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David K Chelvanayagam, Daniel Zaksas, Tatiana Pasternak; Activity in MT neurons is affected by the nature of motion discrimination required by the working memory task. Journal of Vision 2003;3(9):406. doi: 10.1167/3.9.406.
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© ARVO (1962-2015); The Authors (2016-present)
We recently showed that in a delayed match-to-sample task many MT neurons not only respond to the motion of sample and test stimuli but are also active in the delay period between them, while the monkey remembers the sample. This delay activity, consisting of brief activation early in the 1.5″ delay, subsequent prolonged inhibition and reactivation shortly before the onset of the test, reflects the direction of the preceding sample. We now report that certain attributes of this delay activity are associated with the monkeys' behavioral choices. Namely, trials resulting in errors contained early delay activation that was significantly weaker and shorter in duration than in trials resulting in a correct answer. Furthermore, we found that attributes of delay activity can be influenced by the nature of the discrimination task. We analyzed neuronal activity under identical sensory conditions during two tasks with somewhat different cognitive demands. In the direction range task, the monkeys were required to extract the net direction of random dots moving in a range of local vectors and compare it to a test stimulus where all dots moved in the same or opposite direction. The second task tested the accuracy with which the sample direction could be retained and compared to a test that moved in the same or slightly different direction. Although in both tasks the activity during all phases of the delay was affected by the direction of the preceding sample, there were notable differences in its temporal pattern. During the accuracy task, early activation was substantially shorter, occurred earlier and was followed by middle inhibition that ended earlier than during the range task. Our results suggest that MT activity during the memory delay is actively linked with the mechanisms that underlie storage of motion direction and task performance, and that its specific contribution to these mechanisms depends on the nature of the motion discrimination.
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