Search PubMed⌕ Search

Biomedical subjects

C H Yeo

Publications and source records attributed to C H Yeo.

25 records · Page 2Linked to original sources
PubMed1984

Discrete lesions of the cerebellar cortex abolish the classically conditioned nictitating membrane response of the rabbit.

The classically conditioned nictitating membrane response (NMR) of the rabbit is useful for analyses of brain structures and pathways involved in mammalian associative learning. Lesions of the entire cerebellum, its nuclei or its efferent pathway abolish conditioned NMR learning and prevent its reacquisition. Until now it has not been clear whether the cerebellar cortex is an essential part of the circuitry for NMR conditioning. Here we report that small lesions of the cerebellar cortex in the hemispheral portion of lobule VI, with sparing of the underlying nuclei, abolish the ipsilateral conditioned NMR and prevent it from being reacquired.

Animals↗
PubMed1983

Retention of conditioned inhibition of the nictitating membrane response in decorticate rabbits.

Rabbits were trained on a Pavlovian conditioned inhibition (CI) task using light as the reinforced conditional stimulus (CS) and the same light compounded with a tone as the non-reinforced CS. The conditional response was the nictitating membrane response (NMR). The subjects then received an extensive neocortical lesion or a sham operation. After 9 weeks postoperative recovery, the animals were retrained on the CI task. Sham operated control animals showed immediate and high levels of CI retention but the decorticates showed a profound initial loss, showing that there is a cortical influence in CI. Reacquisition of CI by the decorticates was rapid and showed considerable savings over de novo acquisition. This supports our earlier finding that the neocortex is not essential for the acquisition of CI.

Animals↗
PubMed1981

The effects of unilateral frontal eye field lesions in the monkey: visual-motor guidance and avoidance behaviour.

Macaque monkeys were tested on a visual-motor guidance task and observations of avoidance behaviour were made following unilateral frontal eye field lesions. Visual-motor guidance was assessed by speed and accuracy of reaching to press recessed, illuminated buttons arrayed in a 90 degree arc in front of the monkey. Unilateral frontal eye field lesions produced a marked neglect of stimulus lights contralateral to the side of the lesions, as shown in greatly increased errors and response latencies. Responses to the most peripheral of the ipsilateral stimulus lights were also affected, although not to the same degree. Partial to complete recovery occurred, usually within a month. A unilateral lesion of the principal sulcus did not cause symptoms of neglect in the visual-motor guidance task. Section of the cerebral commissures partially restored the visual-motor guidance deficit in the frontal eye field-lesioned monkeys, with recovery again occurring. Commissurotomy and the unilateral frontal eye field lesion performed in a single-stage operation produced an initially more severe neglect than the two-stage operation, but recovery was no less rapid. The unilateral frontal eye field lesions resulted in a severe neglect of contralateral threat objects when the monkeys were threatened from both sides (avoidance-avoidance tests). Avoidance was normal when the threat was presented to one side. Commissurotomy fully restored the avoidance-avoidance deficit and made it permanent. These and other recent findings suggest that the contralateral visual field defect and the other symptoms resulting from frontal eye field lesions represent an impairment in directing and sustaining attention in regions of the visual field arising from disruption of a corticothalamotectal sensorimotor integration system.

Animals↗
PubMed1980

Conditioned inhibition of the nictitating membrane response in decorticate rabbits.

Rabbits with substantial neocortical ablation were trained in a Pavlovian conditioned inhibition task using a light as the reinforced conditioned stimulus (CS) and the same light compounded with a tone as the non-reinforced CS. The conditioned response was the nictitating membrane response, and the unconditioned stimulus was paraorbital shock. Training began 4-14 months postoperatively. With a number of procedural variations across 4 experiments, there was little evidence of impaired conditioned inhibition by decorticates compared to control animals. These results are consistent with earlier reports on Pavlovian discrimination learning and reversal involving single-element CSs from different sense modalities. Hence, they extend the basic conclusion that neocortex is not essential for Pavlovian inhibition to the conditioned inhibition paradigm. Consideration of these findings in the light of previous investigations of conditioned inhibition in rabbits, involving mesencephalic or hippocampal lesions, supports the hypothesis that the crucial neural elements for Pavlovian inhibition may be located in the brain stem.

Animals↗
PubMedDate not supplied

Acquisition of a new-latency conditioned nictitating membrane response--major, but not complete, dependence on the ipsilateral cerebellum.

Classical conditioning of the nictitating membrane response (NMR) of rabbits is simple associative learning of a motor response. In several two-stage experiments, reversible inactivations of the deep cerebellar nuclei in stage 1 appeared to prevent acquisition of NMR conditioning in naive rabbits--no conditioned responses (CRs) were evident after inactivations were lifted in stage 2. Results of a three-stage experiment were different. When subjects were first trained with a light conditional stimulus (CS) in stage 1, reversible cerebellar inactivations during conditioning to a different, tone CS during stage 2 did not appear to prevent new learning because CRs to the tone CS were evident when the inactivation was lifted. Results from the two-stage experiments support the suggestion that the cerebellum is essential for the acquisition of NMR conditioning, but results from the three-stage experiment do not. Here, we use a three-stage design with different interstimulus intervals (ISIs) in stages 1 and 2. Because CRs develop with latencies-to-peak dependent on the ISI, learning during stage 1 can be dissociated from that accruing in stage 2. Complete inactivation of the ipsilateral cerebellar nuclei with muscimol substantially but not completely prevented learning with the second ISI during stage 2 because small CR peaks around the stage 2 ISI could be detected in some subjects after the inactivation had been lifted in stage 3. We suggest that the weak levels of conditioning possible during unilateral inactivation depend on the contralateral cerebellum or on extracerebellar circuitry and that these may be capable of supporting transfer of conditioning in a previous three-stage experiment. But, we confirm that normal NMR conditioning is critically dependent on the ipsilateral cerebellum.

Animals↗