Functional Magnetic Resonance Spectroscopy Study of Total Glutamate and Glutamine in the Human Visual Cortex Activated by a Short Stimulus

Abstract—Glutamate+glutamine (Glx) dynamics with 2s time resolution in the human occipital cortex in response to short visual stimulation was studied using functional magnetic resonance spectroscopy (fMRS) at 3 T. The dynamic changes in the Glx level and the BOLD signal were acquired in response to a 3 s flickering checkerboard in the occipital cortex of 25 volunteers. Glx concentration increased at 1 s and 15 s after the stimulus presentation. No correlation between the amplitude of the BOLD response and the change in Glx was found. The time course of changes in the total glutamate+glutamine level after the stimulus does not correspond to the turnover rate of the glutamine-glutamate cycle, but is consistent with the temporal characteristics of the vesicular cycle: the release of glutamate from vesicles and its reuptake. Thus, it can be assumed that the observed dynamics of glutamate and glutamine is not due to metabolic transformations in the neurotransmitter cycle, but due to a change in the mobility of glutamate upon exit from the vesicles and its re-entering back.