muscles of the right index finger, placed in either a maximal steady flexion or extension position, with stimulations delivered at maximal flexion, maximal extension or mid-trajectory of the observed finger oscillations. Consistent with the occurrence of dynamical motor entrainment, increased and decreased MEP responses - suggesting the facilitation of stable in-phase and anti-phase relations but not an unstable 90° phase relation - were found in participants' flexors. Anti-phase motor facilitation contrasts with the activation of internal motor representation as it involves activity in the motor system opposite from activity required for the execution of the observed movement. These findings demonstrate the relevance of dynamical entrainment theories and methods for understanding spontaneous motor activity in the brain during action observation and the mechanisms underpinning coordinated movements during social interaction. [ABSTRACT FROM AUTHOR]

Primary motor cortex (M1) excitability is modulated following a single session of cycling exercise. Specifically, short-interval intracortical inhibition and intracortical facilitation are altered following a session of cycling, suggesting that exercise affects the excitability of varied cortical circuits. Yet we do not know whether a session of exercise also impacts the excitability of interhemispheric circuits between, and other intracortical circuits within, M1. Here we present two experiments designed to address this gap in knowledge. In experiment 1, single and paired pulse transcranial magnetic stimulation ( TMS) were used to measure intracortical circuits including, short-interval intracortical facilitation ( SICF) tested at 1.1, 1.5, 2.7, 3.1 and 4.5 ms interstimulus intervals ( ISIs), contralateral silent period ( CSP) and interhemispheric interactions by measuring transcallosal inhibition ( TCI) recorded from the abductor pollicus brevis muscles. All circuits were assessed bilaterally pre and two time points post (immediately, 30 min) moderate intensity lower limb cycling. SICF was enhanced in the left hemisphere after exercise at the 1.5 ms ISI. Also, CSP was shortened and TCI decreased bilaterally after exercise. In Experiment 2, corticospinal and spinal excitability were tested before and after exercise to investigate the locus of the effects found in Experiment 1. Exercise did not impact motor-evoked potential recruitment curves, Hoffman reflex or V-wave amplitudes. These results suggest that a session of exercise decreases intracortical and interhemispheric inhibition and increases facilitation in multiple circuits within M1, without concurrently altering spinal excitability. These findings have implications for developing exercise strategies designed to potentiate M1 plasticity and skill learning in healthy and clinical populations. [ABSTRACT FROM AUTHOR]

To explore the link between Sense of Embodiment (SoE) over a virtual hand and physiological regulation of skin temperature, 24 healthy participants were immersed in virtual reality through a Head Mounted Display and had their real limb temperature recorded by means of a high-sensitivity infrared camera. Participants observed a virtual right upper limb (appearing either normally, or with the hand detached from the forearm) or limb-shaped non-corporeal control objects (continuous or discontinuous wooden blocks) from a first-person perspective. Subjective ratings of SoE were collected in each observation condition, as well as temperatures of the right and left hand, wrist and forearm. The observation of these complex, body and body-related virtual scenes resulted in increased real hand temperature when compared to a baseline condition in which a 3d virtual ball was presented. Crucially, observation of non-natural appearances of the virtual limb (discontinuous limb) and limb-shaped non-corporeal objects elicited high increase in real hand temperature and low SoE. In contrast, observation of the full virtual limb caused high SoE and low temperature changes in the real hand with respect to the other conditions. Interestingly, the temperature difference across the different conditions occurred according to a topographic rule that included both hands. Our study sheds new light on the role of an external hand's visual appearance and suggests a tight link between higher-order bodily self-representations and topographic regulation of skin temperature. [ABSTRACT FROM AUTHOR]

We tend to express more positive judgments and behaviors toward individuals belonging to our own group compared to other (out-) groups. In this study, we assessed the role of the cerebellum and of the dorsomedial prefrontal cortex (dm PFC) - two regions critically implicated in social cognition processes - in mediating implicit valenced attitudes toward in-group and out-group individuals. To this aim, we used transcranial magnetic stimulation ( TMS) in combination with a standard attitude priming task, in which Caucasian participants had to categorize the valence of a series of adjectives primed by either an in-group or an out-group face. In two behavioral experiments, we found an in-group bias (i.e. faster categorization of positive adjectives when preceded by in-group faces) but no evidence of an out-group bias. Interestingly, TMS over both the dm PFC and over the (right) cerebellum significantly interfered with the modulation exerted by group membership on adjective valence classification, abolishing the in-group bias observed at baseline. Overall, our data suggest that both the dm PFC and the cerebellum play a causal role in mediating implicit social attitudes. [ABSTRACT FROM AUTHOR]

Responses to non-invasive brain stimulation are highly variable between subjects. Resting state functional connectivity was investigated as a marker of plasticity induced by anodal transcranial direct current stimulation ( tDCS). Twenty-six healthy adults (15 male, 26.4 ± 6.5 years) were tested. Experiment 1 investigated whether functional connectivity could predict modulation of corticospinal excitability following anodal tDCS. Experiment 2 determined test -retest reliability of connectivity measures. Three minutes of electroencephalography was recorded and connectivity was quantified with the debiased weighted phase lag index. Anodal (1 mA, 20 min) or sham tDCS was applied to the left primary motor cortex (M1), with a change in motor evoked potential amplitude recorded from the right first dorsal interosseous used as a marker of tDCS response. Connectivity in the high beta frequency (20-30 Hz) between an electrode approximating the left M1 (C3) and electrodes overlying the left parietal cortex was a strong predictor of tDCS response (cross-validated R2 = 0.69). Similar relationships were observed for alpha (8-13 Hz; R2 = 0.64), theta (4-7 Hz; R2 = 0.53), and low beta (14-19 Hz; R2 = 0.58) frequencies, however, test -retest reliability of connectivity measures was strongest for the high beta frequency model ( ICC = 0.65; good reliability). Further investigation of the high beta model found that greater connectivity between C3 and a cluster of electrodes approximately overlying the left parietal cortex was associated with stronger responses to anodal (rho = 0.61, P = 0.03), but not sham tDCS (rho = 0.43, P = 0.14). Functional connectivity is a strong predictor of the neuroplastic response to tDCS and may be one important characteristic to assist targeted tDCS application. [ABSTRACT FROM AUTHOR]

Paired-pulse transcranial magnetic stimulation ( TMS) can be used to probe inhibitory activity in primary motor cortex (M1). Recruitment of descending volleys with TMS depends on the induced current direction in M1. Anterior-posterior ( AP) stimulation preferentially activates late indirect- (I-) waves that are most susceptible to paired-pulse TMS. Threshold tracking TMS can assess intracortical inhibition; however, previous studies have only used a current direction that preferentially recruits early I-waves [posterior-anterior ( PA)]. Our objective was to examine intracortical inhibition with threshold tracking TMS designed to preferentially recruit early vs. late I-waves with PA and AP stimulation respectively. Electromyographic recordings were obtained from the right first dorsal interosseous muscle of 15 participants (21-50 years). Motor evoked potentials elicited by TMS over left M1 were recorded for PA, AP and lateromedial ( LM) induced currents, with I-wave recruitment calculated as the onset latency difference between PA- LM and AP- LM. Short- and long-interval intracortical inhibition ( SICI and LICI) were examined across a range of conditioning stimulus intensities and interstimulus intervals (3 and 100-260 ms) with threshold tracking TMS for PA and AP stimulation. SICI and LICI were greater for AP compared with PA current direction using threshold tracking. In addition, the efficacy of late I-wave recruitment was associated with the extent of SICI for AP but not PA stimulation, and was not associated with LICI. These findings indicate that threshold tracking with an AP-induced current provides a more robust and sensitive measure of M1 intracortical inhibition than PA. [ABSTRACT FROM AUTHOR]

Since the initial demonstration of linear effects of stimulation duration and intensity on the strength of after-effects associated with transcranial direct current stimulation ( tDCS), few studies have systematically assessed how varying these parameters modulates corticospinal excitability. Therefore, the objective of this study was to systematically evaluate the effects of anodal tDCS on corticospinal excitability at two stimulation intensities (1 mA, 2 mA) and durations (10 min, 20 min), and determine the value of several variables in predicting response. Two groups of 20 individuals received, in two separate sessions, 1 and 2 mA anodal tDCS (left primary motor cortex (M1)-right supra-orbital montage) for either 10- or 20-min. Transcranial magnetic stimulation was delivered over left M1 and motor evoked potentials ( MEPs) of the contralateral hand were recorded prior to tDCS and every 5 min for 20-min post- tDCS. The following predictive variables were evaluated: I-wave recruitment, stimulation intensity, baseline M1 excitability and inter-trial MEP variability. Results show that anodal tDCS failed to significantly modulate corticospinal excitability in all conditions. Furthermore, low response rates were identified across all parameter combinations. No baseline measure was significantly correlated with increases in MEP amplitude. However, a decrease in inter-trial MEP variability was linked to response to anodal tDCS. In conclusion, the present findings are consistent with recent reports showing high levels of inter-subject variability in the neurophysiological response to tDCS, which may partly explain inconsistent group results. Furthermore, the level of variability in the neurophysiological outcome measure, i.e. MEPs, appears to be related to response. [ABSTRACT FROM AUTHOR]

The ability to associate neutral stimuli with motivationally relevant outcomes is an important survival strategy. In this study, we used event-related potentials ( ERPs) to investigate brain dynamics of associative emotional learning when participants were confronted with multiple heterogeneous information. Participants viewed 144 different objects in the context of 144 different emotional and neutral background scenes. During each trial, neutral objects were shown in isolation and then paired with the background scene. All pairings were presented twice to compare ERPs in response to neutral objects before and after single association. After single pairing, neutral objects previously encoded in the context of emotional scenes evoked a larger P100 over occipital electrodes compared to objects that were previously paired with neutral scenes. Likewise, larger late positive potentials (LPPs) were observed over parieto-occipital electrodes (450-750 ms) for objects previously associated with emotional relative to neutral contexts. The LPP - but not P100 - enhancement was also related to subjective object/context binding. Taken together, our ERP data provide evidence for fast emotional associative learning, as reflected by heightened perceptual and sustained elaborative processing for neutral information previously encountered in emotional contexts. These findings could assist in understanding binding mechanisms in stress and anxiety, as well as in addiction and eating-related disorders. [ABSTRACT FROM AUTHOR]

Commission of errors and conflict between choices might induce behavioral modulations through adjustments in the executive control of behavior and altered patterns of these modulations are detected in neuropsychiatric disorders. We examined the effects of transcranial Direct Current Stimulation ( tDCS) applied over the dorsolateral prefrontal cortex ( DLPFC) on error- and conflict-induced behavioral modulations. Two separate cohorts of participants performed two clinically relevant tests of executive control, respectively. In the Wisconsin Card Sorting Test ( WCST), the relevant rule for matching items frequently changed and therefore participants had to detect these unannounced changes by trial and error and alter their rule-based behavior. In the Stop task, participants had to rapidly respond to a directional go-signal but inhibit their responses when a stop signal appeared after the go-signal. Each participant received tDCS (sham, cathodal or anodal) in three separate sessions. Errors led to a slower response in the next trial (post-error slowing) in both tasks. The tDCS significantly modulated the post-error slowing in both tasks but did not affect the behavioral adjustments induced by the conflict. The modulation of post-error slowing by tDCS were polarity-dependent and also trial specific appearing immediately after errors. In the WCST and Stop task, the post-error slowing may reflect different processes involved in shifting the behavior-guiding rule and adjustments in inhibitory control of responses, respectively, and we found that the effective tDCS polarity differed between the two tasks. Here, we show that in two separate cognitive tasks direct current stimulation of DLPFC significantly modulated error-induced behavioral modulations. [ABSTRACT FROM AUTHOR]

The ability to integrate auditory and visual information is critical for effective perception and interaction with the environment, and is thought to be abnormal in some clinical populations. Several studies have investigated the time window over which audiovisual events are integrated, also called the temporal binding window, and revealed asymmetries depending on the order of audiovisual input (i.e. the leading sense). When judging audiovisual simultaneity, the binding window appears narrower and non-malleable for auditory-leading stimulus pairs and wider and trainable for visual-leading pairs. Here we specifically examined the level of independence of binding mechanisms when auditory-before-visual vs. visual-before-auditory input is bound. Three groups of healthy participants practiced audiovisual simultaneity detection with feedback, selectively training on auditory-leading stimulus pairs (group 1), visual-leading stimulus pairs (group 2) or both (group 3). Subsequently, we tested for learning transfer (crossover) from trained stimulus pairs to non-trained pairs with opposite audiovisual input. Our data confirmed the known asymmetry in size and trainability for auditory-visual vs. visual-auditory binding windows. More importantly, practicing one type of audiovisual integration (e.g. auditory-visual) did not affect the other type (e.g. visual-auditory), even if trainable by within-condition practice. Together, these results provide crucial evidence that audiovisual temporal binding for auditory-leading vs. visual-leading stimulus pairs are independent, possibly tapping into different circuits for audiovisual integration due to engagement of different multisensory sampling mechanisms depending on leading sense. Our results have implications for informing the study of multisensory interactions in healthy participants and clinical populations with dysfunctional multisensory integration. [ABSTRACT FROM AUTHOR]

We aimed to assess the effects of concurrent cathodal transcranial direct current stimulation (c- tDCS) of two targets in a hemisphere, termed unihemispheric concurrent dual-site cathodal tDCS (c- tDCSUHCDS), on the size of M1 corticospinal excitability and its lasting effect. Secondary aims were to identify the mechanisms behind the efficacy of c- tDCSUHCDS and to evaluate the side effects of this new technique. Twelve healthy volunteers received 20 min c- tDCS under five conditions in a random order: M1 c- tDCS, c- tDCSUHCDS of M1-dorsolateral prefrontal cortex ( DLPFC), M1-primary sensory cortex (S1), M1-primary visual cortex (V1) and sham. The M1 corticospinal excitability of the first dorsal interossei muscle was assessed before, immediately after, and 30 min, 60 min and 24 h after the interventions. Short-interval intracortical inhibition ( SICI) and intracortical facilitation ( ICF) were also assessed, using a paired-pulse paradigm. Compared to conventional M1 c- tDCS, corticospinal excitability significantly increased following c- tDCSUHCDS of M1- DLPFC and M1-V1 for up to 24 h ( P = 0.001). Significant increases in ICF were observed following c- tDCSUHCDS of M1- DLPFC ( P = 0.005) and M1-V1 ( P = 0.002). Compared to baseline values, ICF and SICI increased significantly at T60 ( P < 0.001) and T24 h ( P < 0.001) following the concurrent c- tDCS of M1 and V1. Sham c- tDCSUHCDS did not induce any significant alteration. The corticospinal excitability increase was mainly accompanied by ICF increase, which indirectly indicates the activity of glutamergic mechanisms. The findings may help us to more fully understand the brain function and develop future motor learning studies. No significant excitability change induced by sham c- tDCSUHCDS suggests that there is no placebo effect associated with this new tDCS technique. [ABSTRACT FROM AUTHOR]

Motor surround inhibition is the neural mechanism that selectively favours the contraction of target muscles and inhibits nearby muscles to prevent unwanted movements. This inhibition was previously reported at the onset of a movement, but not during a tonic contraction. Cerebellar brain inhibition ( CBI) is reduced in active muscles during tonic activation; however, it has not been studied in the surround muscles. CBI was evaluated in the first dorsal interosseus ( FDI) muscle as the target muscle, and the abductor digiti minimi, flexor carpi radialis and extensor carpi radialis muscles as surround muscles, during rest and tonic activation of the FDI muscle in 21 subjects. Cerebellar stimulation was performed under magnetic resonance imaging-guided neuronavigation targeting lobule VIII of the cerebellar hemisphere. Stimulus intensities for cerebellar stimulation were based on the resting motor cortex threshold ( RMT) and adjusted for the depth difference between the cerebellar and motor cortices. We used 90-120% of the adjusted RMT as the conditioning stimulus intensity during rest. The intensity that generated the best CBI at rest in the FDI muscle was selected for use during tonic activation. During selective tonic activation of the FDI muscle, CBI was significantly reduced only for the FDI muscle, and not for the surround muscles. Unconditioned motor evoked potential sizes were increased in all muscles during FDI muscle tonic activation as compared with rest, despite background electromyography activity increasing only for the FDI muscle. Our study suggests that the cerebellum may play an important role in selective tonic finger movement by reducing its inhibition in the motor cortex only for the relevant agonist muscle. [ABSTRACT FROM AUTHOR]

Motor imagery (MI) training and anodal transcranial direct current stimulation (tDCS) applied over the primary motor cortex can independently improve hand motor function. The main objective of this double-blind, sham-controlled study was to examine whether anodal tDCS over the primary motor cortex could enhance the effects of MI training on the learning of a finger tapping sequence. Thirty-six right-handed young human adults were assigned to one of three groups: (i) who performed MI training combined with anodal tDCS applied over the primary motor cortex; (ii) who performed MI training combined with sham tDCS; and (iii) who received tDCS while reading a book. The MI training consisted of mentally rehearsing an eight-item complex finger sequence for 13 min. Before (Pre-test), immediately after (Post-test 1), and at 90 min after (Post-test 2) MI training, the participants physically repeated the sequence as fast and as accurately as possible. An ANOVA showed that the number of sequences correctly performed significantly increased between Pre-test and Post-test 1 and remained stable at Post-test 2 in the three groups (P < 0.001). Furthermore, the percentage increase in performance between Pre-test and Post-test 1 and Post-test 2 was significantly greater in the group that performed MI training combined with anodal tDCS compared with the other two groups (P < 0.05). As a potential physiological explanation, the synaptic strength within the primary motor cortex could have been reinforced by the association of MI training and tDCS compared with MI training alone and tDCS alone. [ABSTRACT FROM AUTHOR]

Cognitive functions such as numerical processing and spatial attention show varying degrees of lateralization. Transcranial direct current stimulation (tDCS) can be used to investigate how modulating cortical excitability affects performance of these tasks. This study investigated the effect of bi-parietal tDCS on numerical processing, spatial and sustained attention. It was hypothesized that tDCS would have distinct effects on these tasks because of varying lateralization (numerical processing left, spatial attention right) and that these effects are partly mediated by modulation of sustained attention. A single-blinded, crossover, sham-controlled study was performed. Eighteen healthy right-handed participants performed cognitive tasks during three sessions of oppositional parietal tDCS stimulation: sham; right anodal with left cathodal (RA/LC); and right cathodal with left anodal (RC/LA). Participants performed a number comparison task, a modified Posner task, a choice reaction task (CRT) and the rapid visual processing task (RVP). RA/LC tDCS impaired number comparison performance compared with sham, with slower responses to numerically close numbers pairs. RA/LC and RC/LA tDCS had distinct effects on CRT performance, specifically affecting vigilance level during the final block of the task. No effect of stimulation on the Posner task or RVP was found. It was demonstrated that oppositional parietal tDCS affected both numerical performance and vigilance level in a polarity-dependent manner. The effect of tDCS on numerical processing may partly be due to attentional effects. The behavioural effects of tDCS were specifically observed under high task demands, demonstrating the consequences of an interaction between stimulation type and cognitive load. [ABSTRACT FROM AUTHOR]

Although neuroimaging studies have consistently identified the temporoparietal junction ( TPJ) as a key brain region involved in social cognition, the literature is far from consistent with respect to lateralization of function. For example, during theory-of-mind tasks bilateral TPJ activation is found in some studies but only right hemisphere activation in others. Visual perspective-taking and imitation inhibition, which have been argued to recruit the same socio-cognitive processes as theory of mind, are associated with unilateral activation of either left TPJ (perspective taking) or right TPJ (imitation inhibition). The present study investigated the functional lateralization of TPJ involvement in the above three socio-cognitive abilities using transcranial direct current stimulation. Three groups of healthy adults received anodal stimulation over right TPJ, left TPJ or the occipital cortex prior to performing three tasks (imitation inhibition, visual perspective-taking and theory of mind). In contrast to the extant neuroimaging literature, our results suggest bilateral TPJ involvement in imitation inhibition and visual perspective-taking, while no effect of anodal stimulation was observed on theory of mind. The discrepancy between these findings and those obtained using neuroimaging highlight the efficacy of neurostimulation as a complementary methodological tool in cognitive neuroscience. [ABSTRACT FROM AUTHOR]

The primary aim of this study was to assess the effects of cathodal transcranial direct current stimulation (c- tDCS) over cortical regions of the pain neuromatrix, including the primary motor (M1), sensory (S1) and dorsolateral prefrontal ( DLPFC) cortices on M1/S1 excitability, sensory ( STh), and pain thresholds ( PTh) in healthy adults. The secondary aim was to evaluate the placebo effects of c- tDCS on induced cortical and behavioural changes. Before, immediately after and 30 min after c- tDCS the amplitude of N20-P25 components of somatosensory evoked potentials ( SEPs) and peak-to-peak amplitudes of motor evoked potentials ( MEPs) were measured under four different experimental conditions. STh and PTh for peripheral electrical and mechanical stimulation were also evaluated. c- tDCS of 0.3 mA was applied for 20 min. A blinded assessor evaluated all outcome measures. c- tDCS of M1, S1 and DLPFC significantly decreased the corticospinal excitability of M1 ( P < 0.05) for at least 30 min. Following the application of c- tDCS over S1, M1 and DLPFC, the amplitude of the N20-P25 component of SEPs decreased for at least 30 min ( P < 0.05). Compared with baseline values, significant STh and PTh increases were observed after c- tDCS of these three sites. Decreasing the level of S1 and M1 excitability, following S1, M1 and DLPFC stimulation, confirmed the functional connectivities between these cortical sites involved in pain processing. Furthermore, increasing the level of STh/ PTh after c- tDCS of these sites indicated that stimulation of not only M1 but also S1 and DLPFC could be considered a technique to decrease the level of pain in patients. [ABSTRACT FROM AUTHOR]

An increasing amount of studies apply repetetive transcranial magnetic stimulation (rTMS) to treat chronic tinnitus, yet the neurophysiological impacts have remained largely obscure. Several studies show that endogenous brain rhythms may be enhanced via diverse brain stimulation techniques applying rhythmic stimulation. Here, we investigated in normal hearing participants whether application of rTMS (left auditory cortex) with an individualized alpha frequency was capable of increasing alpha activity in stimulated auditory regions in a sustained manner. Behavioral intensity discrimination performance worsened for the rTMS group as compared to Sham. Electroencephalography (EEG) data, however, clearly show that this functional inhibition is not accompanied by increases of auditory cortical alpha. Even though more pronounced power reductions for the rTMS group were observed at slower frequencies (delta to theta range) at stimulated and other sites of the left hemisphere, they were unrelated to behavioral changes. Our results also strongly suggest that the amount of power modulations at these slower frequencies is strongly dependent on pre-rTMS power, thus supporting current state-dependency notions. Strong relationships to behavioral changes were in particular observed for anterior cingulate cortex (ACC) beta power and posterior cingulate cortex (PCC) beta connectivity. Moreover, these beta band measures were strongly inter-related and when viewed together specifically sensitive to behavioral changes in the rTMS group. We conclude that currently alpha frequency rTMS is not a promising avenue for the treatment of chronic tinnitus and that beneficial effects could be mediated via nonauditory systems. Our study argues for the value of combined EEG-TMS studies when investigating the impacts of rTMS. Hum Brain Mapp 35:14-29, 2014. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Although oscillatory activity in the alpha band was traditionally associated with lack of alertness, more recent work has linked it to specific cognitive functions, including visual attention. The emerging method of rhythmic transcranial magnetic stimulation (TMS) allows causal interventional tests for the online impact on performance of TMS administered in short bursts at a particular frequency. TMS bursts at 10 Hz have recently been shown to have an impact on spatial visual attention, but any role in featural attention remains unclear. Here we used rhythmic TMS at 10 Hz to assess the impact on attending to global or local components of a hierarchical Navon-like stimulus (D. Navon (1977) Forest before trees: The precedence of global features in visual perception. Cognit. Psychol., 9, 353), in a paradigm recently used with TMS at other frequencies (V. Romei, J. Driver, P.G. Schyns & G. Thut. (2011) Rhythmic TMS over parietal cortex links distinct brain frequencies to global versus local visual processing. Curr. Biol., 2, 334-337). In separate groups, left or right posterior parietal sites were stimulated at 10 Hz just before presentation of the hierarchical stimulus. Participants had to identify either the local or global component in separate blocks. Right parietal 10 Hz stimulation (vs. sham) significantly impaired global processing without affecting local processing, while left parietal 10 Hz stimulation vs. sham impaired local processing with a minor trend to enhance global processing. These 10 Hz outcomes differed significantly from stimulation at other frequencies (i.e. 5 or 20 Hz) over the same site in other recent work with the same paradigm. These dissociations confirm differential roles of the two hemispheres in local vs. global processing, and reveal a frequency-specific role for stimulation in the alpha band for regulating feature-based visual attention. [ABSTRACT FROM AUTHOR]

The effects of repetitive transcranial magnetic stimulation (rTMS) on cortical excitability are usually inferred from indirect indexes, such as EMG responses. It has now become possible to directly evaluate rTMS impact by means of concurrent EEG recording. The aim of this study was to examine the modulation induced by high frequency rTMS (20 Hz) over left primary motor cortex on the ongoing oscillatory activity. Thirteen subjects underwent two sham and a real rTMS session while acquiring EEG. Event-related desynchronization/synchronization was calculated for the α and β bands. rTMS induced a dose-dependent increase in synchronization in both bands over central and parietal sites. The strongest effect found for the α band outlasted the end of the stimulation. Considering previous studies, our data suggest that α generation may represent an intrinsic induced response and a basic response signature to TMS targeting the human resting motor cortex. [ABSTRACT FROM AUTHOR]

Invasive recordings of local field potentials (LFPs) have been used to 'read the mind' of monkeys in real time. Here we investigated whether noninvasive field potentials estimated from the scalp-recorded electroencephalogram (EEG) using the ELECTRA source localization algorithm could provide real-time decoding of mental states in healthy humans. By means of pattern recognition techniques on 500-ms EEG epochs, we were able to discriminate accurately from single trials which of four categories of visual stimuli the subjects were viewing. Our results show that it is possible to reproduce the decoding accuracy previously obtained in animals with invasive recordings. A comparison between the decoding results and the subjects' behavioral performance indicates that oscillatory activity (OA), elicited in specific brain regions) codes better for the visual stimulus category presented than the subjects' actual response, i.e., is insensitive to voluntary or involuntary errors. The identification of brain regions participating in the decoding process allowed us to construct 3D-functional images of the task-related OA. These images revealed the activation of brain regions known for their involvement in the processing of this type of visual stimuli. Electrical neuroimaging therefore appears to have the potential to establish what the brain is processing while the stimuli are being seen or categorized, i.e., concurrently with sensory-perceptual processes. Hum Brain Mapp 2006. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Electroencephalographic studies in humans have demonstrated that orienting of visual attention induces a decrease in oscillatory α-band activity (α-desynchronization) over cortical areas tuned to the attended visual space. This is interpreted as reflecting intentionally enhanced excitability of these areas to facilitate upcoming visual processing. However, the inverse mechanism might also apply. Brain areas that process task-irrelevant space might be actively suppressed by increased α-activity (α-synchronization) to protect against input of distracter information. In the present study, we demonstrate that such suppression mechanisms are highly selective and are taking place even without distracters that need to be ignored. During voluntary orienting of attention, we found α-synchronization to dominate over desynchronization, to be topographically specific for each of eight attention positions, and to occur over areas processing unattended space in a retinotopically organized pattern. This indicates that α-synchronization is an important component of selective attention, serving active suppression of unattended positions during visual spatial orienting. [ABSTRACT FROM AUTHOR]

Response to a stimulus is faster when a subject is attending and knows beforehand how to respond. It has been suggested recently that this occurs because ongoing neuronal activity is spatially and temporally structured during states of expectancy preceding a stimulus. This mechanism is believed to mediate top-down processing, facilitating the early grouping and selection of distributed neuronal ensembles implicated in ensuing sensory-motor processing. To validate this model, it must be shown that some features of this early ongoing neural activity are correlated with subsequent perceptual decisions or behavioral events. We investigated this hypothesis in an electrophysiologic study in 12 subjects carrying out a simple visuomotor reaction-time task. Local field potentials (LFP) at each brain voxel were estimated using a linear distributed inverse solution termed 'ELECTRA' for each single trial of each subject. The energy of oscillations for different frequency bands was computed for the period between the warning cue and visual stimuli by applying a time-frequency decomposition to the estimated LFP. A nonparametric correlation coefficient was then calculated between energy of oscillations and reaction times for each single sweep. Gamma band oscillatory activity in a frontoparietal network before stimulus onset significantly correlated with reaction time for a significant amount of subjects. These results provide direct evidence for the role of neural oscillations as a top-down attentional control mechanism that mediates the speed of motor actions. Hum. Brain Mapping 24:50-58, 2005. © 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Electroencephalographic studies in humans have demonstrated that orienting of visual attention induces a decrease in oscillatory alpha-band activity (alpha-desynchronization) over cortical areas tuned to the attended visual space. This is interpreted as reflecting intentionally enhanced excitability of these areas to facilitate upcoming visual processing. However, the inverse mechanism might also apply. Brain areas that process task-irrelevant space might be actively suppressed by increased alpha-activity (alpha-synchronization) to protect against input of distracter information. In the present study, we demonstrate that such suppression mechanisms are highly selective and are taking place even without distracters that need to be ignored. During voluntary orienting of attention, we found alpha-synchronization to dominate over desynchronization, to be topographically specific for each of eight attention positions, and to occur over areas processing unattended space in a retinotopically organized pattern. This indicates that alpha-synchronization is an important component of selective attention, serving active suppression of unattended positions during visual spatial orienting.