Abstract
The orientation of a visual grating can be decoded from human primary visual cortex (V1) using functional magnetic resonance imaging (fMRI) at conventional resolutions (2-3 mm voxel width, 3T scanner). It is unclear to what extent this information originates from different spatial scales of neuronal selectivity, ranging from orientation columns to global areal maps. According to the global-areal-map account, fMRI orientation decoding relies exclusively on fMRI voxels in V1 exhibiting a radial or vertical preference. Here we show, by contrast, that 2-mm isotropic voxels in a small patch of V1 within a quarterfield representation exhibit reliable opposite selectivities. Sets of voxels with opposite selectivities are locally intermingled and each set can support orientation decoding. This indicates that global areal maps cannot fully account for orientation information in fMRI and demonstrates that fMRI also reflects fine-grained patterns of neuronal selectivity.
Significance statement Conventional (3T) functional magnetic resonance imaging (fMRI) allows one measure brain activity at a spatial resolution of 2-3 mm. Brain response patterns in the primary visual cortex (V1) measured with fMRI have been shown to contain robust information about the orientation of visual grating stimuli. However, it is unclear whether this information arises only from global-areal patterns or also from more fine-grained patterns. Here we show that opposite orientation preferences are present and replicable within small V1 patches. This finding demonstrates that fine-grained fMRI patterns contribute to the orientation information present in fMRI data.
