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Biomedical subjects

M Wiesendanger

Publications and source records attributed to M Wiesendanger.

At least 91 records · Page 5Linked to original sources
PubMed1982

Structural and functional definition of the motor cortex in the monkey (Macaca fascicularis).

1. The details of the organization of the motor cortex and its anterior and posterior border were investigated in three monkeys by a combination of techniques including intracortical microstimulation (i.c.m.s.), electrophysiological recording of cutaneous and muscle afferent inputs to single cortical neurones, and electrophysiological and anatomical identification of corticospinal neurones; in addition, data from these methods were related to cortical cytoarchitecture.2. Almost 5000 individual cortical loci were tested with i.c.m.s. in the unanaesthetized monkeys. In this paper, we particularly consider the organization of the forelimb motor representation, and its relation to the representation of other parts of the body. I.c.m.s. thresholds of about 5 muA were common for evoking twitch movements and e.m.g. responses in distal forelimb and face, jaw and tongue muscles, but proximal forelimb, trunk and hind-limb movements also sometimes had such low thresholds.3. The fingers were found to be represented nearest the central sulcus, with horseshoe-shaped bands of cortical tissue representing progressively more proximal muscles situated around this central ;finger core'.4. Cytoarchitectonically, the cortex having these low-threshold motor effects was characteristic of area 4. There was also a close fit between the extent of this ;excitable cortex' and the extent of densely spaced corticospinal neurones identified electro-physiologically or with horseradish peroxidase labelling. In subsequent mapping of forelimb afferents to the cortex when the animal was deeply anaesthetized, low-threshold and short-latency responses to muscle nerve stimulation were rarely found in this ;excitable cortex'.5. The anterior border could be clearly established by i.c.m.s. and by the sharp boundary of corticospinal neurones. It was noted that the motor cortex extends rostrally beyond area 4 and its anterior border appears to reside in the posterior part of area 6aalpha (Vogt & Vogt, 1919) although it is difficult to establish the precise transition from area 4 to area 6.6. Posteriorly, the ;micro-excitable cortex' was found to be limited to regions cytoarchitectonically delineated as area 4 and did not include area 3a. On the other hand, low-threshold forelimb proprioceptive afferent inputs appeared restricted to area 3a neurones in the deeply anaesthetized animal. Corticospinal neurones were very dense in area 4, and there was a clear decrease in their occurrence in more caudal areas. However, scattered nests of corticospinal neurones were noted in areas 3a, 3b, 2, 1 and 5. It remains to be seen whether these scattered nests could be directly involved in motor control or whether they may modulate ascending somatosensory transmission, and whether they rely on sensory feed-back or inputs from other central areas for their spinal effects.

Animals↗
PubMed1981

The somatotopy of the gracile nucleus in cats with agenesis of a hindfoot.

The somatotropic representation of the hindlimb in the gracile nucleus was studied in two cats who had a congenital defect of one hindfoot. The defect comprised all of the foot downward from and including the heel, and the distal third of tibia and fibula. The part of the sciatic nerve normally supplying the lower hindlimb and the hindfoot was reduced in diameter by one third. The motoneurones corresponding to the absent muscles were lacking and replaced by glial elements. The cross-sectional area of the dorsal columns at segment S2 was reduced by more than 20%. The gracile nuclei, in contrast, were not reduced in size. Only the diameter of its neurones was significantly smaller. Electrophysiological single and multi-neurone recordings revealed an altered somatotopic representation in the gracile nucleus on the defective side. The nuclear area normally representing the missing parts of the body surface now received input from the stump. There was no nuclear area devoid of afferent input, and there was no input in the gracile from the forelimb or from the contralateral side. It is concluded that the remaining parts of the leg project onto the gracile nucleus in an ordered fashion, sharing the entire nucleus according to their present afferent fibres.

Afferent Pathways↗
PubMed1978

Spinal projection to the dorsolateral nucleus of the caudal basilar pons in the cat.

In the cat, a spinal projection to a restricted area of the basilar pontine grey has been revealed with use of anterograde degeneration technique (Fink-Heimer). The area was ipsilateral to the spinal lesion, restricted to the far caudal limit of the pons, and included the dorsal and the dorsolateral subdivisions of the pontine nuclei (PN). Comparisons following high cervical, midthoracic and upper lumbar spinal lesions did not reveal any somatotopic organization. Only a few spinopontine fibers had origins below segmental level L4. Lesions of various quadrants of the cord indicated that the spinopontine fibers ascended through the dorsolateral funiculus, and not through either the dorsal or the ventral funiculi. Comparison with the degeneration effects of cerebral cortical lesions showed that the spinal projection to the PN overlapped to some extent with the projection from the first sensorimotor and second somatosensory cortices. In the rat no comparable spinopontine projection was found. It is suggested that the spinopontine pathway might forward information to the cerebellum from visceral sensory receptors or perhaps from pools of spinal interneurons.

Animals↗
PubMed1976

Input from trigeminal cutaneous afferents to neurones of the inferior olive in rats.

Extracellular recordings were obtained from inferior olivary neurones of the rat. The responses of fifty neurones evoked by electrical stimulation of a branch of the trigeminal nerve were recorded. Maxillary nerve stimulation was most effective. The response was characterized by an early discharge (single spike and wave, typically with latencies between 16 and 30 msec) and a weak late discharge which followed a period of inhibition of about 100 msec. Half of the neurones responded to one branch of the trigeminal nerve only whereas the other neurons displayed a varying degree of convergence, including sometimes a convergence from limb nerves. Forty-nine olivary neurones were tested for cutaneous receptive fields. Ten out of these had small receptive fields (less than 20% of the contralateral face) and a low threshold to mechanical stimuli. Twenty neurones which had larger receptive fields responded also to low-threshold or to medium-threshold (i.e. non-nociceptive) mechanical stimuli. None of the neurones displayed receptive fields more extensive than half of the contralateral face and some of the larger fields had a small, low-threshold focus. Olivary neurones responding to electrical stimulation of trigeminal nerves or mechanical stimulation of the face were located in the medial segment of the olivary complex (dorsal accessory and principal olive). A few cells only were located in the lateral segment. It is concluded that neurones of the inferior olive receive a substantial input from trigeminal afferents and are capable of transmitting precise somatotopical information to the cerebellum.

Afferent Pathways↗
PubMed1975

Why transcortical reflexes?

Experiments in humans and in monkeys have indicated that load perturbations, occurring during voluntary movements and postural activity, may be automatically compensated for. Overall muscle stiffness opposing load changes is determined by the visco-elastic properties of the muscle, by segmental reflex actions and finally by long-loop reflexes. Under certain circumstances, for instance when the subject or the experimental monkey is "prepared" to counteract perturbations which are unpredictable in time, the long-loop "reflexes" appear to be responsible for most of the corrective muscle tension. Experiments in anaesthetized monkeys revealed that signals from stretch afferents reach neurons of the motor cortex, possibly via a relay in the cortical area 3a. The latencies of these responses to well controlled muscle stretches were in the same range as motor cortical cell discharges recorded in alert monkeys subjected to load perturbations. Furthermore, these responses of cells in the motor cortex also had the appropriate timing to indicate a causal relationship with the long-latency electromyographic responses to load changes referred to above. These experimental results therefore strongly support the hypothesis, first proposed by Phillips (1969), of a transcortical servo-loop adjusting motor cortical output according to the load conditions in which movements are performed. The major advantage of transcortical regulations as opposed to segmental regulations, seems to be a powerful gain control acting at the cortical level; it was repeatedly shown that the long-loop reflexes are strongly modifiable and under voluntary control. It is suggested that an adaptive gain control at the cortical level is a prerequisite to preserve the complex capabilities of the motor cortex as the chief "executive" for skilled, preprogrammed movements. A loss of this adaptive gain control may be, at least partly, the cause of motor disorders such as rigidity in Parkinsonian patients, as reported by Tatton and Lee (1975). It is suggested that further investigations of the control of transcortical reflexes may aid in the understanding of the pathophysiology of motor disabilities.

Animals↗
PubMed1975

Organization of climbing fibre projections to the cerebellar cortex from trigeminal cutaneous afferents and from the SI face area of the cerebral cortex in the cat.

1. In cats anaesthetized with pentobarbitone, the projection of climbing fibres (CFs) to the cerebellar cortex from trigeminal cutaneous branches and from the face area of the sensorimotor (SI) cortex was mapped, using the technique of laminar field potential analysis. 2. The CF projections from both the trigeminal nerve and the SI face area were found to be localized to the same cerebellar folia, viz. chiefly the ipsilateral lobule HVI, with a small overlap on to the adjacent folia of lobule V and crus Ia of HVIIA. Frequently a projection from the superficial radial nerve to part or all of this area, was also found. 3. A correspondence in the distribution and amplitudes of CF potentials evoked at most points by stimulation of the trigeminal nerve and the SI cortex was found. This implies a convergence of afferents from these two sources at or before the inferior olive. 4. In more than half of the cats, a small area of the cerebellar hemisphere was found, in which contralateral as well as ipsilateral trigeminal stimulation would evoke CF potentials. Usually inputs from the superficial radial nerve and the SI cortex also converged upon this area. 5. The organization of CF projections from trigeminal and superficial radial nerve afferents to the cerebellar hemisphere was found to occur in the same 'patchy' pattern of somatotopy that has been described for spinal nerve inputs to the anterior lobe. 6. One constant factor was found in the pattern of organization of CF projections to this area from cutaneous afferent nerves. That is, only the afferents from overlapping areas of skin projected to a given recording point: no instance of CF projections from trigeminal branches innervating discontinuous skin areas was observed.

Animals↗
PubMed1975

Climbing fibre inputs to cerebellar Purkinje cells from trigeminal cutaneous afferents and the SI face area of the cerebral cortex in the cat.

1. An investigation was made of climbing fibre (CF) activity evoked in single Purkinje cells in the cerebellum by electrical stimulation of trigeminal cutaneous afferents, the face area of the SI cortex, and the superficial radial nerve, in Nembutal-anaesthetized cats. In addition, both the extent of the cutaneous receptive fields of individual Purkinje cells on the face and the CF responses evoked in these cells by controlled natural stimulation were examined. 2. The pattern of convergence from these inputs on to individual Purkinje cells was found to be complex. DF responses were evoked in 67% of trigeminally-activated cells by electrical stimulation of more than one trigeminal branch. An excitatory CF convergence from the face area of the SI cortex was found on 68% of trigeminally activated cells; 23% also responded to stimulation of the superficial radial nerve. 3. In 81% of the Purkinje cells which were activated by trigeminal nerve stimulation, CF responses were readily elicited by gentle mechanical stimulation of the facial skin. A qualitative relationship was established between the size of the peripheral field of a Purkinje cell, and the probability of convergence on to that cell from the SI cortex. 4. Recordings were made from a limited number of Purkinje cells which were responsive to electrical stimulation of bilateral trigeminal branches and the superficial radial nerve. However, CF responses in these cells often could be elicited only by high intensity stimulation. It is suggested that these cells are analogous to, or perhaps an extension of the population of Purkinje cells described in the anterior lobe which are excited via the ventral funiculus pathway in the spinal cord only by stimulation of 'flexor reflex afferents' in bilateral limb nerves.

Animals↗
PubMed1975

Corticofugal effects from sensorimotor area I and somatosensory area II on neurones of the pontine nuclei in the cat.

1. The objective of the present experiments was to study the cortical influence from sensorimotor area I (SM I) and from somatosensory area II (S II) on single neurones of the pontine nuclei (PN) in cats under N2--thiamylal anaesthesia. 2. Extracellular single unit recordings revealed a considerable convergence from S II and SM I. Out of ninety-one PN neurones (identified as ponto-cerebellas neurones by antidromic stimulation of the contralateral brachium pontis), fifty-seven neurones were influenced by stimulation of at least one cortical site. Slightly less than half of these neurones (twenty-five) had a convergent input from SM I and S II; twenty-three PN neurones were excited by SM I only and nine PN neurones by S II only. The proportion of PN neurones excited via collaterals of cortico-spinal neurones was small and restricted to those neurones which had an input from SM I. 3. Sixty per cent of the ponto-cerebellar neurones were reliably activated by natural stimulation such as tapping or passive manipulations of limbs of various joints. The vast majority (thirty-three out of thirty-six PN neurones) which had receptive fields were also influenced by electrical stimulation of one or both cortical areas. The long latency and low probability of discharge to peripheral nerve stimulation suggest a complex, probably transcortical, pathway from the periphery to the PN. 4. The distribution of latencies to both cortical and brachium pontis stimulation indicates that the PN are a relay for fast and slow cerebro-cerebellar connexions. 5. The convergence from cortical areas on PN indicates that the neurones influenced from somatic areas SM I and S II transmit integrated patterns of activity to the cerebellum.

Animals↗
PubMed1975

Responses of neurones in motor cortex and in area 3A to controlled stretches of forelimb muscles in cebus monkeys.

1. The experiments were designed to investigate the effects of longitudinal muscle displacements on neurones of the motor cortex of anaesthetized Cebus monkeys and thus test the hypothesis that signals from muscle spindles may modify motor cortical output. The effects of sinusoidal stretching of the extensor digitorum communis (EDC) at frequencies varying from 6 to 300 Hz and of step and rhomboidal stretches were studied in neurones of the motor cortex. For comparison, neurones of the primary receiving area for low-threshold muscle afferents, cortical area 3a, were also included in this study. Neurones of the motor cortex were subdivided into corticospinal (PT) neurones and non-corticospinal (non-PT) neurones. 2. Threshold stretch amplitudes were clearly higher for neurones of area 4 (PT and non-PT) than for 3a neurones. However, a conspicuous fall in threshold stretch amplitude was observed for all three neurone populations when the frequency of sinusoidal stretching was increased (highest frequency: 300 Hz). A small number of non-PT and PT neurones responded to vibration amplitudes of less than 100 mum and some of these low-threshold cells of area 4 also responded to rhomboidal stretches of 8 mm/sec ramp velocity and 80 mum plateau amplitude. Increasing the stretch amplitude to twice threshold nearly doubled the output magnitude in all three cell types. Neurones of area 3a and non-PT neurones of area 4 had similar latencies, and these were significantly shorter than the latencies of PT neurones tested with trains of high frequency vibration. Dynamic response patterns were observed in all three cell types, but most frequently in 3a neurones. 3. It is concluded that, in Cebus monkeys, signals from both primary and secondary muscle spindle endings from forelimb muscles reach the motor cortex. Under the present experimental conditions, the input from the primaries to the motor cortex was effective only if these spindle receptors were driven maximally by vibratory stimuli. The particularly low probability of stretch-evoked discharges of cortico-spinal neurones in the anaesthetized preparation may be explained by a low gain in transmission from input to output cells of the motor cortex.

Animals↗