Biomedical subjects

Philip G F Browning

Publications and source records attributed to Philip G F Browning.

4 recordsLinked to original sources

PubMed2006

Frontal-temporal disconnection abolishes object discrimination learning set in macaque monkeys.

Two previous studies have shown that frontal-temporal disconnection in monkeys, produced by unilateral ablation of frontal cortex in one hemisphere and of visual inferior temporal cortex in the opposite hemisphere is entirely without effect on visual object-reward association learning in concurrent discrimination tasks. This is a surprising finding in light of the severe impairments that follow frontal-temporal disconnection in many other tests of visual learning and memory, including delayed matching-to-sample and several conditional learning tasks. To explore the limits of this preserved object-reward association learning, we trained monkeys on visual object discrimination learning set (DLS) prior to frontal-temporal disconnection. As a result of training with single object-reward associations, the monkeys acquired a proficient learning set, evidenced by the rapid learning of new single object-reward association problems. This rapid learning was not affected by unilateral ablations of either inferior temporal cortex alone or frontal cortex alone but was severely impaired after final surgery to complete the disconnection. Moreover, each individual monkey now learned single object-reward association problems at the slow rate at which that individual had learned such problems before the formation of learning set. This result shows that frontal-temporal disconnection abolishes visual learning set.

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PubMed2005

The role of prefrontal cortex in object-in-place learning in monkeys.

Previous ablation studies in monkeys suggest that prefrontal cortex is involved in a wide range of learning and memory tasks. However, monkeys with crossed unilateral lesions of frontal and temporal cortex are unimpaired at concurrent object-reward association learning but are impaired at conditional learning and the implementation of memory-based performance rules. We trained seven monkeys preoperatively on an associative learning task that required them to associate objects embedded in unique complex scenes with reward. Three monkeys then had crossed unilateral lesions of frontal and inferior temporal cortex and the remaining monkeys had bilateral prefrontal cortex ablation. Both groups were severely impaired postoperatively. These results show that both bilateral prefrontal cortex ablation and frontal-temporal disconnection impair associative learning for objects embedded in scenes. The results provide evidence that the function of frontal-temporal interactions in memory is not limited to conditional learning tasks and memory-dependent performance rules. We propose that rapid object-in-place learning requires the interaction of frontal cortex with inferotemporal cortex because visual object and contextual information which is captured over multiple saccades must be processed as a unique complex event that is extended in time. The present results suggest a role for frontal-temporal interaction in the integration of visual information over time.

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PubMed2004

Learning and retrieval of concurrently presented spatial discrimination tasks: role of the fornix.

In macaque monkeys (Macaco mulatta), memory for scenes presented on touch screens is fornix dependent. However, scene learning is not a purely spatial task, and existing direct evidence for a fornix role in spatial memory comes exclusively from tasks involving learning about food-reward locations. Here the authors demonstrate that fornix transection impairs learning about spatial stimuli presented on touch screens. Using a new concurrent spatial discrimination learning task, they found that fornix transection did not impair recall of preoperatively learned problems. Relearning, on the other hand, was mildly impaired, and new learning was strongly impaired. New learning of smaller sets of harder problems was also markedly impaired, as was spatial configured learning. This pattern supports a functional specialization according to stimulus domain in the medial temporal lobe.

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PubMed2004

Entorhinal cortex contributes to object-in-place scene memory.

Four rhesus monkeys (Macaca mulatta) were trained preoperatively in a test of object-in-place scene memory. They were presented daily with lists of unique computer-generated scenes each containing a spatial array of multiple individual objects. Within each scene, objects to be discriminated appeared in the foreground, each occupying a unique location, and monkeys were required to correctly discriminate the rewarded object to receive a food reward. Once this preoperative criterion was attained, the monkeys received bilateral entorhinal cortex ablation performed as either one or two surgical operations with a period of testing following each. Postoperatively, they were significantly impaired in learning new object-in-place scene problems. These results show that the entorhinal cortex, like anatomically related structures including the perirhinal cortex and the fornix, contributes to object-in-place scene learning.

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