Increased visual stimulation systematically decreases activity in posterior superior temporal cortex

Previous fMRI studies have ascribed different roles to the posterior superior temporal cortex (pSTC). Some studies described a visually driven selectivity for biological motion and facial features in this region. Other studies showed a subdivision of the default mode network (DMN) in this general region, emphasizing internal (i.e. non-sensory) influences, including self-referential processing and theory of mind. To clarify the relationship between these differently-defined regions within pSTC, and the transition between sensory vs. non-sensory (i.e. external versus internal) processing here, we measured fMRI responses to systematic changes in exogenously driven salience, produced by varying the extent of stimulated visual field. Unlike the responses in occipito-temporal visual cortex, posterior Superior Temporal Cortex (pSTC) showed a paradoxically increased response to decreases in visual stimulus extent, based on variations in either object size or number. Such changes are consistent with a focus on internal (rather than external/sensory) processing in this region, as described for the DMN. Such inverted visual size responses were found across multiple categories of familiar objects and computer generated shapes, and this finding was independent of stimulus eccentricity. Testing the inverted size function across different states of spatial attention, we found that spatially distributed attention enhanced the size-inverted response in pSTC compared to centrally focused attention. Other experiments and a meta-analysis demonstrated partially overlapping subregions in pSTC based on previously reported functions (e.g. biological motion, facial features, and theory of mind), all sharing an inverted size preference. This suggests a combination of functions in pSTC, having in common a DMN-like bias against stronger visual salience. Consistent with a transitional function between sensory and more dominant non-sensory influences, pSTC showed strong functional connectivity with frontoparietal brain regions including mPFC and PCC, plus a weak but convergent connection with classic visual cortex. Interestingly, similar fMRI tests in monkeys based on analogous stimuli and tasks did not reveal a functional homologue of pSTC. This apparent discrepancy between the two species is consistent with the idea that DMN-like processing (including self-referential thinking and theory of mind) are relatively more prominent in humans, compared to macaques.status: publishe