The role of excitatory processes in human visual learning has been well characterised through the use of technologies such as functional magnetic resonance imaging (fMRI). However, established imaging modalities do not distinguish excitatory processes from the inhibitory ones that are also involved. Here we investigate inhibitory processes using magnetic resonance spectroscopy (MRS) and the MEGA-PRESS pulse sequence. We measure concentrations of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in different brain regions as functional markers of inhibitory potential. We then investigate the correlations between GABA concentrations and psychophysical learning metrics. We detail a full analysis pipeline that improves the accuracy of in vivo GABA quantification and introduce new scaling methods to resolve the grey matter contribution to metabolite measurements. We develop visual learning experiments that are mediated by training difficulty, which we link to inhibitory processes across different time scales. We also present novel evidence for GABAergic inhibitory mechanisms across multiple brain areas using fine and coarse discrimination tasks. Our results support a cooperative top-down and bottom-up model of visual learning in occipital and frontal cortical regions. Our findings reveal chemical interactions with cognition to contribute to our understanding of inhibitory processes in the human learning brain
