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Abstract:
In traditional functional magnetic resonance imaging (fMRI) carefully controlled stimuli are used to reveal cortical regions that are differentially responsive to distinct stimuli. In human fMRI studies we have shown that the varying intensity of features, such as faces or color, seen in a movie, can be used to map feature selective regions, such as the human V4 complex for color or superior temporal regions (STS) and lateral fusiform cortex (FFA) for faces (Bartels amp;amp; Zeki, 2004). Here we applied the same paradigm in the anesthetized monkey to identify regions involved in processing various low- and high-level features. The advantage of this approach is that effects of attention or eye-movements can be excluded. We found that the BOLD signal in V1 was best predicted by changes in frame-by-frame pixel intensities (contrast changes) compared to measures of contrast, luminance or spatial frequency. BOLD signal in response to contrast changes were specific enough to reveal the retinotop
y of
V1
and V2 as a function of their spatial location throughout the movie. Color variations correlated most with BOLD signal in V4 and weakly along the STS. Face specific responses extended along the STS, and overlapped partly with the regions also responsive to color. We conclude that, in monkey as in man, movies - even though uncontrolled - allow surprisingly specific mapping of high- as well as low-level features, down to retinotopy. In addition, regions identified this way may reflect more realistically processing in natural, more complex and dynamic environments.
