Abstract
A number of functional magnetic resonance imaging (fMRI) studies in humans have shown a decrease of neural activity in many areas of the occipito-temporal cortex when identical faces are repeated as compared to different faces. This adaptation effect has been used to infer that these areas are sensitive to differences between faces. More recently, a network of face patches have been identified in the monkey inferior temporal (IT) cortex using fMRI. In this study we tested whether these areas in monkey IT also show a decrease of activation when an individual face is repeated. The second purpose was to determine the optimal stimulation frequency rate at which such an effect would be observed. First, a whole-brain localizer was run on three monkeys, using the contrast agent enhanced fMRI technique. In agreement with previous studies, a comparison between faces and objects yielded multiple patches of activation in the superior temporal sulcus (STS). The subsequent fMR-adaptation experiment was comprised of 24 conditions (12 with an identical face; 12 with different faces). In each of these conditions, a face appeared and disappeared through a gray screen at a variable rate of stimulation (1-12 Hz). In an identical face condition, the same face was presented repeatedly. In a different faces condition, 10 individual faces appeared in a random order. All of the functionally defined face patches showed a larger response to blocks of different faces than when the same face was repeated. These effects were generally the largest when faces were presented at a rate of 5 Hz to 7 Hz suggesting that the face processing network was most sensitive to differences between faces when they were presented at these frequency rates. Electrophysiological experiments have been designed to investigate the response of single units in these fMRI defined patches, during this repeated stimulation task.
Meeting abstract presented at VSS 2013