Biomedical subjects

H Hummelsheim

Publications and source records attributed to H Hummelsheim.

26 records · Page 2Linked to original sources

PubMed1986

The supplementary motor area modulates perturbation-evoked discharges of neurones in the precentral motor cortex.

The hypothesis was tested that the supplementary motor cortex (SMA) may influence the responsiveness of area 4 neurones to kinesthetic stimuli. In the awake monkey, responses to arm displacements were recorded with and without conditioning intracortical stimulation of the SMA. In 14 of 26 tested area 4 neurones, there was an increase of the response latency and/or a decrease of the response magnitude when the peripheral stimulus was conditioned by SMA stimulation. Field potentials evoked by the displacements were reduced in 3 out of 7 recordings. These findings suggest that the SMA exerts subtle inhibitory effects on the motor cortex or its inputs.

Animals↗

PubMed1986

Further investigations of the efferent linkage of the supplementary motor area (SMA) with the spinal cord in the monkey.

Intracortical microstimulation of the supplementary motor area (SMA) was studied in awake monkeys. With short trains of micropulses, contralateral muscle twitches mainly in shoulder and proximal arm muscles were elicited. There was an indication of a rostro-caudal representation of distal to proximal forelimb, trunk, and proximal to distal hindlimb muscles. However, an intermingling of efferent zones was much more prominent as compared to the precentral motor cortex (MI). All efferent zones to the spinal cord were clustered in the caudal half of the SMA, and we failed to detect face and ocular movements (except at one stimulation site) when microstimulating the rostral portions of the SMA. Single micropulses were also injected in efferent zones of the microexcitable cortex in order to investigate post-pulse facilitation of sustained EMG activity. For motor cortex (MI) stimulation, post-pulse facilitation was prominent and observed in 14 of 17 tested stimulation sites. The incidence of facilitation in comparable muscles obtained with SMA stimulation in comparable muscles obtained with SMA stimulation was only 20 out of 54 tests. The onset latencies of EMG modulation obtained from the two areas were in the same range but the amount of modulation in the SMA was less conspicuous than in MI. These results indicate that the SMA has oligo- or possibly even monosynaptic connections with motoneurones, but that these connections are less dense than those from MI.

Animals↗

PubMed1985

Is the hindlimb representation of the rat's cortex a 'sensorimotor amalgam'?

In the rat, the hindlimb representation of the sensorimotor cortex is characterized by the presence of large pyramids in the fifth layer and a dense granular layer ('sensorimotor amalgam'). The objective was to investigate in the rat, whether or not the efferent zones to the gastrocnemius muscle and the proprioceptive feedback projection from that muscle to the cortex are co-extensive. To this end, the proprioceptive zone was mapped by means of field potentials and single unit discharges evoked by controlled longitudinal displacements of the gastrocnemius tendon. The efferent zones to the gastrocnemius muscle were mapped by means of intracortical microstimulation (ICMS; less than 30 microA). The proprioceptive zone occupied a territory extending from 1.0 to 2.5 mm caudal to the bregma and from 2.0 to 3.0 mm lateral from the midline. The response properties were similar to those observed previously in area 3a of monkeys. For sinusoidal displacements threshold amplitude decreased with increasing stretch frequency. The modal value of response latency was 7 ms, the shortest latency 4 ms. The ICMS zone lay 0.5 to 1.5 mm caudal to bregma having an overlap of 0.5 mm with the proprioceptive region. The proprioceptive as well as the motor areas lay within the granular cortex, but overlapped only to a small extent.

Animals↗

PubMed1985

The projection of low-threshold muscle afferents of the forelimb to the main and external cuneate nuclei of the monkey.

The bulbar relay subserved by primary muscle afferents from the monkey's deep radial nerve was investigated by means of transganglionic labeling with wheatgerm agglutinin conjugated with horseradish peroxidase as well as by electrophysiological techniques. It was found that the "deep" input was confined to the pars triangularis of the main cuneate nucleus and to the ventromedial segment of the external cuneate nucleus. On the other hand, labeling occurring following incubation of the superficial (cutaneous) branch of the radial nerve was limited to the pars rotunda of the main cuneate nucleus. The cytoarchitectonic differentiation of the medullary relays is thus met by a clear-cut submodality segregation.

Afferent Pathways↗

PubMed1985

Neuronal responses of medullary relay cells to controlled stretches of forearm muscles in the monkey.

Single units were recorded extracellularly from the external cuneate nucleus and from the main cuneate nucleus in anesthetized monkeys. The aim was to study the properties of the subpopulation of neurones which transmit "deep" (proprioceptive) information to the thalamus and the cerebral cortex, and to compare the results with previous studies in neurones of the higher "proprioceptive" centres. The neurones were characterized according to their location, their projection to the thalamus and the cerebellum, and their sensitivity to controlled displacements of the extensor digitorum communis muscle. Forty-nine neurones were allocated to the main cuneate nucleus. They occupied the pars triangularis which surrounds the pars rotunda laterally and ventrally. Fifty-six units were classified as external cuneate neurones. Among the external cuneate neurones, 14 neurones were excited antidromically by cerebellar and 8 neurones by thalamic stimulation; two further units responded antidromically to both cerebellar and thalamic stimulation. This observation is in agreement with previous anatomical evidence that part of the external cuneate neurones project to the ventrobasal complex of the thalamus. Possibly, some of these neurones may have bifurcating axons projecting to both targets. More than half of the main cuneate neurones were antidromically excited from the thalamus; three units were backfired from the cerebellum and two units were backfired from both targets. With controlled longitudinal displacements of the extensor digitorum communis tendon, the response patterns of the proprioceptive neurones were similar in both nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1985

Lesions of premotor cortex in man.

Moderate unilateral weakness of shoulder and hip muscles and limb-kinetic apraxia were observed in 11 patients with frontal lobe lesions on the side opposite to the neurological deficits. On the CT scans, the posterior border of the lesions lay anterior to the precentral gyrus, thus involving the premotor cortex but not the primary motor cortex. In 9 cases, the lesions were caused by a brain infarct, in 2 cases by a tumour. In 1 patient the lesion was purely subcortical. Whereas the paresis affected all hip muscles, in the shoulder mainly those movements associated with abduction and elevation of the arm were disturbed. The EMG showed considerable delays for the preactivation of proximal arm muscles during rapid arm movements, thus interfering with the normal proximal-distal sequencing of muscle action. Limb-kinetic apraxia only became apparent during tasks requiring certain coordinations between both arms or legs. Bimanual interaction was normal. Two patients with proximal hemiparesis and small lesions in the precentral gyrus which have been examined for comparison showed no limb-kinetic apraxia and different distributions of the paretic shoulder girdle muscles. In view of the long-standing controversies as to the functional role of the premotor cortex and the question of specific deficits after lesions of this area, the relevant literature is reviewed.

Adult↗

PubMed1984

Premotor cortex in man: evidence for innervation of proximal limb muscles.

Fourteen patients with frontal CT-lesions involving premotor cortex showed moderate weakness of contralateral shoulder and hip muscles. This premotor syndrome in man resembles that described for lesions of brainstem pathways in monkeys, except that axial musculature was not disturbed when these lesions were unilateral. Medial extent of the lesion involving the SMA was accompanied by additional slight limb-kinetic apraxia.

Cerebral Cortex↗

PubMedDate not supplied

Sensory input to the motor fields of the agranular frontal cortex: a comparison of the precentral, supplementary motor and premotor cortex.

Arm displacements applied to the passive, but awake monkey are powerful stimuli for activating neurones in somatotopically appropriate areas of the precentral cortex. We have found that neurones in medial area 6 (SMA) and in lateral area 6 (PMC) may likewise be activated by such kinesthetic stimuli, at latencies which are only slightly longer than in area 4. Confirming previous findings, PMC neurones were sometimes also responsive to visual stimuli. The 'somatosensory' cells in the SMA were found in the microexcitable zone of the more posterior part of the SMA from where motor effects were elicited in arm and trunk muscles. These sensory neurones tended to be clustered together and they were only exceptionally excited antidromically by peduncular stimulation. Thus, somatosensory signals have access to both the PMC and SMA suggesting that both areas may be implicated in sensory-guided or sensory-triggered movements.

Animals↗