Inhibitory mechanisms for visual form perception in the human visual cortex

Abstract

Successful visual recognition relies on our ability to extract structure from noisy sensory inputs, integrate local features into global forms and discriminate among similar objects. Previous neurophysiology studies have implicated inhibitory mechanisms in visual perception. However, the link between visual form perception and inhibitory mechanisms in the human brain remains largely unknown. Recent developments in magnetic resonance spectroscopy (MRS), enable the in-vivo measurement of low concentration metabolites such as the inhibitory neurotransmitter GABA in the human brain. Here, we investigated the relationship between GABA concentrations in visual cortex and human performance in visual form perception. We tested the observers’ ability to discriminate radial and concentric global forms (Glass patterns). We manipulated a) the amount of background noise (coarse task), and b) the similarity between global forms, using linearly morphing between concentric and radial patterns (fine task). In addition, for each participant we collected spectroscopy data using a MEGA-PRESS pulse sequence that was optimised for GABA measurements. We collected single voxel (3cm³) MRS data in occipital cortex (covering early visual areas) and occipitotemporal cortex (covering higher visual areas anterior to retinotopic cortex). We correlated GABA measurements in these voxels with performance in the coarse (i.e. detection of global patterns in noise) and fine (i.e. discrimination of highly similar global patterns) tasks. Our results showed a significant positive correlation of behavioral performance with GABA concentrations in the early visual cortex for the coarse task while a negative correlation for the fine task. No significant correlations between behavioral performance and GABA concentrations were observed in higher occipitotemporal cortex. These findings suggest that the contribution of inhibitory mechanisms to human form perception is task-dependent. In particular, increased inhibition in early visual cortex may support form segmentation from noise, while decreased inhibition may support feature integration for the discrimination of global forms.

Meeting abstract presented at VSS 2012