HVGC · Imaging neural gain control in the human visual system

Gain control is a canonical neural computation that is found across the brain. Almost all models of neuronal gain propose that the activity of each neuron is normalized by the combined activity of its neighbouring neurons – a so-called ‘gain pool’. Information in the visual pathways undergoes several such normalization stages beginning in the retina and continuing through visual cortex. Gain control has been studied in animal models and using psychophysical techniques in humans but direct, quantitative measurements of neuronal activity in well-defined human visual areas has proved technically challenging. Gain control mechanisms that operate across long distances in visual space are particularly interesting to us because they must be implemented in cortex and may be sensitive markers of neurological disease.In this project, we will use a novel and innovative combination of neuroimaging techniques (functional magnetic resonance imaging (fMRI) and electrical source imaging (ESI)) together with visual psychophysics to measure the spatial, temporal and featural tuning of long-range gain control in the human visual system and relate these findings to perception.We have two objectives:1: Different types of stimuli appear to have different types of gain pools. Using electrical source imaging (ESI) and fMRI we will map the selectivity of long-range gain pools in different visual areas and examine how this selectivity affects the way that different stimuli are seen.2: Gain control changes profoundly across both space and time. We will use fMRI to examine the spatial characteristics of long-range gain control and ESI to examine its temporal characteristics. We will relate these data to perception - the ultimate goal being to predict the appearance of novel, dynamic stimuli.