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Highlights • Focal electrical stimulation of the DNLL (ES DNLL) produces variation in response parameters of modulated IC neurons. • Brief ES DNLL produces variation in the number of impulses, response latency and duration of modulated IC neurons. • 30-minute short-term ES DNLL also produces BF and MT shift. • Response variation after 30-minute ES DNLL recovers in different manner and time course among modulated IC neurons. Abstract In the ascending auditory pathway, the central nucleus of the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from many bilateral lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and from the auditory cortex. All these presynaptic excitatory and inhibitory inputs dynamically shape and modulate the auditory response properties of individual IC neurons. For this reason, acoustic response properties vary among individual IC neurons due to different activity pattern of presynaptic inputs. The present study examines modulation of auditory response properties of IC neurons by combining sound stimulation with focal electrical stimulation of the contralateral dorsal nucleus of the lateral lemniscus (referred to as ES DNLL) in the albino mouse. Brief ES DNLL produces variation (increase or decrease) in the number of impulses, response latency and discharge duration of modulated IC neurons. Additionally, 30-minute short-term ES DNLL alone produces variation in the best frequency (BF) and minimum threshold (MT) of modulated IC neurons. These varied response parameters recover in different manner and time course among individual modulated IC neurons. Possible pathways and neural mechanisms underlying these findings are discussed. [ABSTRACT FROM AUTHOR]

The Mongolian gerbil (Meriones unguiculatus) is widely used as a model organism for the human auditory system. Its hearing range is very similar to ours and it uses the same mechanisms for sound localization. The auditory circuits underlying these functions have been characterized. However, important mechanistic details are still under debate. To elucidate these issues, precise and reversible optogenetic manipulation of neuronal activity in this complex circuitry is required. However, genetic and genomic resources for the Mongolian gerbil are poorly developed. Here, we demonstrate a reliable gene delivery system using an AAV8(Y337F)-pseudotyped recombinant adeno-associated virus (AAV) 2-based vector in which the pan-neural human synapsin (hSyn) promoter drives neuron-specific expression of CatCH (Ca2+-permeable channelrhodopsin) or NpHR3.0 (Natronomonas pharaonis halorhodopsin). After stereotactic injection into the gerbil's auditory brainstem (medial nucleus of the trapezoid body, dorsal nucleus of the lateral lemniscus) and midbrain [inferior colliculus (IC)], we characterized CatCH- and/or NpHR3.0-transduced neurons in acute brain slices by means of whole-cell patchclamp recordings. As the response properties of optogenetic tools strongly depend on neuronal biophysics, this parameterization is crucial for their in vivo application. In a proof-of-principle experiment in anesthetized gerbils, we observed strong suppression of sound-evoked neural responses in the dorsal nucleus of the lateral lemniscus (DNLL) and IC upon light activation of NpHR3.0. The successful validation of gene delivery and optogenetic tools in the Mongolian gerbil paves the way for future studies of the auditory circuits in this model system. [ABSTRACT FROM AUTHOR]

Objective: We tested the hypothesis that somatosensory system injury would more strongly affect movement than motor system injury in children with unilateral cerebral palsy (USCP). This hypothesis was based on how somatosensory and corticospinal circuits adapt to injury during development; whereas the motor system can maintain connections to the impaired hand from the uninjured hemisphere, this does not occur in the somatosensory system. As a corollary, cortical injury strongly impairs sensory function, so we hypothesized that cortical lesions would impair hand function more than subcortical lesions.Methods: Twenty-four children with unilateral cerebral palsy had physiological and anatomical measures of the motor and somatosensory systems and lesion classification. Motor physiology was performed with transcranial magnetic stimulation and somatosensory physiology with vibration-evoked electroencephalographic potentials. Tractography of the corticospinal tract and the medial lemniscus was performed with diffusion tensor imaging, and lesions were classified by magnetic resonance imaging. Anatomical and physiological results were correlated with measures of hand function using 2 independent statistical methods.Results: Children with disruptions in the somatosensory connectivity and cortical lesions had the most severe upper extremity impairments, particularly somatosensory function. Motor system connectivity was significantly correlated with bimanual function, but not unimanual function or somatosensory function.Interpretation: Both sensory and motor connectivity impact hand function in children with USCP. Somatosensory connectivity could be an important target for recovery of hand function in children with USCP. Ann Neurol 2017;82:766-780. [ABSTRACT FROM AUTHOR]

We used magnetic resonance imaging to study the anatomy of cortical regions, nuclear groups, and major tracts in the brain of a monotreme, i.e., the short-beaked echidna (Tachyglossus aculeatus). Our specimens were from a collection held at the Australian Museum in Sydney and had been stored in formaldehyde solution for at least 70 years. Despite this, we were able to detect fine detail in the nuclear divisions of structures as well as in fiber tracts. In particular, we could detect the medial lemniscus as it approached the ventral posterior thalamic nucleus, subdivisions within the ventral posterior thalamic nucleus, lamination and subdivisions within the hippocampal formation, components of the olfactory pathways, and nuclei within the temporal amygdala. We were able to map the topography of subcortical white matter and relate it to cortical regions determined on the basis of physiology, as well as chemical and cytoarchitecture. As expected, dense aggregations of fibers were noted in association with the primary sensory areas of the isocortex (somatosensory, visual, and auditory) and connecting primary olfactory regions (intrabulbar anterior commissure and associated fibers). We found longitudinal fibers in the basal forebrain (medial forebrain bundle) and brainstem (corticopontine and corticospinal tracts), as well as a dense array of fibers associated with the vermal and paravermal zones of the anterior lobe of the cerebellum. We also observed previously unrecognized fiber systems, i.e., commissural connections between the paired frontal isocortical fields (dorsal Fr1), dense fibers to the retrosplenial association cortex, and prominent, paired longitudinal fiber bundles in the dorsal forebrain (longitudinal fasciculus) that intersected the dorsal anterior commissure. The connectome results are consistent with the known neuroanatomy of this monotreme and they extend our knowledge of the fiber topography within this unusual brain. Our findings demonstrate the feasibility of using this sort of imaging of archived brains to analyze the neuroanatomy of rare, endangered, and evolutionarily significant species. [ABSTRACT FROM AUTHOR]

A major hallmark of cortical organization is the existence of a variable number of layers, i.e., sheets of neurons stacked on top of each other, in which neurons have certain commonalities. However, even for the neocortex, variable numbers of layers have been described and it is just a convention to distinguish six layers from each other. Whether cortical layers are a structural epiphenomenon caused by developmental dynamics or represent a functionally important modularization of cortical computation is still unknown. Here we present our insights from the reeler mutant mouse, a model for a developmental, "molecular lesion"-induced loss of cortical layering that could serve as ground truth of what an intact layering adds to the cortex in terms of functionality. We could demonstrate that the reeler neocortex shows no inversion of cortical layers but rather a severe disorganization that in the primary somatosensory cortex leads to the complete loss of layers. Nevertheless, the somatosensory system is well organized. When exploring an enriched environment with specific sets of whiskers, activity-dependent gene expression takes place in the corresponding modules. Precise whisker stimuli lead to the functional activation of somatotopically organized barrel columns as visualized by intrinsic signal optical imaging. Similar results were obtained in the reeler visual system. When analyzing pathways that could be responsible for preservation of tactile perception, lemniscal thalamic projections were found to be largely intact, despite the smearing of target neurons across the cortical mantle. However, with optogenetic experiments we found evidence for a mild dispersion of thalamic synapse targeting on layer IV-spiny stellate cells, together with a general weakening in thalamocortical input strength. This weakening of thalamic inputs was compensated by intracortical mechanisms involving increased recurrent excitation and/or reduced feedforward inhibition. In conclusion, a layer loss so far only led to the detection of subtle defects in sensory processing by reeler mice. This argues in favor of a view in which cortical layers are not an essential component for basic perception and cognition. A view also supported by recent studies in birds, which can have remarkable cognitive capacities despite the lack of a neocortex with multiple cortical layers. In conclusion, we suggest that future studies directed toward understanding cortical functions should rather focus on circuits specified by functional cell type composition than mere laminar location. [ABSTRACT FROM AUTHOR]

Purpose To determine if loss of the swallow tail sign (STS) can distinguish Parkinson Disease (PD) from the Parkinson-Plus syndromes. Methods Twenty-five patients with PD, 21 with Parkinson-Plus syndromes, and 14 control patients were included. Presence of the STS was assessed. Results The STS was present in 79% of controls, statistically greater than the PD/Parkinson-Plus patients. There was no difference in the presence of the STS between the PD/Parkinson-Plus subgroups or when scanning at 1.5 T or 3 T. Conclusions Loss of the STS could not distinguish between PD and Parkinson-Plus patients. The STS can be identified at both 1.5 T and 3 T. [ABSTRACT FROM AUTHOR]

We present the case of a 33-year-old man who experienced a 10,000-V electrical shock when working with electrical wiring. He suffered third-degree burns on his scalp at the right occiput (entry wound) and on his left arm (exit would), and a second-degree burn on his left foot (exit wound). He presented with severe spasticity of both lower extremities, motor weakness with a Medical Research Council grade of 3, and sensory impairments below thoracic level 11 that included an inability to sense light touch and defects in proprioception. Initial magnetic resonance imaging (MRI) scans of his spine and brain showed no definite abnormalities. However, tractography obtained by diffusion tensor imaging of the brain showed absence of the right medial lemniscus tract. A cervical MRI scan 1 month later showed spinal cord swelling from cervical 1-5 levels, and signal changes in the lateral and posterior white matter in the axial view. After 6 months of rehabilitation, he recovered almost normal degree of motor function in his lower extremities and disappearance of spasticity. However, since the sensory impairments persisted, especially defects in proprioception, he was unable to walk independently. [ABSTRACT FROM AUTHOR]

Objective Thalamopeduncular tumors (TPTs) of childhood present a challenge for neurosurgeons due to their eloquent location. Preoperative fiber tracking provides total or near-total resection, without additional neurologic deficit. High-definition fiber tractography (HDFT) is an advanced white matter imaging technique derived from magnetic resonance imaging diffusion data, shown to overcome the limitations of diffusion tensor imaging. We aimed to investigate alterations of corticospinal tract (CST) and medial lemniscus (ML) caused by TPTs and to demonstrate the application of HDFT in preoperative planning. Methods Three pediatric patients with TPTs were enrolled. CSTs and MLs were evaluated for displacement, infiltration, and disruption. The relationship of these tracts to tumors was identified and guided surgical planning. Literature was reviewed for publications on pediatric thalamic and TPTs that used diffusion imaging. Results Two patients had histologic diagnosis of pilocytic astrocytoma. One patient whose imaging suggested a low-grade glioma was managed conservatively. All tracts were displaced (1 CST anteriorly, 2 CSTs, 1 ML anteromedially, 1 ML medially, and 1 ML posteromedially). Literature review revealed 2 publications with 15 pilocytic astrocytoma cases, which investigated CST only. The condition of sensory pathway or anteromedial displacement of the CST in these tumors was not reported previously. Conclusions Displacement patterns of the perilesional fiber bundles by TPTs are not predictable. Fiber tracking, preferably HDFT, should be part of preoperative planning to achieve maximal extent of resection for longer survival rates in this young group of patients, while preserving white matter tracts and thus quality of life. [ABSTRACT FROM AUTHOR]

Objective The use of diffusion kurtosis imaging (DKI) and diffusion tensor imaging (DTI) was evaluated in assessing cochlear nerve deficiency (CND) and its effect on normal maturation of auditory tract. Methods 25 CND patients and 25 controls (age matched: 2 months to 17 years, gender matched) were evaluated by mean kurtosis (MK), axial kurtosis, and radial kurtosis and compared against fractional anisotropy (FA), axial and radial diffusivities in internal auditory canal (IAC), lateral lemniscus (LL) and inferior colliculus (IC). The age related changes of auditory tract were studied through Pearson correlation between estimated indices and age of both CND and control populations. Results Significant loss of MK (IAC: 10.71%, IC: 10.87%, LL: 15.63%) was observed in CND cases as against moderate reduction in FA (IAC: 8.57%, IC: 10%, LL: 7.69%) in all three anatomical locations. Similarly, substantial decline is observed in radial kurtosis (IAC: 27.03%, IC: 33.33%, LL: 31.43%) in comparison to moderate increase in radial diffusivity (IAC: 13.46%, IC: 24.39%, LL: 24%) in CND cases. No statistically significant change was seen in both axial kurtosis and diffusivities. In control populations, MK (r = 0.473, p = 0.011) and radial kurtosis (r = 0.418, p = 0.016) correlate positively with age and had no correlation in case of CND cases. FA (r = 0.356, p = 0.019) minimally correlated with age in control population but showed no statistically significant correlation in CND cases (r = 0.198, p = 0.036). Conclusion DKI metrics performed better than DTI in assessing microstructural changes of CND. In particular, MK and radial kurtosis are found to be more sensitive enough to differentiate the normal maturation of cochlear nerve from CND cases. [ABSTRACT FROM AUTHOR]

Electrical stimulation of the dorsal columns (DCs; spinal cord stimulation; SCS) has been proposed to treat chronic neuropathic pain. SCS may activate a dual mechanism that would affect both the spinal cord and supraspinal levels. Stimulation of DCs or DC nuclei (DCN) in animals where neuropathic pain has been induced causes activation of brainstem centers including the periaqueductal gray (PAG), which is involved in the endogenous pain suppression system. Biotinylated dextran-amine (BDA) was iontophoretically injected into the DCN to analyze the ascending projection directed to the PAG. Separate injections into the gracile nucleus (GrN) and the cuneate nucleus (CunN) showed BDA-positive fibers terminating in different regions of the contralateral PAG. GrN-PAG afferents terminated in the caudal and middle portions of PAG-l, whereas CunN-PAG fibers terminated in the middle and rostral portions of PAG-l. Based on the DCN somatotopic map, the GrN sends information to the PAG from the contralateral hindlimb and the tail and the CunN from the contralateral forelimb, shoulder, neck and ear. This somatotopic organization is consistent with earlier electrophysiological and PAG stimulation studies. These fibers could form part of the DCs-brainstem-spinal cord loop, which may be involved in the inhibitory effects of SCS on neuropathic pain. [ABSTRACT FROM AUTHOR]

Auditory information relayed by auditory nerve fibers and somatosensory information relayed by granule cell parallel fibers converge on the fusiform cells (FCs) of the dorsal cochlear nucleus, the first brain station of the auditory pathway. In vitro, parallel fiber synapses on FCs exhibit spike-timing-dependent plasticity with Hebbian learning rules, partially mediated by the NMDA receptor (NMDAr). Well-timed bimodal auditorysomatosensory stimulation, in vivo equivalent of spike-timing-dependent plasticity, can induce stimulus-timing-dependent plasticity (StTDP) of the FCs spontaneous and toneevoked firing rates. In healthy guinea pigs, the resulting distribution of StTDP learning rules across a FC neural population is dominated by a Hebbian profile while anti- Hebbian, suppressive and enhancing LRs are less frequent. In this study, we investigate in vivo, the NMDAr contribution to FC baseline activity and long term plasticity. We find that blocking the NMDAr decreases the synchronization of FC- spontaneous activity and mediates differential modulation of FC rate-level functions such that low, and high threshold units are more likely to increase, and decrease, respectively, their maximum amplitudes. Three significant alterations in mean learning-rule profiles were identified: transitions from an initial Hebbian profile towards (1) an anti-Hebbian; (2) a suppressive profile; and (3) transitions from an anti-Hebbian to a Hebbian profile. FC units preserving their learning rules showed instead, NMDAr-dependent plasticity to unimodal acoustic stimulation, with persistent depression of tone-evoked responses changing to persistent enhancement following the NMDAr antagonist. These results reveal a crucial role of the NMDAr in mediating FC baseline activity and long-term plasticity which have important implications for signal processing and auditory pathologies related to maladaptive plasticity of dorsal cochlear nucleus circuitry. [ABSTRACT FROM AUTHOR]

The ventral nucleus of the lateral lemniscus (VNLL) provides a major inhibitory projection to the inferior colliculus (IC). Neurons in the VNLL respond with various firing patterns and different temporal precision to acoustic stimulation. The present study investigates the underlying intrinsic and synaptic properties of various cell types in different regions of the VNLL, using in vitro electrophysiological recordings from acute brain slices of mice and immunohistochemistry. We show that the biophysical membrane properties and excitatory input characteristics differed between dorsal and ventral VNLL neurons. Neurons in the ventral VNLL displayed an onset-type firing pattern and little hyperpolarization-activated current (Ih). Stimulation of lemniscal inputs evoked a large all-or-none excitatory response similar to Calyx of Held synapses in neurons in the lateral part of the ventral VNLL. Neurons that were located within the fiber tract of the lateral lemniscus, received several and weak excitatory input fibers. In the dorsal VNLL onsettype and sustained firing neurons were intermingled. These neurons showed large Ih and were strongly immunopositive for the hyperpolarization-activated cyclic nucleotidegated channel 1 (HCN1) subunit. Both neuron types received several excitatory inputs that were weaker and slower compared to ventrolateral VNLL neurons. Using a mouse model that expresses channelrhodopsin under the promotor of the vesicular GABA transporter (VGAT) suggests that dorsal and ventral neurons were inhibitory since they were all depolarized by light stimulation. The diverse membrane and input properties in dorsal and ventral VNLL neurons suggest differential roles of these neurons for sound processing. [ABSTRACT FROM AUTHOR]

Agreeing with Damasio's statement defining the "process" of consciousness, we propose the self as created by mind-based knowledge and a combination of images of an organism's intentional motor responses interacting with its environment. The lemniscal system, with plastic capabilities, manages gravity in voluntary movement. The spinal segment motor reflex represents the schema of gravity-managing neuronal activity, and it can become "nested" in cortical areas participating in consciousness-building, allowing consideration of the brain as a hyper-evolved nervous system segment harboring atavic spinal organization. Consciousness' capability to change itself makes humans co-participants in their own mental and consciousness evolution. [ABSTRACT FROM AUTHOR]

We investigated differences of the medial lemniscus and its thalamocortical pathway (ML), and the spinothalamic tract and its thalamocortical pathway (STT) according to the cortical termination areas. We found that the ML and STT terminated in the motor cortex and the somatosensory cortex. The ML may be closely related to the motor cortex for motor planning and execution, while the STT may be closely related to the cerebral cortex for somatosensory function and motor execution. [ABSTRACT FROM PUBLISHER]

In vivo intracellular responses to auditory stimuli revealed that, in a particular population of cells of the ventral nucleus of the lateral lemniscus (VNLL) of rats, fast inhibition occurred before the first action potential. These experimental data were used to constrain a leaky integrate-and-fire (LIF) model of the neurons in this circuit. The post-synaptic potentials of the VNLL cell population were characterized using a method of triggered averaging. Analysis suggested that these inhibited VNLL cells produce action potentials in response to a particular magnitude of the rate of change of their membrane potential. The LIF model was modified to incorporate the VNLL cells’ distinctive action potential production mechanism. The model was used to explore the response of the population of VNLL cells to simple speech-like sounds. These sounds consisted of a simple tone modulated by a saw tooth with exponential decays, similar to glottal pulses that are the repeated impulses seen in vocalizations. It was found that the harmonic component of the sound was enhanced in the VNLL cell population when compared to a population of auditory nerve fibers. This was because the broadband onset noise, also termed spectral splatter, was suppressed by the fast onset inhibition. This mechanism has the potential to greatly improve the clarity of the representation of the harmonic content of certain kinds of natural sounds. [ABSTRACT FROM AUTHOR]

Response adaptation is associated with attenuation of neural responses as the result of different mechanisms. However, the main function of adaptation may be to enhance the flow of relevant information transmission in sensory pathways. To study tactile response adaptation in the somatosensory pathway, unit recordings were performed in the principal trigeminal nucleus, ventro postero-medial thalamic nucleus and barrel cortex by means of tungsten microelectrodes in urethane anesthetized rats. Tactile stimuli consisted in 20 ms duration whisker deflections at different frequencies (0.5–10 Hz). Presumably pyramidal cortical neurons showed response adaptation at frequencies >2 Hz while putative inhibitory cortical neurons did not show response adaptation at 0.5, 5 or 10 Hz. Inhibitory activity was increased by muscimol application into the cortex (8 mM, 0.1 µl); in this condition cortical adaptation was not affected, suggesting that adaptation was not due to an increase of inhibitory mechanisms. Adaptation was also observed in subcortical structures although the response attenuation was lesser than in the barrel cortex. Adaptation remained in subcortical structures after reversible cortical inactivation by cooling the barrel cortex. Acetylcholine application (10 μM; 0.1 μl) into the barrel cortex reduced response adaptation through the activation of muscarinic receptors because the effect was blocked by intraperitoneal injection of atropine (1 mg/kg), suggesting that adaptation may change according to the cortical Ach level. Results indicate that response adaptation increases along the somatosensory pathway probably to alter the sensitivity of neurons in order to encode sensory stimuli more efficiently and to enhance the detectability of rare stimuli. [ABSTRACT FROM AUTHOR]

Using 11.7 T ultra high-field T2-weighted MRI, the present study aimed to investigate pathological changes of primary and secondary trigeminal pathways following neonatal transection of infraorbital nerve in rats. The trigeminal pathways consist of spinal trigeminal tract, trigeminal sensory nuclear complex, medial lemniscus, ventromedial portion of external medullary lamina and ventral posterior nucleus of thalamus. By selecting optimum parameters of MRI such as repetition time, echo time, and slice orientation, this study visualized the trigeminal pathways in rats without any contrast agents. Pathological changes due to the nerve transection were found at 8 weeks of age as a marked reduction of the areas of the trigeminal pathways connecting from the injured nerve. In addition, T2-weighted MR images of the trigeminal nerve trunk and the spinal trigeminal tract suggest a communication of CSF through the trigeminal nerve between the inside and outside of the brain stem. These results support the utility of ultra high-field MRI system for noninvasive assessment of effects of trigeminal nerve injury upon the trigeminal pathways. [ABSTRACT FROM AUTHOR]

Objective To investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg). Methods Twenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation. Results SEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05 ± 0.61 ms) shifted of 0.18 ± 0.07 ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4 ± 0.2 ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials. Conclusion While the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level. Significance Our results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area. [ABSTRACT FROM AUTHOR]

Experiments in several species have identified direct projections to the medial geniculate nucleus (MG) from cells in subcollicular auditory nuclei. Moreover, many cochlear nucleus cells that project to the MG send collateral projections to the inferior colliculus (IC) (Schofield et al., 2014). We conducted three experiments to characterize projections to the MG from the superior olivary and the lateral lemniscal regions in guinea pigs. For experiment 1, we made large injections of retrograde tracer into the MG. Labeled cells were most numerous in the superior paraolivary nucleus, ventral nucleus of the trapezoid body, lateral superior olivary nucleus, ventral nucleus of the lateral lemniscus, ventrolateral tegmental nucleus, paralemniscal region and sagulum. Additional sources include other periolivary nuclei and the medial superior olivary nucleus. The projections are bilateral with an ipsilateral dominance (66%). For experiment 2, we injected tracer into individual MG subdivisions. The results show that the subcollicular projections terminate primarily in the medial MG, with the dorsal MG a secondary target. The variety of projecting nuclei suggest a range of functions, including monaural and binaural aspects of hearing. These direct projections could provide the thalamus with some of the earliest (i.e., fastest) information regarding acoustic stimuli. For experiment 3, we made large injections of different retrograde tracers into one MG and the homolateral IC to identify cells that project to both targets. Such cells were numerous and distributed across many of the nuclei listed above, mostly ipsilateral to the injections. The prominence of the collateral projections suggests that the same information is delivered to both the IC and the MG, or perhaps that a common signal is being delivered as a preparatory indicator or temporal reference point. The results are discussed from functional and evolutionary perspectives. [ABSTRACT FROM AUTHOR]

Besides the rapid fluctuations in pressure that constitute the "fine structure" of a sound stimulus, slower fluctuations in the sound's envelope represent an important temporal feature. At various stages in the auditory system, neurons exhibit tuning to envelope frequency and have been described as modulation filters. We examine such tuning in the ventral nucleus of the lateral lemniscus (VNLL) of the pentobarbital-anesthetized cat. The VNLL is a large but poorly accessible auditory structure that provides a massive inhibitory input to the inferior colliculus. We test whether envelope filtering effectively applies to the envelope spectrum when multiple envelope components are simultaneously present. We find two broad classes of response with often complementary properties. The firing rate of onset neurons is tuned to a band of modulation frequencies, over which they also synchronize strongly to the envelope waveform. Although most sustained neurons show little firing rate dependence on modulation frequency, some of them are weakly tuned. The latter neurons are usually band-pass or low-pass tuned in synchronization, and a reverse-correlation approach demonstrates that their modulation tuning is preserved to nonperiodic, noisy envelope modulations of a tonal carrier. Modulation tuning to this type of stimulus is weaker for onset neurons. In response to broadband noise, sustained and onset neurons tend to filter out envelope components over a frequency range consistent with their modulation tuning to periodically modulated tones. The results support a role for VNLL in providing temporal reference signals to the auditory midbrain. [ABSTRACT FROM AUTHOR]

Objective To demonstrate that the trajectory for targeting the Pedunculopontine Tegmental Nucleus (PPTg) is safe. Methods Ten patients, suffering from Parkinson disease underwent electrode implantation in the PPTg for neuromodulation. Median and tibial nerve somatosensory evoked potentials (SEPs) were recorded in all the patients before and after PPTg targeting. Five patients were studied in our laboratory before and after surgery (group I). In the remaining 5 patients, SEPs were recorded in the operating room before and immediately after the PPTg targeting (group II). Results After PPTg targeting, the scalp tibial nerve SEP amplitudes were decreased of 42% and 74% in Group I and Group II patients, respectively. SEP amplitudes recovered within 10 days. Median nerve SEPs were not affected by implantation. Conclusions Tibial nerve SEP amplitude decrease after PPTg targeting was probably due to microlesions in the lateral part of the medial lemniscus including fibers originating from lower limb. The quick recover demonstrates that a partial neurapraxic block of the nerve conduction is likely to occur. Key message Our results suggest that the stereotactic procedure for targeting the PPTg represents a safe trajectory. [ABSTRACT FROM AUTHOR]

Summary A new study describes a novel passive integration mechanism of inhibition in auditory neurons in the dorsal nucleus of the lateral lemniscus that turns extremely well-timed synaptic events into a signal code that is three orders of magnitude slower. [ABSTRACT FROM AUTHOR]

To demonstrate that the trajectory for targeting the Pedunculopontine Tegmental Nucleus (PPTg) is safe. Ten patients, suffering from Parkinson disease underwent electrode implantation in the PPTg for neuromodulation. Median and tibial nerve somatosensory evoked potentials (SEPs) were recorded in all the patients before and after PPTg targeting. Five patients were studied in our laboratory before and after surgery (group I). In the remaining 5 patients, SEPs were recorded in the operating room before and immediately after the PPTg targeting (group II). After PPTg targeting, the scalp tibial nerve SEP amplitudes were decreased of 42% and 74% in Group I and Group II patients, respectively. SEP amplitudes recovered within 10 days. Median nerve SEPs were not affected by implantation. Tibial nerve SEP amplitude decrease after PPTg targeting was probably due to microlesions in the lateral part of the medial lemniscus including fibres originating from lower limb. The quick recover demonstrates that a partial neurapraxic block of the nerve conduction is likely to occur. Our results suggest that the stereotactic procedure for targeting the PPTg represents a safe trajectory. [ABSTRACT FROM AUTHOR]

To define the extent of damage caused by an ischemic lesion of the left midlateral upper medulla in a 75 year-old patient we performed extensive neurophysiological assessment including somatosensory- and laser-evoked potentials from the upper limbs, exteroceptive and nociceptive blink reflex (tested using a concentric planar electrode), masseter inhibitory reflex and trigeminal laser-evoked potentials. Cutaneous laser stimulation of the right hand failed to evoke any cortical response; somatosensory evoked potentials, exteroceptive and nociceptive blink reflex, masseter inhibitory reflex, and trigeminal laser-evoked potentials were normal on both sides. Neurophysiological data proved the involvement of the left spinothalamic tract and the sparing of the trigeminal descending nucleus, ventral secondary ascending trigeminal pathways, and dorsal column-medial lemniscus sensory pathway. Neurophysiological findings, along with clinical and instrumental evidence of ipsilateral palatolaryngeal palsy indicating damage of the nucleus ambiguous, allow the diagnosis of Avellis’ syndrome, a rare brainstem syndrome originally described in 1891. Routine use of neurophysiological techniques provides precise identification of the neural structures involved in small medullary syndromes, thus refining diagnosis and favouring a precise identification of the vascular territory involved. [ABSTRACT FROM AUTHOR]