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Biomedical subjects

M Wiesendanger

Publications and source records attributed to M Wiesendanger.

At least 109 records · Page 6Linked to original sources
PubMed1974

Organization of corticofugal neurones in somatosensory area II of the cat.

1. This investigation had two main objectives: first to determine whether or not motor activity could be elicited by localized intracortical stimulation in somatosensory area II of the cat, and secondly to identify, by antidromic stimulation, neurones which projected to subcortical structures and to study their afferent input.2. Although arm movements could be elicited in most cats by intracortical train stimulation with tungsten micro-electrodes, the lowest motor thresholds were much higher than the lowest thresholds for the primary motor area under similar experimental conditions. Facial responses were evoked at lower stimulus thresholds, but the threshold decreased steadily as successive stimulation tracks approached the coronal face area. Previously observed responses to prolonged surface stimulation could have been caused by intracortical spread of excitation or by escape of stimulus to the primary area, especially the face area.3. Neurones with corticofugal axons projecting to bulbar and spinal levels were first identified by their antidromic response to stimulation of the cerebral peduncle. Each was further tested by stimulation of the cervical corticospinal tract, and the dorsal column nuclei. Their receptive fields were then recorded.4. It was possible to classify the neurones into four main categories: (i) non-descending neurones: neurones not activated antidromically by any of the subcortical stimulating electrodes. The majority of these neurones had very small (lemniscal type) receptive fields, (ii) corticobulbar neurones: these were invaded antidromically by stimulation of the peduncle but not by spinal or dorsal column nuclei stimulation. They had ;stocking-like' or larger receptive fields; (iii) cortico-spinal neurones: neurones driven antidromically by stimulation of corticospinal fibres. Characteristically, these neurones had large confluent fields, often bilateral. Very few had receptive fields of the lemniscal type; (iv) neurones invaded by dorsal column nuclei stimulation: the number of such units was extremely low and their receptive fields were large or ;stocking-like'.5. The results indicate that somatosensory area II in the cat does not exert an independent motor control of spinal neurones, and it is thought that corticofugal neurones of SII are involved in the control of somatosensory transmission rather than having a direct motor function.

Action Potentials↗
PubMed1973

Input from muscle and cutaneous nerves of the hand and forearm to neurones of the precentral gyrus of baboons and monkeys.

1. The precentral bank of the Rolandic fissure of the cortical arm area has been explored with extracellular micro-electrodes in primates (baboons and monkeys) under nitrous oxide and oxygen anaesthesia, supplemented by small doses of Parkesernyl(R) and chloralose. The results in baboons and monkeys were the same.2. Single units were classified as pyramidal tract neurones or non-pyramidal tract neurones according to their antidromic responsiveness to stimuli applied in the dorsolateral funiculus at C1-2.3. Responses to electrical stimulation of the deep (motor) radial nerve, the deep palmar (motor) branch of the ulnar nerve, and the superficial (cutaneous) radial nerve could be recorded in the majority of neurones of the motor cortex provided that short trains of strong stimuli were used. Minimal responses to muscle nerve stimulation were observed in a few neurones at 1.4 x group I threshold, but most units reacted only with higher stimulus intensities (2-3 x group I threshold).4. The latencies to peripheral nerve stimulation were measured from the first peak of the incoming volley recorded at the root entry zone. The mean response latencies of pyramidal tract cells were between 20 and 25 msec; non-pyramidal tract cells were activated at slightly shorter mean latencies, the difference being significant for superficial radial nerve stimulation only (4 msec). These latencies are more than twice as long as those recorded in the postcentral gyrus, and the probability of discharge is lower than for postcentral neurones.5. A further difference between neurones of the postcentral and precentral gyrus is the pronounced convergence from different nerves and also from different modalities (cutaneous and muscle afferents) in units of the precentral cortex in contrast to units of the postcentral cortex.6. The high thresholds, necessary to activate precentral neurones by muscle nerve stimulation, make it unlikely that group I muscle afferents are involved. This is, furthermore, indicated by the lack of responsiveness to intravenous injection of succinylcholine which was, however, effective for driving neurones of the specific projection area for group I afferents, area 3a. The present experiments are consistent with the view that sensitivity of precentral neurones to muscle stretch (described in previous studies) is due to activation of secondary muscle spindle endings and their ascending pathways.7. The original hypothesis of a load compensating ;pyramidal reflex' with an oligosynaptic afferent contribution from the spindle primaries can be discarded. The present findings indicate that there is a feed-back from secondary muscle spindle afferents which, by way of a more complex pathway, can modulate the firing frequency of neurones in the motor cortex.

Animals↗
PubMed1971

Projection from low-threshold muscle afferents of hand and forearm to area 3a of baboon's cortex.

1. The precentral and postcentral banks of the Rolandic fissure of the arm area of the baboon's cortex have been probed to their depths with extracellular micro-electrodes under nitrous oxide and oxygen anaesthesia, supplemented by minimal intravenous pentobarbitone or chloralose.2. Afferent volleys were sent in from the deep (motor) radial nerve and the deep palmar (motor) branch of the ulnar nerve. Their entry into the central nervous system was timed at the dorsal root entry zone. The nerves were stimulated in continuity and the effects of stimuli below threshold for the motor axons were investigated.3. Area 3a, in the depths of the postcentral bank, which is cytoarchitectonically transitional between areas 3 and 4, is the receiving area for afferent impulses from muscle.4. Evoked potential waves and unitary discharges began 4 msec, and the majority of units discharged between 5 and 10 msec, after the afferent volley reached the dorsal root entry zone.5. Similar responses were elicited by a brief pull (70 mu in 1 msec) or brief vibration (50 mu at 250-400 Hz) applied to the tendons of m. extensor digitorum communis.6. No potential waves were evoked in area 4, even in the depths adjacent to area 3a, by muscle afferent volleys.

Animals↗