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At least 1,675 records · Page 93Linked to original sources
PubMed1992

Suppression of cutaneous perception by magnetic pulse stimulation of the human brain.

We have demonstrated that magnetic pulse stimulation of the sensorimotor cortex suppresses perception of threshold electrical stimuli to the fingers of the contralateral hand. Maximum suppression of perception occurs when the fingers are stimulated 30-90 msec after the magnetic pulse. Thereafter, errors in perception of the cutaneous stimulus decrease to control levels by 300-400 msec after the magnetic pulse. The period of maximum suppression of perception coincides with the period during which cortically generated somatosensory evoked potentials (SEPs) are enhanced following magnetic pulse stimulation of the brain. The duration of suppression of perception, however, outlasts the duration of SEP enhancement. When the magnetic pulse is delivered after finger stimulation there is also suppression of perception. The suppression of perception is maximal when the magnetic pulse occurs 20-30 msec after finger stimulation. This interval coincides with the arrival of the afferent volley at the primary sensory cortex.

Electric Stimulation↗
PubMedDate not supplied

The relationship between human long-latency somatosensory evoked potentials recorded from the cortical surface and from the scalp.

In scalp recordings, stimulation of the median nerve evokes a number of long-latency (40-300 msec) somatosensory evoked potentials (SEPs) whose neural origins are unknown. We attempted to infer the generators of these potentials by comparing them with SEPs recorded from the cortical surface or from within the brain. SEPs recorded from contralateral sensorimotor cortex can be characterized as "precentral," "postcentral," or "pericentral." The scalp-recorded P45, N60 and P100 potentials appear to correspond to the pericentral P50, N90 and P190 potentials and are probably generated mainly in contralateral area 1 of somatosensory cortex. The scalp-recorded N70-P70 appear to correspond to the precentral and postcentral N80-P80 and are generated mainly in contralateral area 3b of somatosensory cortex. The scalp-recorded N120-P120 appear to correspond to the intracranial N100-P100 and are probably generated bilaterally in the second somatosensory areas. N140 and P190 (the "vertex potentials") are probably generated bilaterally in the frontal lobes, including orbito-frontal, lateral and mesial (supplementary motor area) cortex. The supplementary sensory area probably generates long-latency SEPs, but preliminary recordings have yet to confirm this assumption. Most of the proposed correspondences are speculative because the different conditions under which scalp and intracranial recordings are obtained make comparison difficult. Human recordings using chronically implanted cortical surface electrodes, and monkey studies of SEPs which appear to be analogs of the human potentials, should provide better answers regarding the precise generators of human long-latency SEPs.

Adolescent↗
PubMedDate not supplied

Enhancement of the amplitude of somatosensory evoked potentials following magnetic pulse stimulation of the human brain.

In this study we have demonstrated an enhancement of cortically generated wave forms of the somatosensory evoked potential (SEP) following magnetic pulse stimulation of the human brain. Subcortically generated activity was unaltered. The enhancement of SEP amplitude was greatest when the median nerve was stimulated 30-70 msec following magnetic pulse stimulation over the contralateral parietal scalp. We posit that the enhancement of the SEP is the result of synchronization of pyramidal cells in the sensorimotor cortex resulting from the magnetic pulse.

Brain↗
PubMed1994

Differentiation of sensorimotor neuronal structures responsible for induction of motor evoked potentials, attenuation in detection of somatosensory stimuli, and induction of sensation of movement by mapping of optimal current directions.

Transcranial magnetic stimulation (TMS) of the sensorimotor cortex can evoke motor evoked potentials (MEPs), attenuation in detection of somatosensory stimuli (ADSS), and sensation of movement (SOM) referred to the same body part. In this study we tried to differentiate the substrates responsible for these effects. In 6 normal volunteers, TMS was applied with a nearly monopolar Dantec stimulator and a butterfly coil. Optimal scalp location and current direction were determined for induction of MEPs in abductor pollicis brevis (APB), first dorsal interosseous (FDI), and adductor digiti minimi (ADM); SOM in digits 2 and 5 in an ischemically paralyzed hand; and ADSS applied to digits 2 and 5. All 3 muscles' MEPs and SOM and ADSS in both digits were optimally activated from a single scalp position. In all subjects, optimal current directions for MEPs pointed anteriorly; those for ADSS and SOM pointed posteriorly. Optimal current directions showed the same progression in all subjects for MEPs (ADM, FDI, and APB from antero-lateral to antero-medial), ADSS (digit 5 postero-medial, 2 postero-lateral), and SOM (digit 1 through 5 postero-lateral to postero-medial). We conclude that neuronal networks targeting corticospinal neurons responsible for MEPs are different from those leading to SOM and ADSS (which could not be differentiated).

Adult↗
PubMed1987

Axons of the pyramidal tract do not increase their transport of growth-associated proteins after axotomy.

We compared the effects of axotomy on the composition of fast axonally transported proteins in rat sciatic sensory axons and pyramidal tract axons, 7 days after axotomy. L-[35S]methionine was administered to dorsal root ganglia or sensorimotor cortex and after 6 or 4 h, respectively, labelled proteins were obtained from sciatic nerve or pyramidal tract. Transported proteins were characterized by one- and two-dimensional electrophoresis, followed by fluorography. As previously reported, sciatic axotomy produced changes in the labelling of fast-transported proteins, notably, increased labelling of a spot designated GAP43. In contrast axotomy of pyramidal axons produced no increased labelling of GAP43, although it could be identified in both normal and axotomized samples. Autoradiography of spinal cord distal to the lesion confirmed that our procedures did indeed label axons and that the axotomy did interrupt these axons. Our finding that axotomy does not stimulate changes in composition of fast-transported proteins in the corticospinal tract agrees with previous studies on mammalian retinal ganglion cell axons and leads us to conclude that this failure to respond to axotomy is a general feature of non-regenerating CNS axons.

Animals↗
PubMed1981

Cerebral potentials during skilled slow positioning movements.

Movement-related potentials recorded from the scalp of man were investigated in two skilled positioning tasks, requiring flexions at different joints of the upper extremities. The average response time was approximately 1 sec. Subjects paced their movements themselves and performed without visual control or other external cues. After each trial a delayed visual feedback was given. It was found that the negative potential shift prior to the EMG onset, the 'Bereitschaftpotential', is followed by a persisting negativity during the execution of the action until the target position is reached. Approximately at this point a positive-going deflection appears. This 'goal-directed movement potential' is composed of at least two components: (a) a widely distributed, centrally dominant negativity, and (b) a smaller negative wave over the sensorimotor cortex contralateral to the responding limb. Small variations in response force do not influence the amplitude of the potentials. A negative shift in anticipation of the visual feedback has a topography different from the movement-related potentials, being predominant over the right hemisphere independent of the hand used

Adult↗
PubMed1980

Is sprouting the result of a persistent neonatal connection?

The present study aims to test the hypothesis that early neonatal connections might account for certain sprouting phenomena in the central nervous system. Fink-Heimer's method for degenerating axons, electron microscopy and autoradiography were used to trace the neonatal corticofugal projections from the sensorimotor cortex (SMC) of albino rats. The results showed that neonatal corticofugal projections to the superior colliculus, red nucleus and spinal cord were unilateral and could not explain the bilateral corticofugal projections to these areas soon after neonatal SMC lesions [8, 10, 12, 13]. The presence of a neonatal contralateral corticopontine projection is also not sufficient to account for the presence of a contralateral corticopontine projection seen after neonatal unilateral SMC lesion, but might account for the contralateral corticopontine projection seen after neonatal unilateral cerebellar hemispherectomy [11].

Age Factors↗
PubMed1983

Retrograde transport of D-[3H]aspartate in thalamocortical neurones.

D-[3H]aspartate (D-Asp) injected into the sensorimotor cortex of the rat resulted in retrograde labelling of thalamic neurones, mainly in the intralaminar and ventromedial nuclei, and the posterior complex. Few cells in the ventrolateral nucleus and ventrobasal complex were labelled. The results show that certain thalamocortical neurones can take up and axonally transport the false transmitter D-Asp, indicating that they might use glutamate or aspartate as transmitter(s).

Animals↗
PubMed1983

Corticofugal influences in the rat on responses of neurons in the trigeminal nucleus interpolaris to mechanical stimulation.

We recorded effects of electrical stimulation of sensorimotor cortex on the responses of 45 neurons in the interpolar trigeminal nucleus to mechanical stimulation of vibrissae. Responses elicited by peripheral mechanical stimulation were enhanced when a neuron's receptive field (RF) included the RF of the cortical stimulating locus, and suppressed when the RFs of the cortical site and the interpolar neuron did not overlap. Several interpolaris neurons influenced by cortical stimulation were shown to project to the cerebellum.

Animals↗
PubMed1984

REM sleep signs rostral to chronic transections at the pontomedullary junction.

The brainstems of 3 cats were transected at the ponto-medullary junction and the cats maintained in stable condition for periods of from 16 to 31 days. After transection, all of these cats had periods in which forebrain sensorimotor cortex, olfactory bulb, hippocampus, eye movement and lateral geniculate recordings exhibited the pattern of activity seen only in REM sleep in the intact cat. We conclude that medullary regions are not required to generate these signs of REM sleep. The pons is necessary for REM sleep and is sufficient to produce REM sleep signs in rostral as well as caudal brain regions. However, the medulla may contribute to regulation of the duration and periodicity of REM sleep.

Animals↗
PubMed1985

Secondary transneuronal degeneration: cortical changes induced by peripheral nerve section in neonatal rats.

Secondary transneuronal degeneration of the cortico-spinal tract (CST) has been induced after sciatic nerve section in newborn rats. Observations made 21-60 days after the lesion showed a considerable decrease in number of myelinated and unmyelinated fibres of the CST ipsilateral to the lesion and of horseradish peroxidase-labelled nerve cells in the somato-sensorimotor cortex of the contralateral cerebral hemisphere. This phenomenon which has never been observed in spite of the frequent studies of experimental peripheral nerve lesions, may be significant in normal and pathological development.

Animals↗
PubMed1990

Reduction of local cerebral blood flow to pathological levels by endothelin-1 applied to the middle cerebral artery in the rat.

Endothelin-1 (1 nmol) was applied to the exposed left middle cerebral artery (MCA) in anaesthetised adult male Sprague-Dawley rats. Local cerebral blood flow (1CBF), using [14C]iodoantipyrine and quantitative autoradiography, was measured in 27 anatomically defined structures, 10 min after topical application of endothelin-1. In those areas supplied by the MCA, 1CBF was markedly reduced beyond the threshold for ischaemic damage (e.g. dorsolateral caudate nucleus reduced from 131 +/- 3 to 29 +/- 25 ml.100 g-1.min-1, sensorimotor cortex from 109 +/- 5 to 31 +/- 21 ml.100 g-1.min-1). Distant areas were not affected.

Animals↗
PubMed1990

Electrocorticographic characterization of chronic iron-induced epilepsy in rats.

Electrocorticograms were recorded from rats which were unilaterally injected with ferrous chloride solution into the sensorimotor cortex to induce chronic epileptic activity. All of the iron-injected rats showed isolated spikes near the injection site and in the contralateral cortex immediately after the injection. The injection produced 3 kinds of responses in the rats according to the frequency of the isolated spikes. Spike and wave complexes appeared bilaterally approximately 30 days or more after the injection in the rats in which the frequency of the isolated spikes was dominant on the side ipsilateral to the injection site or nearly equal on the two sides. These results suggest that there are at least 2 stages in the development of chronic iron-induced epilepsy.

Animals↗
PubMed1991

Synapses formed by ectopic corticofugal axons: an electron microscopic study of crossed corticorubral projections in kittens.

The corticorubral projections in newborn kittens are bilateral, while the projections are unilateral in adults. We addressed the question whether or not the crossed corticorubral projection in kitten forms synaptic contacts in the red nucleus. The neurons in the sensorimotor cortex of the kitten were labeled by Phaseolus vulgaris-leucoagglutinin or biocytin. Electron microscopic observations revealed that corticofugal axons form synapses both in the contralateral and the ipsilateral red nucleus; most of them were on small postsynaptic profiles, possibly dendritic spines or distal dendrites.

Animals↗
PubMed1991

An observation on hitherto unknown corticospinal fibers that descend between the tractus corticospinalis lateralis and ventralis in the cat.

Following injection of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the pericruciate (sensorimotor) cortex on one side in the cat, we found labeled fibers surrounding the ventral horn of the spinal cord bilaterally, in addition to the crossed and the uncrossed lateral, ventral and dorsal corticospinal tracts (CSTs). These hitherto unknown fibers, which could be traced to the caudal end of the L2 segment, were predominantly contralateral to the WGA-HRP injection side. This study indicates the presence of newly recognized CST fibers in the cat.

Animals↗
PubMed1993

Differential action of phenytoin and carbamazepine on cortical interhemispheric responses in young but not in adult rats.

Single as well as paired responses to stimulation of the contralateral sensorimotor cortex were recorded in adult and 12-day-old rats under urethane anesthesia. Carbamazepine (50 mg/kg i.p.) prolonged the peak latencies of single responses in both adult and young rats, while phenytoin (60 mg/kg i.p.) prolonged the latencies in adult animals but shortened them in the young ones. Excitability cycles of the amplitude of the initial positive-negative complex remained uninfluenced by either drug in both age groups. Since solvent alone did not induce any effects in either test, our results demonstrate a qualitative change in the action of phenytoin during development.

Aging↗
PubMed1994

The role of 5-HT1A serotonin and D2 dopamine receptors in buspirone effects on cortical electrical activity in rats.

The effects of buspirone (5 and 10 mg/kg i.p.), 8-OH-DPAT (0.25 mg/kg) and raclopride (2.5 mg/kg) on the EEG power spectra of the sensorimotor cortex were studied in freely moving rats. Buspirone (5 mg/kg) and 8-OH-DPAT produced selective slowing of the theta-activity. Buspirone (10 mg/kg) produced slowing of the theta-activity and increased the power of the alpha-band (9-11 Hz). Raclopride alone did not influence EEG power spectra. Simultaneous injection of 8-OH-DPAT and raclopride produced marked slowing of the theta-activity and increased the power of the alpha-band. The role of 5 HT1A and D2 dopamine receptors in buspirone effects on cortical electrical activity in rats was discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Individual metabolic anatomy of repeating words demonstrated by MRI-guided positron emission tomography.

The anatomical localization of brain areas involved in repeating words was examined in six right-handed non-aphasic subjects. Their individual metabolic activation was studied with positron emission tomography (PET) and [18F]2-fluoro-2-deoxy-D-glucose (FDG) using a new data processing technique that includes three-dimensional coregistration with magnetic resonance images. Left superior temporal gyrus (cortical convexity surface, Brodmann area 22), right superior temporal lobe (superior temporal sulcus and bottom of transverse sulcus), sensorimotor cortex (vocalization area) bilaterally, and supplementary motor cortex were consistently activated in each individual. Cerebellar activation was more variable. In contrast to previous blood flow activation studies with averaging across subjects, this new technique permits the anatomical localization and quantitation of activated areas in each individual. It can therefore also be applied to patients with brain lesions.

Adult↗