Biomedical subjects

M J Eacott

Publications and source records attributed to M J Eacott.

23 records · Page 2Linked to original sources

PubMed1991

The role of monkey inferior parietal cortex in visual discrimination of identity and orientation of shapes.

Three cynomolgus monkeys (Macaca fascicularis) were tested for their visual learning ability following bilateral lesions to the inferior parietal cortex. In discrimination learning with patterns differing from each other in form and colour their performance was normal. In discriminating monochromatic patterns their performance depended on the nature of the pattern discrimination; when the discriminanda were different shapes (e.g. x,v) they performed well, while with discriminanda which differed only in the orientation of the shape (e.g. p,d) they performed relatively badly. These results were compared to the previously reported results of normal animals and animals with inferior temporal lesions performing the same task. The ratio of errors in orientation discrimination to errors in shape discrimination was significantly higher than normal in the group with parietal lesions, and significantly lower than normal in the group with inferior temporal lesions. These results suggest that the roles of inferior temporal and inferior parietal cortex in the discrimination of shape and orientation are complementary.

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PubMed1990

Interhemispheric transfer of visuomotor conditional learning via the anterior corpus callosum of monkeys.

Two experiments examined interhemispheric transfer of learning across the anterior corpus callosum in monkeys (Macaca fascicularis). The animals learned a series of visuomotor conditional discrimination problems for food reward. Within each problem the animals were first trained using one hand to make the motor responses, and were then required to use the opposite hand in order to test for intermanual transfer of the initial learning. In Exp. 1, a group of animals with surgical section of the entire corpus callosum and anterior commissure showed a complete absence of intermanual transfer of learning. A second group, in which only the anterior commissure and the posterior part of the corpus callosum were sectioned, leaving the anterior corpus callosum intact, showed good intermanual transfer. Thus, intermanual transfer in the second group represented interhemispheric information transfer via the anterior portions of the corpus callosum. However, in Expt. 2, normal intermanual transfer was seen in a group of animals in which the anterior corpus callosum alone had been sectioned. We conclude that the anterior corpus callosum can mediate interhemispheric transfer of visuomotor conditional learning, but is not the only available route for such transfer in the present task.

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PubMed1989

Interhemispheric transfer of visual learning in monkeys with intact optic chiasm.

The purpose of the present experiments was to investigate the role of the forebrain commissures in interhemispheric visual transfer when both eyes are open and the optic chiasm is intact. Cynomolgus monkeys (Macaca fascicularis) learned a series of two-choice simultaneous visual discriminations. The visual stimuli were bipartite, with independently determined left and right halves. If such a stimulus is fixated centrally, the two halves fall into opposite visual hemifields. After 10 trials of acquisition of each discrimination, the same discriminanda were presented for a further 10 trials in which, within each stimulus, the positions of the halves were exchanged: the left half became the right and vice versa. The unoperated animals transferred well to the altered stimuli, making many fewer errors than they made in learning the originally presented discrimination. In contrast, monkeys with section of the posterior corpus callosum and the anterior commissure transferred poorly. These effects show that the forebrain commissures are important for the interhemispheric transfer and integration of visual information in animals with a normal, intact peripheral visual system.

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PubMed1989

Reaching to a rewarded visual stimulus: interhemispheric conflict and hand use in monkeys with forebrain commissurotomy.

Monkeys (Macaca fascicularis) learned simultaneous visual discriminations for food reward. Two coloured patterns were presented one above the other and the monkey chose one by touching it with a hand. On some trials, conflicting information was presented to the two visual hemifields. For example, in the left hemifield the stimulus associated with reward was in the higher position and in the right hemifield the stimulus associated with reward was in the lower position. On some of these conflict trials the monkeys were required to use the left hand and on others the right. Normal monkeys, monkeys with section of the anterior commissure and the posterior corpus callosum, and monkeys with section of the anterior commissure and the whole of the corpus callosum performed this task. Our aim was to test the hypothesis that following forebrain commissurotomy, the response made by each hand would be predominantly influenced by the visual information put into the hemisphere contralateral to that hand. If this is true then choices in the conflict test should vary systematically with hand use. This hypothesis was not confirmed. We conclude that when a monkey reaches to a rewarded visual stimulus, information about the reward history of the stimulus is integrated between the hemispheres before influencing the motor control of the hand that reaches, either by a peripheral or a subcortical route.

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PubMedDate not supplied

The roles of perirhinal cortex, postrhinal cortex, and the fornix in memory for objects, contexts, and events in the rat.

Investigation of the anatomical substructure of the medial temporal lobe has revealed a number of highly interconnected areas, which has led some to propose that the region operates as a unitary memory system. However, here we outline the results of a number of studies from our laboratories, which investigate the contributions of the rat's perirhinal cortex and postrhinal cortex to memory, concentrating particularly on their respective roles in memory for objects. By contrasting patterns of impairment and spared abilities on a number of related tasks, we suggest that perirhinal cortex and postrhinal cortex make distinctive contributions to learning and memory: for example, that postrhinal cortex is important in learning about within-scene position and context. We also provide evidence that despite the strong connectivity between these cortical regions and the hippocampus, the hippocampus, as evidenced by lesions of the fornix, has a distinct function of its own--combining information about objects, positions, and contexts.

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