Regionally-specific adaptation dynamics in human object areas

Functional magnetic resonance adaptation (fMR-A, also termed repetition suppression) is a reduction in activity due to repeated image presentations which has been extensively studied in human visual areas. Here we tested whether fMR-A dynamics during sustained image presentations is determined by cortical region or by stimulus category. Nine subjects were scanned while viewing a long sustained presentation of a single face or a house image. Attentional level was maintained throughout the presentation by a demanding contrast detection task. Our results show a clear regional differentiation in adaptation dynamics within high-level visual cortex-especially in the ventral stream. Face-selective regions showed an initial adaptation effect followed by a sustained level of activity for both face and house images. In contrast, activity in house-related regions showed a faster initial decline for houses, which reached essentially to baseline for the non-optimal, face images. The object-related lateral occipital (LO) region exhibited an adaptation profile similar to the face-selective regions. Importantly, within each region, the rate of signal decline from the peak activation was independent of the viewed category (preferred or non-preferred), and this was true for parietal and frontal regions as well. Thus, our results demonstrate that the functional differentiation in ventral stream regions is evident not only in their functional selectivity but also in their adaptation dynamics. Our results suggest regional rather than stimulus specificity with regard to cortical computations. These results demonstrate that the adaptation effect can in fact be compatible with models positing a tight correlation between activity levels and perceptual states. (c) 2007 Elsevier Inc. All rights reserved.