Categorical selectivity in the visual pathway revealed by fMRI in awake macaques

[摘要] Neuronal activity in the primate occipito-temporal pathway has been shown to contain information about visual object category. Specifically, recent neuroimaging and electrophysiological studies have revealed that the inferior temporal (IT) cortex contains regions that encode stimuli belonging to one category compared to others. However, the majority of these studies have limited their investigations to higher parts of IT cortex, leaving earlier areas in the visual hierarchy, as well as areas within the occipito-parietal pathway, less thoroughly explored. Here, we used functional magnetic resonance imaging (fMRI) to investigate the neural encoding of object categorisation in awake behaving macaques. We employed an event-related design and presented 3 monkeys with 48 images, consisting of 24 animate (human- and animal- faces and body-parts) and 24 inanimate (objects and places) images. Monkeys were trained to fixate on a cue and received juice reward for maintaining fixation within the frame where the images were presented. For each subject, we collected approximately 1170-1521 volumes per session. We collected about 10 sessions per monkey. Regions of interest included early visual areas (V1, V2, V3, V4), category-selective regions in IT cortex (face-, object-, body-part- "patches") and dorsal-parietal regions. We used a general linear model to analyse the time series data in which we included the animals' broken fixations and head motion as nuisance regressors. Consistent with previous studies, we found that the animate-inanimate, face-body parts and the face-inanimate contrasts activated face patches. We also found voxels preferentially activated by objects vs. places in patches along the temporal cortex and, interestingly, in the intraparietal sulcus. We did not find any categorical organisation in areas V1-3, but the animate-inanimate division was observed in V4. Our results suggest that as one moves beyond the striate cortex, a network of visual areas exhibiting a categorical organisation of object representation begins to emerge.

[学科分类] 眼科学