The metabolite correlates of the negative BOLD signal were investigated using functional MRS and compared to the changes produced by the positive BOLD response. The participants were scanned in a 7-T MRI while passively viewing visual checkerboards. For the positive BOLD response, increases of glutamate and lactate concentrations were observed, while the negative BOLD response in a similar voxel was linked to a decrease of glutamate, lactate and GABA concentrations. This measured decrease of oxidative metabolism during the negative BOLD response suggest a reduction a glutamatergic activity in the visual cortex.
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