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Kalanit Grill-Spector; fMRI-Adaptation in Human Ventral Temporal Cortex: Regional Differences Across Time Scales. Journal of Vision 2011;11(11):4. doi: 10.1167/11.11.4.
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© ARVO (1962-2015); The Authors (2016-present)
One of the most robust experience-related cortical dynamics is reduced neural activity when stimuli are repeated. This reduction has been linked to performance improvements due to repetition and also used to probe functional characteristics of neural populations. However, the underlying neural mechanisms are as yet unknown. Here, we consider two models that have been proposed to account for repetition-related reductions in neural activity, and evaluate them in terms of their ability to account for the main properties of this phenomenon as measured with fMRI (referred to as fMRI-adaptation, fMRI-A). I will describe results of recent experiments in which we investigated the effects of short-lagged (SL, immediate) and long-lagged (LL, many intervening stimuli) repetitions on category selectivity in human ventral temporal cortex (VTC) using high-resolution fMRI. We asked whether repetition produces scaling or sharpening of fMRI responses across VTC. Results illustrate that repetition effects across time scales vary qualitatively along a lateral-medial axis. In lateral VTC, both SL and LL repetitions produce scaling of fMRI responses. In contrast, medial VTC exhibits scaling effects during SL repetitions, but sharpening effects for LL repetitions. Finally, computer simulations linking neural repetition effects to fMRI-A show that different neural mechanisms likely underlie fMRI-A in medial compared to lateral VTC. These results have important implications for future fMRI-A experiments because they suggest that fMRI-A does not reflect a universal neural mechanism and that results of fMRI-A experiments will likely be paradigm independent in lateral VTC, but paradigm dependent in medial VTC.
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