Goal-directed visual information processing with GABAergic inhibition in parietal cortex

Goal-directed visual information processing involves tracking relevant visual signals (targets) over space and time. However, goal-irrelevant visual signals (distractors) can interfere with the tracking of targets. The neural mechanisms, which promote the tracking of targets in the challenge of interference from distractors remain elusive. Here, we used time-resolved functional magnetic resonance spectroscopy (fMRS) to measure concentrations of γ-aminobutyric acid (GABA), a chief inhibitory neurotransmitter, and glutamate, a chief excitatory neurotransmitter, in parietal and visual cortex while participants performed a visual tracking task for targets among distractors. We found that the more targets had to be tracked, the greater the concentrations of GABA and glutamate in parietal cortex. In visual cortex only the concentration of glutamate increased with the number of targets. Concentration changes of GABA and glutamate only in parietal cortex were differentially associated with tracking performance: Better target tracking was associated with greater increase in GABA concentration and smaller increase in glutamate concentration. The results of control experiments showed that this differential association between tracking performance and metabolite changes in parietal cortex reflected individual differences in distractor suppression: participants with better distractor suppression during tracking tended to have greater increase in GABA concentration and smaller increase in glutamate concentration. This suggests that target-distractor interference during tracking is minimized by GABAergic suppression of goal-irrelevant distractors in parietal cortex, thereby promoting goal-directed visual information processing.