Mechanisms of adaptation in macaque inferior temporal cortex R Vogels |
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KU Leuven, Belgium
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| Repetition of a stimulus reduces the responses of inferior temporal (IT) cortical neurons. Several neural models have been proposed to explain this repetition suppression or adaptation effect. We compared predictions derived from these models with adaptation effects of spiking activity in macaque IT cortex. Contrary to sharpening but in agreement with fatigue models, repetition did not affect shape selectivity. The degree of similarity between adapter and test shape was a stronger determinant of adaptation than was the response to the adapter. The spiking and LFP adaptation effects agreed with input-, but not response-fatigue models. Second, we examined whether stimulus repetition probability affects adaptation, as predicted from a top-down, perceptual expectation or prediction error model. Monkeys were exposed to 2 interleaved trials, each consisting of 2 identical (rep trial) or 2 different stimuli (alt trial). Repetition blocks consisted of 75% (25%) of rep (alt) trials and alternation blocks had the opposite repetition probabilities. For spiking and LFP activities, adaptation did not differ between these blocks. This absence of a repetition probability effect on adaptation agrees with bottom-up, fatigue-like mechanisms. Finally, we will discuss the effect of adaptation on object encoding in IT both at the single cell and population level. |
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