Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Sensorimotor Cortex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77Linked to original sources
PubMed1982

The motor cortex of the rat: cytoarchitecture and microstimulation mapping.

The first motor (MI) cortex of the rat was identified as the region from which movements could be evoked by the lowest intensity of electrical stimulation. The location of this region was correlated with cytoarchitecture in the frontal and parietal cortex. Two frontal areas can be discerned in Nissl-stained sections: (1) the medial agranular field, marked by a pale-staining layer III and a compact layer II, and (2) the lateral agranular field, which has more homogeneous superficial layers and a broad layer V containing large, densely staining cells. Both of these regions project to the spinal cord and can therefore be included in the somatic sensorimotor cortex. MI in the rat coincides with the lateral agranular field but also overlaps with part of the adjacent granular cortex of the first somatic sensory (SI) representation. We conclude that the rat MI cortex can be identified by microstimulation techniques and by cytoarchitecture in the rat.

Animals↗
PubMed1995

Principal component analysis and the scaled subprofile model compared to intersubject averaging and statistical parametric mapping: I. "Functional connectivity" of the human motor system studied with [15O]water PET.

Using [15O]water PET and a previously well studied motor activation task, repetitive finger-to-thumb opposition, we compared the spatial activation patterns produced by (1) global normalization and intersubject averaging of paired-image subtractions, (2) the mean differences of ANCOVA-adjusted voxels in Statistical Parametric Mapping, (3) ANCOVA-adjusted voxels followed by principal component analysis (PCA), (4) ANCOVA-adjustment of mean image volumes (mean over subjects at each time point) followed by F-masking and PCA, and (5) PCA with Scaled Subprofile Model pre- and postprocessing. All data analysis techniques identified large positive focal activations in the contralateral sensorimotor cortex and ipsilateral cerebellar cortex, with varying levels of activation in other parts of the motor system, e.g., supplementary motor area, thalamus, putamen; techniques 1-4 also produced extensive negative areas. The activation signal of interest constitutes a very small fraction of the total nonrandom signal in the original dataset, and the exact choice of data preprocessing steps together with a particular analysis procedure have a significant impact on the identification and relative levels of activated regions. The challenge for the future is to identify those preprocessing algorithms and data analysis models that reproducibly optimize the identification and quantification of higher-order sensorimotor and cognitive responses.

Adult↗
PubMed1997

FMRI studies of the supplementary motor area and the premotor cortex.

Brain activation patterns associated with three motor tasks, differing in the mode of movement selection, were studied in seven right-handed subjects, using functional magnetic resonance imaging (fMRI). The tasks consisted of sequences of finger movements in which the next finger was selected (i) according to a fixed sequence (FIX), (ii) in response to an external sensory cue (RAND), or (iii) on the basis of free, internal selection (SELF). Periods of hand relaxation (REST) alternating with the tasks served as a control. Functional maps resulting from comparison of the motor tasks with REST reveal activation in primary sensorimotor cortex, medial and lateral premotor areas, cingulate cortex, and parietal cortex. The task activation level, defined as the percentage MR signal increase for each task relative to REST, and the differential activation, defined as the percentage MR signal increase for RAND and SELF relative to FIX, were calculated in each area. All areas showed a higher activation level for RAND and SELF than for FIX. A significant difference in activation level or differential activation between SELF and RAND was found in the posterior part of the superior frontal sulcus, in a part of the premotor cortex on the lateral brain surface, in the anterior cingulate motor cortex, and in the posterior part of the superior parietal cortex. The high-resolution and single-subject approach, provided by fMRI, allowed the distinguishing of multiple foci in medial frontal areas, premotor cortex, and parietal cortex, reflecting the functional heterogeneity of these areas suggested by previous studies.

Adult↗
PubMed2006

Coherence analysis differentiates between cortical myoclonic tremor and essential tremor.

Familial cortical myoclonic tremor with epilepsy (FCMTE) is characterized by a distal kinetic tremor, infrequent epileptic attacks, and autosomal dominant inheritance. The tremor is thought to originate from the motor cortex. In our patient group, a premovement cortical spike could not be established on electroencephalogram (EEG) back-averaging. Corticomuscular and intermuscular coherence analysis can demonstrate a cortical common drive to muscles. We carried out coherence analysis of electromyography (EMG) of forearm muscles and EEG of contralateral motor cortex in 7 FCMTE patients, 8 essential tremor (ET) patients, and 7 healthy controls. Results showed strong cortico- and intermuscular coherence in the 8- to 30-Hz range in the FCMTE patients, with EEG preceding EMG. Healthy controls and ET patients showed normal weak coherence around 20 Hz. The ET patients showed some additional coherence at tremor frequency (6 Hz), probably the result of sensory information flowing back to the sensorimotor cortex. These findings point to a pathological cortical drive in FCMTE patients leading to tremulous movements. Coherence analysis is an easy and useful method to differentiate FCMTE from ET. Coherence analysis is helpful when investigating a cortical common drive in cortical tremor and other movement disorders.

Adult↗
PubMed2003

Asymmetry in the human primary somatosensory cortex and handedness.

Brain asymmetry is a phenomenon well known for handedness and language specialization and has also been studied in motor cortex. Less is known about hemispheric asymmetries in the somatosensory cortex. In the present study, we systematically investigated the representation of somatosensory function analyzing early subcortical and cortical somatosensory-evoked potentials (SEP) after electrical stimulation of the right and left median nerve. In 16 subjects, we compared thresholds, the peripheral neurogram at Erb point, and, using MRI-based EEG source analysis, the P14 brainstem component as well as N20 and P22, the earliest cortical responses from the primary sensorimotor cortex. Handedness was documented using the Edinburgh Inventory and a dichotic listening test was performed as a measure for language dominance. Whereas thresholds, Erb potential, and P14 were symmetrical, amplitudes of the cortical N20 showed significant hemispheric asymmetry. In the left hemisphere, the N20 amplitude was higher, its generator was located further medial, and it had a stronger dipole moment. There was no difference in dipole orientation. As a possible morphological correlate, the size of the left postcentral gyrus exceeded that of the right. The cortical P22 component showed a lower amplitude and a trend toward weaker dipole strength in the left hemisphere. Across subjects, there were no significant correlations between laterality indices of N20, the size of the postcentral gyrus, handedness, or ear advantage. These data show that asymmetry of median nerve SEP occurs at the cortical level, only. However, both functional and morphological cortical asymmetry of somatosensory representation appears to vary independently of motor and language functions.

Adult↗
PubMed2000

Cerebral correlates of working memory for temporal information.

Studies of neural correlates of working memory functions in the auditory-verbal, visuo-spatial and visuo-object domain suggest a category-specific organization of working memory processes in prefrontal cortex. Here, we used fMRI to explore brain areas that underlie different working memory operations directed to the temporal domain, which so far has been widely neglected. Significant activations related to memory updating and comparison processes were found right-accentuated in prefrontal and lateral premotor cortices. Furthermore, both subvocal rhythm encoding and maintenance enhanced left-lateralized activity in Broca's and supplementary motor area as well as in the sensorimotor cortex. Hemispheric lateralization effects of brain activity during temporal processing tasks may depend on the presence or absence of subvocal rehearsal strategies.

Adult↗
PubMed2006

Parallel stages of learning and recovery of skilled reaching after motor cortex stroke: "oppositions" organize normal and compensatory movements.

Forelimb/hand motor cortex injury in rodents and primates causes impairments in skilled paw/hand movements that includes a period of movement absence followed by functional recovery/compensation. Although the postsurgical period of movement absence has been attributed to "shock" or "diaschisis", the behavior of animals during this period has not been fully described. Here, rats were trained to reach for single food pellets from a shelf and then the vasculature of the forelimb region of the sensorimotor cortex contralateral to the reaching limb was removed. A control group received a posterior parietal cortex devasularization. Frame-by-frame video analysis of reaching behavior showed that the stages of the acquisition of skilled reaching and the stages of recovery after motor cortex stroke were similar. The animals sequentially learn three relationships or "oppositions" between a body part and the food target. The oppositions are invariant relationships but each can be achieved with movements that can vary from reach to reach and between rats. A snout-pellet opposition organizes the movements of orienting, a paw-pellet opposition organizes limb transport and grasping the pellet in the digits, and a mouth-pellet opposition organizes limb withdrawal and the release of the food into the mouth. The three oppositions and the movements that they recruit were disrupted after motor cortex damage, but not parietal cortex damage. The oppositions were reestablished after stroke in the order in which they were acquired prior to stroke. Enduring impairments were more noticeable in transport and withdrawal oppositions. That the stages of recovery from motor cortex stroke parallel those of initial acquisition are discussed in relation to contemporary explanations of diaschisis and the contribution of motor cortex to motor learning.

Analysis of Variance↗
PubMed2001

Exercise increases metabolic capacity in the motor cortex and striatum, but not in the hippocampus.

Acute bouts of exercise have been shown to produce transient increases in regional cerebral glucose utilization, oxygen uptake, and cerebral blood flow in motor cortex, striatum, and hippocampus. The purpose of this study was to determine whether or not chronic exercise will cause long-term metabolic plasticity in brain structures activated during physical activity. The activity of cytochrome oxidase (COX), is coupled to the production of ATP, and reflects long-term plasticity in metabolic capacity. The present study examined whether or not 6 months of voluntary exercise would increase COX activity in the striatum, sensorimotor cortex, and three hippocampal subfields. Five-month-old, female Long-Evans hooded rats were randomly assigned to a control or exercise condition. Exercising rats had running wheels attached to their home cages. After the training period, fresh brains were rapidly frozen and sectioned with a cryostat. COX activity was measured using COX histochemical methods and optical densitometry. Rats in the exercise condition had significantly higher optical density in the hindlimb and forelimb motor cortices (18%, P<0.01) and dorsolateral caudate putamen (17%, P<0.01), but not in the ventrolateral caudate putamen or any subfield of the hippocampus. Although exercise is believed to increase neuronal activity in the hippocampus, motor cortex and striatum, only limb representations in the motor cortex and striatum increase bioenergetic capacity after regular exercise.

Animals↗
PubMed2003

Vagal input to lateral area 3a in cat cortex.

Penfield's sensory homunculus included visceral organs at its lateral extreme, and vagal input was recently identified lateral to the intraoral representation in primary somatosensory cortex (S1) of rats. We tested whether vagal input is similarly located in cats where area 3b (equivalent to S1) is clearly distinguishable from adjacent regions. Field potentials were recorded from the intact dura over the left hemisphere using electrical stimulation of the left or right cervical vagus nerve in seven cats. A surface positive-negative potential was evoked from either side in the lateral part of the sigmoid gyrus. Finer mapping made at the pial surface with a microelectrode identified a focal site anteromedial to the anterior tip of the coronal sulcus. Depth recordings demonstrated polarity reversals and multi-unit vagal responses, indicating that the potentials were generated by an afferent activation focus in the middle layers of the cortex. The S1 mechanoreceptive representation was localized by mapping multi-unit somatosensory receptive fields in the middle cortical layers near the coronal sulcus. The vagal-evoked potential site was distinctly anterior to the intraoral S1 representation and adjacent to the masseteric-nerve-evoked potential focus. Lesions made at the focal site revealed that this site is cytoarchitectonically located in area 3a not area 3b. Thus vagal input to the sensorimotor cortex in cats resembles deep rather than cutaneous somatic input, similar to the localization of nociceptive-specific input to area 3a in monkeys. The possibilities are considered that this vagal input is involved in motor control and in the sensory experience of visceral afferent activity.

Animals↗
PubMed2004

Long-term outcome after epilepsy surgery for focal cortical dysplasia.

OBJECT: Reports of outcomes for surgical treatment of cortical dysplasia associated with epilepsy are conflicting due to the inclusion of patients with a wide range of malformations of cortical development. The authors report their experience and the long-term outcome for a subgroup of patients with the histopathological diagnosis of focal cortical dysplasia of Taylor. METHODS: The records of 22 patients with focal cortical dysplasia of Taylor (15 with the balloon-cell type and seven with the nonballoon-cell type) were reviewed. There were 11 female and 11 male patients whose mean age was 26 +/- 17.6 years (mean +/- standard deviation [SD]) at surgery. The details of their epilepsy evaluation and resection were analyzed. Extent of resection was preoperatively planned using information obtained from long-term intracranial monitoring (15 patients) and/or more definitively determined by histopathologically proven clear margins during resection when feasible (12 patients). The mean duration of follow up was 6.3 +/- 5.1 years (mean +/- SD, range 0.5-15.6 years). Risk factors for epilepsy were trauma (seven patients) or meningoencephalitis (one patient); 14 patients (64%) had no obvious risk factors. The mean age at seizure onset was 9.2 years and the mean duration of their epilepsy was 16.1 +/- 9 years. In two patients there were no adverse findings on magnetic resonance (MR) imaging. In 15 patients (68%), the epileptogenic zone identified on long-term intracranial monitoring extended beyond the abnormality observed on MR images. Focal resection (lesion plus margins) was performed in 14 patients (64%), whereas eight (36%) underwent partial/tailored lobectomy. Two patients underwent multiple subpial transections in addition to partial lesionectomy because their lesions involved the sensorimotor cortex. In these two, functional MR imaging confirmed a normal functional anatomy despite the presence of the cortical dysplasia. Eleven (92%) of 12 patients who underwent resection guided by histopathologically proven clear margins and three (43%) of seven patients who underwent histopathologically proven subtotal resection have remained seizure free. Evidence of clear margins was significantly associated with an improved seizure outcome (p = 0.003). Postoperatively, expected deficits included nondisabling visual field defects, which occurred in three patients (14%), and transient sensorimotor deficits, which appeared in five (23%). Two patients had meningitis, which was successfully treated with antibiotics. Overall, 16 patients (73%) are either seizure free (13 patients), have rare nondisabling partial seizures (one patient), or had one seizure after their medication was changed (two patients). Thirteen patients (59%) have discontinued anticonvulsant medications or are being maintained on monotherapy. Of five patients (23%), two have had rare disabling seizures or significant reduction in their seizure frequency (three patients). One patient's seizures have remained the same. CONCLUSIONS: Focal cortical dysplasias are a distinct subgroup of malformations of cortical development and have a favorable outcome after resection. The epileptogenic zone often extends beyond the abnormality found on neuroimaging. Resection of the epileptogenic zone guided by histopathologically proven clear margins is associated with an improved seizure outcome.

Adolescent↗
PubMed1976

Anticipatory activity of motor cortex neurons in relation to direction of an intended movement.

1. Monkeys were trained to 1) hold a handle in a central zone midway between "push" and "pull" while awaiting 2) an instruction telling them how to respond to a subsequent 3) perturbation, which triggered the instructed movement and was followed by 4) a reward if the movement was correct. 2. There were two sorts of instructions: push and pull. When the pull instruction had preceded the perturbation, the monkey responded to the perturbation by pulling, whereas after a push instruction, the monkey responded to the perturbation by pushing. 3. Recordings in pre- and postcentral sensorimotor cortex revealed instruction-induced changes of neuronal activity during the period intervening between the instruction and the perturbation-triggered movement. Effects of the instruction were differential depending on which of the two instructions was given, such differential responses to the instruction being detected in 61% of precentral pyramidal tract neurons (PTNs), 44% of precentral non-PTNs, and 11% of postcentral neurons. 4. Since motor cortex PTN axons end on alpha and gamma motoneurons and on interneurons of the spinal cord, changes of PTN activity with "intention" or "motor set" provide a mechanism for suprasegmental control and presetting of spinal cord reflex excitability specific to the nature of an impending movement.

Animals↗
PubMed1998

[Developmental plasticity of corticospinal projections in the spinal cord gray matter of normal and hemicortectomized rat].

In the previous study we demonstrated in rats that aberrant ipsilateral CST fibers were increased when the cerebral cortex was surgically ablated unilaterally during the neonatal period. Origin of these aberrant fibers was confirmed to involve collateral axons, ramified from their parent axons. In this study, possible plastic change and the critical period for the outgrowth of CST fibers into the spinal cord gray matter in the rat after unilateral (right side) cortical damage at different ages measured in days were examined using anterograde horseradish peroxidase (HRP). HRP was injected into the left sensorimotor cortex in both normal and experimental rats. In the normal control rats, the outgrowth of HRP positive axons into the spinal gray matter was first noticed at 7 day of age in the vicinity of the right dorsal funiculus, and then reached maximal density and extension at 10 and 14 days of age, respectively. From 21 days onwards, the density and extension of HRP positive axons in the gray matter decreased rapidly except in the medial part close to the dorsal funiculus. In rats whose right cerebral cortex were damaged at day 1 of age, the pattern of the outgrowth of HRP positive axons into the right gray matter was much the same as that in age-matched controls. However, significantly different from the control, many HRP positive axons were noted even in the contralateral gray matter. HRP-positive axons in the contralateral left gray matter were also abundant in the rats who sustained cortical damage at 7 and 14 days, but were decreased considerably when the cerebral cortex was damaged at 28 days of age. When damage occurred at 56 days of age, HRP-positive axons did not increase in the left gray matter, indicating that the critical period of axonal plasticity after localized damage was before 4 weeks of age in rats.

Animals↗
PubMed1998

Focal brain injury and its effects on cerebral mantle, neurons, and fiber tracks.

Following a mild cortical impact injury delivered by a piston to the right sensorimotor cortex of the anesthetized rat, we evaluated mantle loss, neuronal changes, and fiber track degeneration by deOlmos silver stains up to 8 weeks after injury. Darkened neurons indicating damage (chromatolysis) occurred widely throughout both hemispheres and were seen from 1 h to 8 weeks after injury. This effect might have occurred from pressure wave damage from piston impact, brain displacement or deafferentation. Cerebral mantle loss was variable but fiber track degeneration related to projection and corticofugal descending tracks associated with the right sensorimotor system was rather constant. Unexpectedly, considerable fiber track degeneration occurred within the cerebellum, especially the inferior vermis. Cells directly under the piston face were surprisingly well-preserved but axon degeneration studies showed that these apparently intact neuronal cell bodies were surrounded by a dense network of degenerating fiber tracks. The intact cells, therefore, may have been functionally cut off from the rest of the brain owing to interruption of their efferents and afferents. The increased susceptibility of axons compared to cell bodies seen with this focal injury is similar to that observed with diffuse brain injury. The early appearing, severe and widespread axon damage we observed suggests that amelioration of focal traumatic brain injury will have to be directed promptly to the preservation of axons as well as cell bodies.

Animals↗
PubMed1993

Influence of prelimbic and sensorimotor cortices on striatal neurons in the rat: electrophysiological evidence for converging inputs and the effects of 6-OHDA-induced degeneration of the substantia nigra.

These studies were designed to investigate whether there are convergent prelimbic and sensorimotor cortical inputs onto striatal neurons in the rat and whether dopaminergic (DA) nigrostriatal fibers regulate these inputs. The influence of the nigrostriatal DA system was assessed in rats with either small or large 6-hydroxydopamine-induced lesions of the substantia nigra. In normal rats 39 out of 74 neurons (52.7%) were excited by stimulation of both the prelimbic and the sensorimotor cortex. No marked change in corticostriatal transmission was evident in rats with small 6-OHDA-induced lesions (defined as 10-35% decrease in [3H]DA uptake in striatal synaptosomes). In rats with large lesions (75-85% decrease in striatal [3H]DA uptake), however, a complete rearrangement of the corticostriatal transmission occurred. This was evident in a decrease of thresholds to obtain cortical responses, by modifications of the discharge properties of striatal neurons receiving input from cortices and by an increase in the number of neurons responding to cortical stimulation. In addition, a significantly higher percentage of striatal neurons responded to stimulation of both prelimbic and sensorimotor cortices in rats with large lesions than in rats with small lesions or in control rats. This data suggests that: (1) no functional separation of prelimbic and sensorimotor cortical inputs occurs in the rat striatum, (2) the nigrostriatal DA system exerts a focusing effect on these inputs, (3) the striatum is actively involved in the integrative processing of descending cortical information.

Animals↗
PubMed1992

A comparison of the electrophysiological properties of morphologically identified cells in layers 5B and 6 of the rat neocortex.

In vitro studies performed in mammalian brain slices have shown that cortical neurons differ in their intrinsic membrane properties. In the rodent cortex these properties are related to a specific cell morphology and synaptic connectivity in some cells but not in others. Due to their small size, little is known about the intrinsic membrane properties of layer 6 cells, however, and it is not clear whether cell morphology is related to electrophysiological properties in this layer. We used a combination of intracellular recording and dye-filling to study the electrophysiological and morphological characteristics of layer 6 cells of the rat sensorimotor cortex in vitro and compared their properties to those of large layer 5B pyramidal cells. Our sample of 24 filled and anatomically reconstructed cells in layer 6 confirms previous Golgi studies that showed them to be a morphologically diverse group consisting of regularly and irregularly oriented pyramidal cells and spiny nonpyramidal cells. Regular layer 6 pyramidal cells differed with respect to the length of their apical dendrites and extent of their axonal arborizations, while irregularly oriented pyramidal cells consisted of sideways or inverted pyramidal cells of variable size and morphology. Spiny nonpyramidal cells included bi-tufted and multi-polar cell types that differed in size and extent of dendritic trees. Many layer 6 cells showed long horizontal axon collaterals in layer 6, and an oblique or vertical projection to layer 4. Stimulation with intracellular constant current pulses revealed that the morphological diversity was mirrored by a similar electrophysiological diversity. Most layer 6 cells were capable of firing trains of action potentials characterized by an initial doublet or triplet followed by a train of single spikes (phasic-tonic mode). The majority of layer 6 cells could fire in either a tonic (single spikes only) mode with low strength current input and a phasic-tonic pattern with higher current strengths. A minority fired either always phasic-tonic or tonic-only spike trains. The size and sequence of spike afterpotentials during low-rate repetitive firing was highly variable in layer 6 cells suggesting that the relative importance of ionic currents responsible for spike repolarization and afterpotentials varied from cell to cell. Subthreshold responses showed prominent inward rectification, while hyperpolarizing "sag" was present in most cells tested. In comparison, large layer 5B pyramidal cells fired either phasic-tonic only or both phasic-tonic and tonic patterns. A minority of cells were capable of firing repetitive bursts, while the remainder fired repetitive single spikes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Linear inverse source estimate of combined EEG and MEG data related to voluntary movements.

A method for the modeling of human movement-related cortical activity from combined electroencephalography (EEG) and magnetoencephalography (MEG) data is proposed. This method includes a subject's multi-compartment head model (scalp, skull, dura mater, cortex) constructed from magnetic resonance images, multi-dipole source model, and a regularized linear inverse source estimate based on boundary element mathematics. Linear inverse source estimates of cortical activity were regularized by taking into account the covariance of background EG and MEG sensor noise. EEG (121 sensors) and MEG (43 sensors) data were recorded in separate sessions whereas normal subjects executed voluntary right one-digit movements. Linear inverse source solution of EEG, MEG, and EEG-MEG data were quantitatively evaluated by using three performance indexes. The first two indexes (Dipole Localization Error [DLE] and Spatial Dispersion [SDis]) were used to compute the localization power for the source solutions obtained. Such indexes were based on the information provided by the column of the resolution matrix (i.e., impulse response). Ideal DLE values tend to zero (the source current was correctly retrieved by the procedure). In contrast, high DLE values suggest severe mislocalization in the source reconstruction. A high value of SDis at a source space point mean that such a source will be retrieved by a large area with the linear inverse source estimation. The remaining performance index assessed the quality of the source solution based on the information provided by the rows of the resolution matrix R, i.e., resolution kernels. The i-th resolution kernels of the matrix R describe how the estimation of the i-th source is distorted by the concomitant activity of all other sources. A statistically significant lower dipole localization error was observed and lower spatial dispersion in source solutions produced by combined EEG-MEG data than from EEG and MEG data considered separately (P < 0.05). These effects were not due to an increased number of sensors in the combined EEG-MEG solutions. They result from the independence of source information conveyed by the multimodal measurements. From a physiological point of view, the linear inverse source solution of EEG-MEG data suggested a contralaterally preponderant bilateral activation of primary sensorimotor cortex from the preparation to the execution of the movement. This activation was associated with that of the supplementary motor area. The activation of bilateral primary sensorimotor cortical areas was greater during the processing of afferent information related to the ongoing movement than in the preparation for the motor act. In conclusion, the linear inverse source estimate of combined MEG and EEG data improves the estimate of movement-related cortical activity.

Dura Mater↗
PubMed2000

Somatosensory evoked high-frequency oscillations recorded directly from the human cerebral cortex.

OBJECTIVE: To elucidate the generator sources of high-frequency oscillations of somatosensory evoked potentials (SEPs), we recorded somatosensory evoked high-frequency oscillations directly from the human cerebral cortex. SUBJECTS AND METHODS: Seven patients, 6 with intractable partial epilepsy and one with a brain tumor, were studied. With chronically implanted subdural electrodes, we recorded SEPs to median nerve stimulation in all patients, and also recorded SEPs to lip and posterior tibial nerve stimulation in one. High-frequency oscillations were recorded using a restricted bandpass filter (500-2000 Hz). RESULTS: For the median nerve oscillations, all oscillation potentials were maximum at the electrodes closest to the primary hand sensorimotor area. Most oscillations were distributed similar to or more diffusely than P20/N20. Some later oscillations after the peak of P20 or N20 were present in a very restricted cortical area similar to P25. We investigated the phase change of each oscillation potential around the central sulcus. One-third of the oscillations showed phase reversal around the central sulcus, while later oscillations elicited in a restricted cortical area did not. High-frequency oscillations to posterior tibial nerve and lip stimulation were also maximum in the sensorimotor areas. Most of the lip oscillations showed phase reversal around the central sulcus, but most of the posterior tibial nerve oscillations did not. CONCLUSION: High-frequency oscillations are generated near the primary sensorimotor area. There are at least two different generator mechanisms for the median nerve high-frequency oscillations. We suspect that most oscillations are derived from the terminal segments of thalamocortical radiations or from the primary sensorimotor cortex close to the generator of P20/N20, and some later oscillations from the superficial cortex close to the generator of P25.

Brain Neoplasms↗
PubMed1990

Sensorimotor cortical lesion effects and treatment with nimodipine.

Rats with unilateral ablations of the sensorimotor cortex and others with control operations were tested for their ability to touch and remove adhesive tape applied to both forelimbs. Half of each group was administered a calcium channel antagonist (nimodipine) for two weeks following the lesions and the other half received vehicle. The rats with lesions showed a bias to remove the ipsilateral stimulus first and exhibited contralateral deficits relative to control animals. Nimodipine was shown to reduce the contralateral stimulus removal time when the animals began testing two weeks after surgery, but not when testing began 1 day after surgery and overlapped the period of drug administration. Lesion effects also appeared on tests for neurologic impairment and activity, but nimodipine did not reduce these deficits. These findings indicate that nimodipine has the potential to reduce some deficits after sensorimotor cortical lesions, but that the effects of this drug may be task specific.

Animals↗