Abstract
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.
Acknowledgements
We are grateful to Mark Mikkelsen for sharing Matlab scripts for 1H-MRS analysis, and to Peter Hobden and Martin Stuart for assistance with scanning. Thank you also to Jon Shine and Morgan Barense for stimuli creation. The work was funded by the Wellcome Trust (Strategic Award – KSG, ADL and CJH, 104943/Z/14/Z) and Medical Research Council (KSG and CJH, G1002149). AGC’s PhD studentship was funded by the Cardiff University Neuroscience and Mental Health Research Institute.