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Rufin Vogels; Mechanisms of adaptation of spiking activity and local field potentials in macaque inferior temporal cortex. Journal of Vision 2011;11(11):3. doi: 10.1167/11.11.3.
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© ARVO (1962-2015); The Authors (2016-present)
Several neural models have been proposed to explain adaptation effects in visual areas. We compared predictions derived from these models with adaptation effects of spiking activity and Local Field Potentials (LFPs) in macaque inferior temporal (IT) cortex. First, we compared the effect of brief adaptation on shape tuning using parameterized shape sets with predictions derived from fatigue and sharpening models. We found adaptation of spiking activity and of LFP power in the high-gamma (60–100 Hz) band. 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 the top-down, perceptual expectation model of Summerfield et al. (Nat. Neurosci., 2008). Monkeys were exposed to 2 interleaved trials, each consisting of 2 either identical (rep trial) or different stimuli (alt trial). Repetition blocks consisted of 75% (25%) of rep (alt) trials and alternation blocks had the opposite repetition probabilities. For both spiking and LFP activities, adaptation did not differ between these blocks. This absence of any repetition probability effect on adaptation suggests that adaptation in IT is not caused by contextual factors related to perceptual expectation, but instead agrees with bottom-up, fatigue-like mechanisms. We will discuss the implications of these single unit and LFP data for the interpretation of fMRI-adaptation studies.
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