Perceived and mentally rotated contents are differentially represented in cortical layers of V1

Abstract

Mental rotation typically comprises perceiving an external input and subsequently mentally transforming it in the mind’s eye. These processes require feedforward and feedback information processing in visual cortex. Previous studies showed that V1 contains both the perceived and imagined representations of visual contents, posing the question how V1 can support both processes at the same time. Recent animal and human studies suggest that anatomical distinction might be key: feedforward sensory input targets the middle layer of grey matter, whereas the outer cortical layers receive feedback signals. To investigate whether perceived and mentally rotated contents are differentially represented in cortical layers of V1, we recorded 7T fMRI while participants (N=24) were briefly presented with oriented gratings and subsequently mentally rotated them. We performed depth-specific differentiation of grey matter into superficial, middle and deep layers within brain areas V1-V3 (equi-volume model). We employed pattern classification to determine shown and rotated grating orientations. Layer-specific analysis in V1 revealed differential involvement of cortical layers in perception and mental rotation, indexed by a significant interaction between cortical depth and feedforward versus feedback information flow. In detail, classification of perceived contents was higher in the middle layer than in the outer (i.e. superficial and deep) layers, whereas classification of rotated contents was higher in outer layers than in the middle layer. A similar interaction was found in V3, but not in V2. Together, this shows that perceived and mentally rotated visual contents are spatially dissociated in early visual cortex, suggesting that feedforward and feedback rely on dissociable mechanisms that manifest in distinct anatomical subregions of cortex.