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Biomedical subjects

R N Lemon

Publications and source records attributed to R N Lemon.

At least 91 records · Page 5Linked to original sources
PubMed1981

Divergent collaterals from deep cerebellar neurons to thalamus and tectum, and to medulla oblongata and spinal cord: retrograde fluorescent and electrophysiological studies.

In cat the existence of collaterals from deep cerebellar neurons, which project to mesencephalon and thalamus has been investigated anatomically by means of the multiple retrograde fluorescent tracer technique as well as electrophysiologically by means of conventional antidromic techniques. Both sets of data indicate that several neurons in the medial nucleus, which project to mesencephalon and thalamus, also distribute collaterals to medulla oblongata and spinal cord. These branching neurons were principally located in the caudal and intermediate portions of the medial nucleus. The electrophysiological data in addition indicate that the branching point of the neurons in the medial nucleus is located relatively close to the cell soma. The anatomical findings show a further group of branching neurons in the lateral nucleus at the border with the interpositus nuclei. The majority of these latter neurons distribute collaterals to medulla oblongata but some distribute collaterals to spinal cord. However, it could not be decided as yet whether the collaterals to the medulla oblongata terminate either in medullary medial reticular formation or in inferior olive or in both.

Animals↗
PubMed1981

Behaviour of neurons in monkey peri-arcuate and precentral cortex before and during visually guided arm and hand movements.

Neuron activity was recorded in monkey cerebral cortex during a visually guided reaching task. Cells located in the banks of the arcuate sulcus at its curvature changed their activity during the period in which the monkey saw a food reward in a certain position, but before it moved to retrieve the reward. A role of these neurons in visual guidance of arm and hand movements is postulated.

Animals↗
PubMed1981

Functional properties of monkey motor cortex neurones receiving afferent input from the hand and fingers.

1. Records have been made from area 4 of the cerebral cortex in five conscious monkeys. The properties of 216 neurones responsive to natural stimulation of the hand and fingers have been investigated.2. 46% of these neurones responded only to cutaneous stimulation (especially light brushing across the glabrous skin) and a further 38% responded only to movement of the digits. 4% responded to brief prods of the hand. 12% of the sample responded to more than one stimulus modality.3. Many hand-input neurones, including pyramidal tract neurones, responded at short-latency (8-15 msec) to light mechanical stimulation of the hand and to weak electrical stimulation of the median nerve.4. Responsive neurones were found at all depths of the cortical grey matter. Responses of shortest latency were encountered in neurones probably located in layers IV and V.5. The behaviour of eighty hand-input neurones was analysed during a simple, stereotyped task which involved pulling a lever and collecting a food reward from a small well. For comparison, the activity of 117 neurones with inputs from the wrist, elbow or shoulder was also analysed.6. Nearly all hand-input neurones modulated their activity either before (48/80) or during (29/80) the retrieval of the reward which required precision grip between index finger and thumb. Many were silent during proximal arm movements and some displayed activity patterns independent of these movements.7. By contrast, the activity of many neurones with proximal arm (elbow, shoulder) inputs was unrelated to food retrieval and manipulation, but well related to arm movements.8. Forty-three of the eighty neurones had cutaneous input from the hand. Twenty-seven were active before hand contact. Thirty-five modulated their discharge when contact was made (twenty-one excitation, fourteen inhibition).9. Most hand-input neurones were more active during fractionated movements of the hand or fingers than during power or ball grips requiring simultaneous flexion of all digits. Neurones with glabrous inputs often showed intense activity during small, precise finger movements and during active tactile exploration without the aid of vision.10. Analysis of the discharge frequency of twenty-five hand-input neurones revealed that some (mainly non-pyramidal tract neurones) had a similar mean frequency and range of modulation during both active movement and passive stimulation. Others (mainly pyramidal tract neurones) had a greater frequency range and higher mean frequency during active than during passive movements.

Action Potentials↗
PubMed1981

Variety of functional organization within the monkey motor cortex.

1. Single-unit recordings have been made from 606 neurones in the arm region of area 4 in five conscious monkeys. Their activity during a stereotyped motor task and their responses to passive natural stimulation of the limb have been investigated.2. 88% of area 4 neurones responsive to natural stimulation received their afferent input from a restricted region of the contralateral arm.3. The activity and afferent input to cell groups have been determined by comparing the properties of neurones located within 500 mum of each other and recorded in one and the same micro-electrode penetration. 115 such cell groups containing 344 neurones were investigated.4. 75/115 cell groups (65%) contained neurones with input from the same arm zone (shoulder, elbow, wrist or hand) and with a similar pattern of task-related activity. Cell groups containing neurones with identical afferent inputs never showed contrasting behaviour during movement.5. 40/115 cell groups (35%) contained neurones receiving inputs from more than one arm zone. Twenty-five cell groups (22%) had two contiguous zones (e.g. wrist and hand) represented and ten groups had input from two discontinuous zones (e.g. elbow and hand). These differences in input within a cell group were usually reflected in contrasting behaviour of its constituent neurones during movement.6. Pyramidal tract neurones (PTNs) lying immediately adjacent to one another usually received similar inputs and exhibited matching behaviour. PTNs lying further apart in the same penetration often showed different activity and responded to different stimuli.7. The topographic distribution of afferent input to area 4 revealed multiple representation of input from a single zone combined with considerable intermingling of input from all four zones. Neurones with shoulder and elbow inputs surrounded those with wrist inputs which in turn lay scattered around a central zone. This central zone only contained neurones with hand inputs, although neurones with hand inputs were found outside this central zone.8. The significance of this complex organization is discussed in terms of motor cortex input and output.

Afferent Pathways↗
PubMed1980

Absence of callosal collaterals derived from rat corticospinal neurons. A study using fluorescent retrograde tracing and electrophysiological techniques.

In rat the presence of axon collaterals from corticospinal neurons to the contralateral hemisphere has been investigated by means of anatomical and electrophysiological techniques. Anatomical Experiments. Several combinations of fluorescent retrograde tracers were used. In eight rats injections of Evans Blue, "True Blue", "Fast Blue" or DAPI-Primuline were made in areas 10, 6, and 4 and in the most medial part of the S1 granular cortex of one hemisphere, 1.5 mm below cortical surface. These injections were combined with injections of "Fast Blue", DAPI-Primuline, "Granular Blue", "Nuclear Yellow", or Bisbenzimide in the ipsilateral corticospinal tract in the C2 segment. Survival times of the animals varied according to the tracers used. In the non-injected hemisphere the retrogradely labeled corticospinal neurons were present in layer V of especially areas 10, 6, 4 and the medial portion of the S1 granular cortex. However, the retrogradely labeled callosal neurons in these areas were present in all layers except layer I. The labeled callosal and corticospinal neurons in layer V were intermingled and frequently situated very close to one another. However, with none of the tracer combinations were double labeled neurons observed. Electrophysioloogical Experiments. In six rats, layer V neurons of hindlimb-sensorimotor cortex were tested for antidromic responses to stimulation of contralateral corticospinal tract (CST) and corpus callosum (CC). Eighty-five CST neurons were identified, none of which responded antidromically to CC shocks. Eighty-two layer V neurons were identified which responded antidromically to CC shocks, but none of them responded antidromically to CST shocks. CC shocks elicited strong synaptic responses in CST neurons and vice versa. Depth measures indicated extensive intermingling of CST and CC neurons. From both sets of findings it was concluded that, in rat, CST neurons do not give rise to callosal collaterals.

Animals↗
PubMed1979

Short-latency peripheral inputs to thalamic neurones projecting to the motor cortex in the monkey.

One hundred seventy-five neurones in the n.ventroposterior lateralis (VPL) and n.ventralis lateralis (VL) in the thalamus of anaesthetised monkeys have been tested antidromically for projection to the cortex and for somatosensory input from the contralateral arm. Using bipolar stimulation of the cortical surface, 113 thalamic neurones were successfully identified as antidromically driven from the hand area of the postcentral gyrus (48 neurones) or from the hand area of the precentral gyrus (65 neurones). All but one of these 113 neurones could only be antidromically discharged from the postcentral cortex or from the precentral cortex, and not from both. Most had antidromic latencies between 0.5 and 1.5 ms. Twenty-five/sixty-five precentrally projecting neurones and 45/48 postcentrally projecting neurones were activated by stimulation of the contralateral median or radial nerves. Both groups responded at short latency (4--8 ms) and many were activated by low-threshold shocks (0.8--1.3 T) and had restricted receptive fields on the hand. Precentrally projecting neurones responded most powerfully to joint movement or deep pressure, and some of these neurones were also responsive to cutaneous stimuli. Precentrally projecting neurones with peripheral inputs were all found in the oral subdivision of the VPL (the VPLO). The properties of these neurones suggest that they may be partly responsible for rapid somatosensory input to the motor cortex.

Afferent Pathways↗
PubMed1979

Cells of origin of the frontal projections to magnocellular and parvocellular red nucleus and superior colliculus in cynomolgus monkey. An HRP study.

Cells of origin of frontal cortical projections to parvocellular and magnocellular red nucleus (MRN) and superior colliculus were identified by means of retrograde HRP transport. The cells projecting to parvocellular red nucleus (PRN) are mainly located in areas 6 and 4, and are situated in the upper part of layer V, i.e. above the Betz cells, while those projecting to MRN are mainly located posteriorly in area 4, and are situated deep in layer V, i.e. at the level of the Betz cells. The neurons projecting to superior colliculus are located deep in layer V of areas 9, 8 and 6.

Animals↗
PubMed1975

Sensorimotor cortical representation in the rat and the role of the cortex in the production of sensory myoclonic jerks.

1. After administration of 1,2-dihydroxybenzene (catechol) to anaesthetized rats, rabbits and cats, a reflex jerk consisting of three distinct components was evoked in the limb muscles by peripheral stimulation. The second component of the jerk in the forelimb muscles of all three animals was specifically abolished by lesions confined to the contralateral forelimb sensorimotor cortex. 2. These lesions had no effect on the second response in either the hind limbs or in the forelimb ipsilateral to the lesion. The first and third responses were also unaffected. 3. Lesions in the cat hind-limb cortex abolished the contralateral hind-limb second response, but not the ipsilateral hind-limb or forelimb response. 4. In the rat and rabbit, unilateral hind-limb sensorimotor lesions were ineffective in completely abolishing the second response in the contralateral hind-leg muscles, and in addition, reduced the probability of occurrence of the response in the ipsilateral hind leg. Bilateral lesions abolished the response. 5. Re-investigation of the sensory and motor representation of the hind limb in the rat cortex revealed that this is bilateral in nature. Short-latency cortical responses (ca. 7-0 msec) could be evoked in one cortex by stimulation of either hind paw. The geometric centre of the cortical area from which these responses could be recorded was identical for each hind paw. 6. After catechol injection, stimulation of the cortical surface with single anodal shocks of threshold strength produced responses at similar latency (ca. 8-0 msec) in both hind limbs. 7. The behaviour of the second response after cortical lesions corresponds closely with the pattern of the somatosensorimotor cortical representation. The latency of the response is such as to allow its production by a long-loop cortical reflex, and this possibility is discussed.

Animals↗