ABSTRACT
Magnetic resonance spectroscopy (MRS) can be used in vivo to quantify metabolite concentration and provide evidence for the involvement of different neurotransmitter systems, e.g., inhibitory and excitatory, in sensory and cognitive processes. The relatively low signal-to-noise of MRS measurements has shaped the types of questions that it has been used to address. In particular, temporal resolution is often sacrificed in MRS studies to achieve sufficient signal to produce a reliable estimate of metabolite concentration. Here we apply novel analyses with large datasets to reveal the dynamics of GABA+ and Glx in the visual cortex while participants are at rest (with eyes closed) and compare this with changes in the posterior cingulate cortex. We find that the dynamic concentration of GABA+ and Glx in the visual cortex drifts in opposite directions, that is, GABA+ decreased while Glx increases over time. Further, we find that in the visual cortex, the concentration of GABA+ predicts that of Glx, such that a change in GABA+ is correlated with a subsequent opposite change in Glx. Together, these results expose novel temporal trends and interdependencies of primary neurotransmitters in the visual cortex. More broadly, we demonstrate the feasibility of using MRS to investigate in vivo dynamic changes of metabolites.