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J Hore

Publications and source records attributed to J Hore.

51 records · Page 3Linked to original sources
PubMed1981

Characteristics of saccadic dysmetria in monkeys during reversible lesions of medial cerebellar nuclei.

1. The accuracy of saccadic eye movements made by trained Cebus monkeys was studied during reversible lesions produced by cooling through probes implanted between the interpositus and fastigial nuclei (medial probe) or lateral to the dentate nucleus (lateral probe). 2. Cooling through the lateral probe did not impair the accuracy of vertical or horizontal saccades, However, cooling through the medial probe produced a dysmetria whose magnitude was dependent on the position of the eye and on the direction of the saccade. 3. The amplitude/duration relation of dysmetria saccades was not significantly different from that of normal saccades. 4. The trajectories of the horizontal and vertical components of oblique saccades remained essentially straight during medial probe cooling in spite of unequal dysmetria in the two components. This suggests that the mechanism that produces a dysmetria in one component must interact with the gaze center that determines the duration of the other component. 5. Cerebellar nuclear cooling through either lateral of medial probes did not alter the saccadic reaction time to a randomly timed step change in target position. This result differs from that found for limb movements where cerebellar dysmetria was associated with increased reaction times. 6. These results provide evidence that the cerebellum through the medial nuclei normally plays a role in terminating, but not in initiating, saccades.

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PubMed1980

Arm movement performance during reversible basal ganglia lesions in the monkey.

Arm motor performance of eight Cebus monkeys was examined during reversible cooling in the ventral lateral region of the putamen and globus pallidus (primarily the external segment), where neurons discharging during arm movements have been found (DeLong 1972). When attempting to hold a handle stationary during basal ganglia cooling, all monkeys developed flexion at the wrist and some developed a slow flexion drift of the arm at the elbow. The prominence of wrist flexion emphasizes that the basal ganglia may normally influence distal musculature. During basal ganglia cooling an increase in segmental stretch reflexes (15-30 ms) was sometimes observed following arm perturbations, but no consistent increase occurred in the later EMG responses (30-95 ms) in contrast to results obtained in Parkinsonian patients (Tatton and Lee 1975). No major changes were observed in the time of onset of the earliest EMG activity in the agonist muscle in a simple reaction time elbow movement task during basal ganglia cooling. Basal ganglia lesions produced major disorders in both flexion and extension movements including slowing of movements and rebound of the arm towards its initial position after onset of movement. These disorders were accompanied by an increase in tonic activity of both flexors and extensors while holding and by increased levels of cocontraction of agonists and antagonists during attempted movements. It is suggested that this basal ganglia disorder is due to a failure to achieve the correct balance of activity between agonists and antagonists that is appropriate for a particular motor act.

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PubMed1977

Basal ganglia cooling disables learned arm movements of monkeys in the absence of visual guidance.

Unilateral local cooling in the region of the globus pallidus of Cebus monkeys produced a severe breakdown in the performance of learned flexion-extension elbow movements when animals had no visual information about arm position but not when such information was displayed to them. This result indicates that visual information enables an animal to compensate to a large degree for the motor disorder produced by globus pallidus dysfunction, and it may explain why some previous workers have failed to see motor impairments in monkeys with lesions in the globus pallidus who were observed in their cages.

Action Potentials↗
PubMed1976

Inputs from low threshold muscle and cutaneous afferents of hand and forearm to areas 3a and 3b of baboon's cerebral cortex.

The posterior wall of the central sulcus in forelimb area of SI has been expolred with extracellular micro-electrodes in baboons lightyl anaesthetized with nitrous oxide and sodium thiopentone. 2. The excitatory responses of 130 single units to low intensity electrical stimulation of the deep radial (muscle) and the superficial radial (cutaneous) nerves have been investigated. 3. Units that responded only to muscle nerve stimulation were located in area 3a but overlapped into area 3b. Units that responded only to cutaneous nerve stimulation were found mainly in area 3b but a number occurred in area 3a. Units that responded to both muscle and nerve stimuli (convergent units) were found throughout area 3a and the rostral part of area 3b. 4. Latency analyses of all three response groups revealed a single population of units responding to low threshold muscle nerve stimulation (mean latency 8.5 msec), and both early and late populations responding to low threshold cutaneous nerve stimulation (mean latencies 9.5 and 13.6 msec respectively). A number of the convergent units had very similar latencies for both inputs. 5. Electrical stimulation within area 3a deminstrated a projection from areas 1 and 3b to area 3a; such a pathway may provide a route for excitation of the late skin population which was found mainly in area 3a. 6. In area 3a units commonly responded to light touch, local pressure or deep pressure but only rarely to movement of hairs. A number of the convergent units responded to natural stimulation of cutaneous receptors.

Action Potentials↗
PubMed1976

Responses of cortical neurons (areas 3a and 4) to ramp stretch of hindlimb muscles in the baboon.

1. A study was made of the response of single cortical units in areas 3a and 4 to electrical stimulation of hindlimb muscle nerves and to ramp stretch of hindlimb muscles in baboons anesthetized with chloralose.2. Stimulation of hindlimb muscle nerves revealed a group I projection primarily to area 3a but with some input into adjacent area. 4. A major group II projection was found in area 4 adjacent to area 3a. A small number of area 3a neurons receive convergence from both group I and group II muscle afferents.3a. On the basis of their response pattern to ramp stretch, units were classified into one of six categories and their cytoarchitectonic location was determined. Units in area 3a had hynamic sensitivities equivalent to that of the primary spindle afferents. Although the discharge of some area 3a neurons also reflected differences in muscle length, most area 3a neurons had low position sensitivities. One unit type in area 3a did not respond to maintained muscle stretch and signaled only velocity of stretch.4. Units in area 4 had position sensitivities equivalent to that of primary and secondary spindle afferents. Although the discharge of some area 4 units reflected different velocities of muscle stretch, these units had dynamic sensitivities similar to those of secondary spindle afferents rather than those of primary afferents. One type of unit in area 4 had no dynamic component to muscle stretch and signaled only muscle length.5. The results demonstrate that there is a transfer of dynamic and position sensitivity from spindle afferents to cortical neurons. Furthermore, data processing has occurred because some units respond only to the steady-state length of muscle, while other units encode only the dynamic phase of stretch. This behavior is different from the responses to ramp stretch of either group I or group II muscle afferents in the baboon.6. The results demonstrate that single units in cerebral cortex can encode the information transmitted to the central nervous system by muscle spindle afferents. The purpose for which this information is used remains undetermined.

Action Potentials↗
PubMedDate not supplied

Characteristics of nystagmus produced by reversible lesions of the medial cerebellar nuclei in the alert monkey.

Synaptic activity of the medial cerebellar nuclei was reversibly blocked in 6 Cebus monkeys by cooling through a sheath implanted alongside the fastigial nucleus. Such lesions produced in the dark a strong nystagmus (slow phase velocity 100-200 deg/sec). The slow phase of nystagmus was predominantly in the horizontal plane and was towards the side of the lesion (ipsilateral drift). The maximum velocity of drift was independent of eye position and was directly related to the degree of cooling. Vision abolished the nystagmus. If lights were turned on during nystagmus the drift velocity rapidly decreased to zero with an instantaneous and an exponential component. It is suggested that these results emphasize the importance of the medial cerebellum, possibly by way of the fastigial nucleus, in balancing the output of the paired vestibular nuclei.

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