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R Porter

Publications and source records attributed to R Porter.

At least 181 records · Page 10Linked to original sources
PubMed1980

The discharges during movement of cells in the ventrolateral thalamus of the conscious monkey.

1. Monkeys were trained to perform a stereotyped movement task in return for food rewards. On completion of training a headpiece which allowed microelectrode access to the thalamus for single cell recordings during performances of the task was attached at a surgical operation. The location of each cell studied was determined by histological examination of the fixed brain and precise identification of electrode tracks. 2. Ninety-three of ninety-seven cells discharging in association with arm movements but not responding to natural activation of peripheral receptors in the forelimb were located predominantly in the rostral part of nucleus VPLo and the caudo-ventral part of VLo. These cells appeared to be associated with active movement in one direction of a specific joint. 3. 52% of these 'motor' cells discharged in association with movements of either forelimb. The other 48% discharged in association with movement of the contralateral arm and hand only. 4. Sixty cells responded to stimulation of deep receptors or to passive limb manipulation in the relaxed and cooperative animal. These cells were predominantly located in the ventro-caudal part of VPLo and all the responses were obtained from contralateral receptors. Their discharges during performances of the motor task were indistinguishable from those of 'motor' cells. 5. Ninety-two cells were driven by limb manipulation and by natural activation of superficial cutaneous receptors and these were found predominantly in VPLo and VPLc. All responses were from contralateral receptors. These cells discharged during performance of the motor task; for some of them, their afferent input zones were not being stimulated by contact with the manipulandum when their 'motor' discharges commenced. 6. Although responses in each of the above groups of cells were sought by imposing a sudden perturbation of the limb during the performance of the active movement task, no responses were seen.

Action Potentials↗
PubMed1979

Discharges of intracerebellar nuclear cells in monkeys.

1. Conscious monkeys were trained with food rewards to perform movement tasks with the left forelimb and to accept manipulation of the joints and muscles and natural non-noxious stimulation of the skin of all four limbs. 2. Recordings were made from 217 cells situated in the left interpositus and dentate nuclei of the cerebellum. The identity of seventy-seven cells as cerebellar projection neurones was definitively established by activating them antidromically from the brachium conjunctivum near the contralateral red nucleus. 3. Modulation in the natural activity of 129 of these crebellar nuclear cells (sixty in interpositus; sixty-nine in dentate) occurred in a reproducible manner in temporal association with a phase of the self-paced movement tasks performed by the animal using the ipsilateral arm and hand. The discharges during motor performance of forty-two dentate and forty-five interpositus cells were shown to be associated with movement about a particular joint or region of the forelimb whenever that movement occurred. 4. Cells whose discharges were related to proximal joint movements (shoulder, elbow) and cells related to distal joint movements (wrist, fingers) were encountered in both the dentate and interposed nuclei. 5. The cells were tonically active at rest. Most commonly, accelerations in the discharge were related to movement of a joint or the limb in one direction and a reduction or cessation of activity accompanied movement in the opposite direction. 6. For some cells, variation of the amount of discharge demonstrated during movement performance could be related to the range of the movement or its duration, more activity being characteristic of more prolonged movement performance through larger angles of joint displacement. 7. The dentate and interpositus cells whose discharges were most strongly and consistently related to movements of the forelimb were concentrated in the mid region and caudal half of either nucleus. 8. None of seventy-three dentate neurones examined showed appreciable responses to stimulation of the skin or manipulation of joints and muscles of the fore- or hind limbs and only two cells responded to unexpected perturbation of movement performance. 9. No influence resulting from peripheral afferent input from the ipsilateral forelimb was detected in any interpositus cell whose firing was unchanged during ipsilateral arm movements. 10. Of the sixty interpositus cells whose discharge rates changed during motor performance, twenty-eight were demonstrated to be in receipt of input from receptors in the ipsilateral hand or arm, which could be activated by brisk tapping of the skin and sometimes by gentle squeezing of the forearm. 11. In the passive relaxed animal, manipulation of joints was ineffective in modifying the discharges of most interpositus neurones and, in all cases, prolonged pressure upon the skin elicited only transient responses...

Action Potentials↗
PubMed1979

Supplementary motor area in the monkey: activity of neurons during performance of a learned motor task.

1. Recordings were made of the natural discharges of neurons in the supplementary motor area (SMA) of conscious monkeys trained to perform stereotyped motor task, pulling a horizontal lever, with either hand. 2. Of the total population of cells, 80% showed modulation of their activity during particular movements of either limb. Many cells had a similar pattern of modulation regardless of whether the contralateral or ipsilateral hand was used. Of the remaining 20%, some cells were related to leg or body movements or to visual experience. 3. Cells whose activity was related to movements of distal joints were found in approximately equal numbers to those whose discharges occurred with proximal movements. 4. Only 5% of cells tested sent their axons into the pyramidal tract, and only 14% of units investigated showed responses to passive manipulation of the limbs. The effective afferent input usually was of a rather complex kind. 5. The findings suggest that the discharges of a large number of neurons in SMA are changing during particular movements of either arm, and that only a small number of cells receive peripheral afferent sensory input. These results contrast with those obtained in the primary motor area and suggest a different role for SMA in the control of movement.

Animals↗
PubMed1979

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History, Modern 1601-↗
PubMed1978

Deficient influence of peripheral stimuli on precentral neurones in monkeys with dorsal column lesions.

1. Four male monkeys (M. fascicularis) were trained in a movement performance task which involved pulling a horizontal lever into a target zone and then collecting, from one of a variety of positions, a small food reward. The same animals were also trained to sit quietly and accept passive manipulation and natural stimulation of the arm and hand while remaining relaxed. 2. After complete bilateral section of the cuneate fasciculi or division of a major part of these dorsal column afferents at C1-C2 or at C5 level, the animals were still able to perform movement tasks normally. Disturbance of discrimination ability was revealed after vision was occluded it the animal was required to detect differences in texture with only a small cutaneous area in contact with the object (e.g. using only the tip of the index finger). Contactual-placing reactions could be performed in the absence of vision and the movements the animal made in these reactions were well controlled and appropriately directed. Minimal disturbance of contact placing was noticed if the surface touched was on the hand or fingers or if the reaction involved crossed placing. 3. An examination of the natural discharges of 342 percentral neurones revealed that the patterns of activity exhibited in relation to complex movements were indistinguishable from patterns recorded in normal monkeys carrying out similar tasks. 4. Discharges of ninety-one of 321 precentral neurones could be produced by appropriate natural stimuli delivered within the cell's afferent input zone at the periphery. The zone from which a given cell could be influenced was usually limited and its location could be on any part of the contralateral forelimb. However, all but nine of these responses were found in animals in which a small proportion of the cuneate fibres remained intact. In an animal with histologically proven complete section of the cuneate faciculi very few (nine of 171) precentral neurones were influenced by natural activation of peripheral receptors in the forelimb. The zones from which these few afferent inputs were found could all have been proximal to the level of the cuneate lesion. 5. The very small number of responding pre-central neurones found in an animal with complete section of the cuneate fasciculi made it likely that the dorsal columns provide the major pathway for effects from circumscribed peripheral receptors in the forelimb to influence precentral neurones. However, even in an animal with complete interruption of cuneate fibres, a proportion of post-central neurones could still be influenced by natural activation of peripheral receptors within restricted regions of the forelimb. Hence the 'sensory' cortex was still in receipt of afferent projections which could be revealted readily by the tests used. 6...

Action Potentials↗
PubMed1978

Supplementary motor area of the monkey: activity of neurones during performance of a learned motor task.

1. Recordings were made of the natural dischages of neurones in the supplementary motor area (SMA) of conscious monkeys trained to perform a stereotyped motor task with either hand. 2. Eighty % of the total population of cells showed modulation of their activity during particular movements of either limb. Two thirds of this group had a similar pattern of modulation regardless of whether the contralateral or ipsilateral hand was used. 3. The number of cells whose activity was related to movements of distal joints was approximately equal to that whose discharges occurred with proximal movements. 4. Only 5% of cells tested sent their axons into the pyramidal tract, and only 15% of units investigated showed responses to passive manipulation of the limbs. The effective afferent input usually was of a rather complex kind. 5. The findings suggest that the discharges of a large number of neurones in SMA are changing during particular movements of either arm, and that only a small number of cells receive afferent sensory input. These results contrast with those obtained in the primary motor area and suggest a different role for SMA the control of movement.

Action Potentials↗
PubMed1977

Cells of origin and terminal distribution of corticostriatal fibers arising in the sensory-motor cortex of monkeys.

The cells of origin of the corticostriatal projection have been identified in squirrel monkeys by the use of the retrograde horseradish peroxidase method. In the subfields of the somatic sensory, motor, parietal and frontal areas of the cortex, cells projecting to the ipsilateral striatum are relatively sparsely distributed and form a group of small- to medium-sized pyramidal cells with an average somal diameter from area to area of 14-16 mum. Such cells are found only in layer V of the cortex (mainly in the more superficial parts of the layer). Since they are consistently smaller than the pyramidal cells of layer V that project to the brainstem and spinal cord and since they lie outside layer VI which gives rise to corticothalamic axons, the corticostriatal axons are unlikely to be collaterals of axons projecting to other sites. The cells of origin of the crossed corticostriatal projection are also found in layer V and are pyramidal cells with somal diameters in the same range as above. They are found only in areas 4, 8, and 6. Studies with the anterograde, autoradiographic method in rhesus, cynomologous and squirrel monkeys, indicate that the somatic sensory areas project to most of the antero-posterior extent of the ipsilateral putamen. Subareas 3a, 3b, 1 and 2 of the somatic sensory cortex project to the same region and the projection overlaps similarly extensive projections from the motor and certain other areas of the cortex. However, in each case the pattern of terminal labeling is in the form of interrupted clusters, strips and bands. A single small injection of the cortex is associated with only one or two such clusters of terminal labeling. This seems to imply that individual corticostriatal fibers end in a very restricted manner and that the terminal ramifications of fibers from one cortical area may alternate in the putamen with those arising in other areas.

Animals↗
PubMed1977

Management factors and grass tetany in dairy cattle.

The relationship between intensity of production and the occurrence of hypomagnesaemia and grass tetany in dairy cattle was investigated from 1966-1970 at the Ellinbank Dairy Research Station, Warragul, Victoria. Hypomagnesaemia and/or grass tetany occurred in cows grazing at both high (3.2 cows/hectare) and low (2.2 cows/hectare) stocking rates over the four-year period. Pasture Mg concentrations remained relatively high (0.2% dry matter) throughout this period, except in the low stocking rate pastures in one year, 1967. It is concluded that hypomagnesaemia and grass tetany was precipitated by a combination of low dry matter intake in winter and the effects of a gradual increase of K concentration in autumn and winter pastures, following the heavy application of K fertilizer. Under these conditions, MgO supplementation was inadequate to prevent grass tetany occurring in some animals.

Animal Husbandry↗
PubMed1977

The natural discharges of Purkinje cells in paravermal regions of lobules V and VI of the monkey's cerebellum.

1. Conscious monkeys were trained with food rewards to perform movement tasks with the left hand and to accept manipulation of the joints and muscles and natural non-noxious stimulation of the skin of both forelimbs.2. Recordings were made from 230 Purkinje cells situated in the paravermal region of lobules V and VI or immediately adjacent folia of the left cerebellum in a region from 2 to 7 mm from the mid line. These neurones were all in a zone which was demonstrated to receive inputs from the ipsilateral hand and which is known to receive projections, via the pontine nuclei from the ;arm area' of motor cortex in the right hemisphere.3. Modulation of the natural activity of 182 of these 230 Purkinje cells (79%) occurred in a reproducible manner in temporal association, each with a particular phase of the self-paced movement tasks performed by the animal using the ipsilateral arm and hand. The patterns of modulation of Purkinje cell firing in this limited zone of cerebellar cortex could be classified into one of four groups, and each cell's discharge was associated with a particular aspect of movement such as general arm flexion, shoulder retraction, elbow extension or elbow flexion whenever it occurred.4. The cells were spontaneously active at rest. Most commonly, marked accelerations of the discharge were related to one direction of the particular aspect of movement and a reduction of activity or even total silence accompanied movement in the opposite direction.5. Variation of the amount of discharge demonstrated during a movement performance with which this discharge was characteristically associated could be related to the range of the movement or its duration, more activity being characteristic of more prolonged movement performance through larger angles of joint displacement.6. Both simple spikes and complex spikes of some cells showed characteristic modulation of their activity during the monkey's self-initiated movements. Cells whose simple spikes did not change in frequency during the movement task, also showed no modification of complex spike discharge.7. Of the 182 neurones whose discharges changed during active movement performance, 105 (roughly 60%) were demonstrated to be in receipt of an input from peripheral receptors in the hand which could be activated by brisk tapping of the skin or brushing of hairs. In contrast, none of the Purkinje cells whose discharges were unchanged during arm movements could be demonstrated to receive such an input.8. Movement of joints through their full range and prodding of muscles were completely ineffective stimuli for causing changes in Purkinje cell firing in this zone of the cerebellar cortex while the animal was passive and relaxed. Imposed perturbations of movement performance injected unexpectedly during the execution of a movement task were also ineffective in modifying the discharge of these Purkinje cells in relation to the task.

Action Potentials↗
PubMed1976

Timing of the responses in the motor cortex of monkeys to an unexpected disturbance of finger position.

Monkeys were trained with food rewards to hold the wrist and fingers of their right hand in a flexed posture and maintain force with the finger tips against an isometric lever for a number of seconds. Once the animal had learned to produce a reliable performance of the task an assembly was attached to the skull through which microelectrodes could be introduced into the precentral cortex to record the activity of single neurones. Neurones whose activity was correlated with the force of finger flexion were studied; some of these could be identified as pyramidal tract neurones by their response to electrical stimulation in the medullary pyramids. While the monkey was flexing against it, the lever was sometimes suddenly released so that the fingers flexed without resistance. This unexpected disturbance was often followed by a change in the discharge of precentral neurones, although the monkey had not been trained to respond to the release in any particular way. On release of the lever the discharge of a given cortical neurone might either increase or decrease, and the direction of this change could not be predicted from the behaviour of the neurone during the isometric task. The most common response was an increase in cortical cell firing in neurones whose natural discharge was associated with the active development of force. The discharge of pyramidal tract neurones changed 25-50 msec after the sudden unexpected peripheral disturbance. Earlier changes were seen in some other neurones situated within the precentral gyrus and in the anterior bank of the central sulcus.

Animals↗