Temporal dynamics of GABA and Glx in the visual cortex

Abstract

Magnetic resonance spectroscopy (MRS) can be used in vivo to quantify neurometabolite 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 neurometabolite concentration. Here we apply novel analyses with large datasets from human participants (both sexes) to reveal the dynamics of GABA+ and Glx in visual cortex while participants are at rest (with eyes closed) and compare this with changes in posterior cingulate cortex. We find that the dynamic concentration of GABA+ and Glx in visual cortex drifts in opposite directions, that is, GABA+ decreases while Glx increases over time. Further, we find that in visual, but not posterior cingulate cortex, the concentration of GABA+ predicts that of Glx 120 s later, 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 visual cortex. More broadly, we demonstrate the feasibility of using MRS to investigate in vivo dynamic changes of neurometabolites. SIGNIFICANCE STATEMENTUsing large datasets of magnetic resonance spectroscopy acquisitions from human participants, we develop novel analyses to investigate the temporal dynamics of neurometabolite concentration in visual cortex. We find that while participants are at rest, the concentration of GABA+ and Glx drifts in opposite directions, that is, GABA+ decreases while Glx increases over time. Further, we find that the concentration of GABA+ predicts that of Glx 120 s later, such that a change in GABA+ is correlated with a subsequent opposite change in Glx. We show these phenomena are regionally localized to visual cortex.