Towards an optimization of functional localizers in non-human primate neuroimaging with (fMRI) frequency-tagging

Beyond faces: the contribution of the amygdala to visual processing in the macaque brain

The amygdala is present in a diverse range of vertebrate species, such as lizards, rodents, and primates; however, its structure and connectivity differs across species. The increased connections to visual sensory areas in primate species suggests that understanding the visual selectivity of the amygdala in detail is critical to revealing the principles underlying its function in primate cognition. Therefore, we designed a high-resolution, contrast-agent enhanced, event-related fMRI experiment, and scanned 3 adult rhesus macaques, while they viewed 96 naturalistic stimuli. Half of these stimuli were social (defined by the presence of a conspecific), the other half were nonsocial. We also nested manipulations of emotional valence (positive, neutral, and negative) and visual category (faces, nonfaces, animate, and inanimate) within the stimulus set. The results reveal widespread effects of emotional valence, with the amygdala responding more on average to inanimate objects and animals than faces, bodies, or social agents in this experimental context. These findings suggest that the amygdala makes a contribution to primate vision that goes beyond an auxiliary role in face or social perception. Furthermore, the results highlight the importance of stimulus selection and experimental design when probing the function of the amygdala and other visually responsive brain regions.

The anterior fusiform gyrus: The ghost in the cortical face machine

Face-selective regions in the human ventral occipito-temporal cortex (VOTC) have been defined for decades mainly with functional magnetic resonance imaging. This face-selective VOTC network is traditionally divided in a posterior 'core' system thought to subtend face perception, and regions of the anterior temporal lobe as a semantic memory component of an extended general system. In between these two putative systems lies the anterior fusiform gyrus and surrounding sulci, affected by magnetic susceptibility artifacts. Here we suggest that this methodological gap overlaps with and contributes to a conceptual gap between (visual) perception and semantic memory for faces. Filling this gap with intracerebral recordings and direct electrical stimulation reveals robust face-selectivity in the anterior fusiform gyrus and a crucial role of this region, especially in the right hemisphere, in identity recognition for both familiar and unfamiliar faces. Based on these observations, we propose an integrated theoretical framework for human face (identity) recognition according to which face-selective regions in the anterior fusiform gyrus join the dots between posterior and anterior cortical face memories.