Neurochemical correlates of scene processing in the precuneus/posterior cingulate cortex: a multimodal fMRI and 1H-MRS study

Precuneus/posterior cingulate cortex (PCu/PCC) are key components of a midline network, activated during rest but also in tasks that involve construction of scene or situation models. Despite growing interest in PCu/PCC functional alterations in disease, the underlying neurochemical modulators of PCu/PCC’s task-induced activity are largely unstudied. Here, a multimodal imaging approach was applied to investigate whether inter-individual differences in PCu/PCC fMRI activity, elicited during perceptual discrimination of scene stimuli, were correlated with local brain metabolite levels, measured during resting-state 1H-MRS. Forty healthy young adult participants (12 male) completed an fMRI perceptual odd-one-out task for scenes, objects and faces. 1H-MRS metabolites N-acetyl-aspartate (tNAA), glutamate (Glx) and γ-amino-butyric acid (GABA+) were quantified via PRESS and MEGA-PRESS scans in a PCu/PCC voxel and an occipital (OCC) control voxel. Whole brain fMRI revealed a cluster in right dorsal PCu/PCC that showed a greater BOLD response to scenes versus faces and objects. When extracted from an independently defined PCu/PCC region of interest, scene activity (versus faces and objects and also versus baseline) was positively correlated with PCu/PCC, but not OCC, tNAA. A complementary fMRI analysis restricted to the PCu/PCC MRS voxel area identified a significant PCu/PCC cluster, confirming the positive correlation between scene-related BOLD activity and PCu/PCC tNAA. There were no correlations between PCu/PCC fMRI activity and Glx or GABA+ levels. These results demonstrate, for the first time, that scene activity in PCu/PCC is linked to local tNAA levels, identifying a neurochemical influence on inter-individual differences in the task-driven activity of a key brain hub.