Proton magnetic resonance spectroscopy (¹H MRS) is a well-established technique for quantifying the brain biochemistry in vivo. In most studies, however, the ¹H MRS is acquired during rest with little to no constraint on behavior. Measured metabolite levels, therefore, reflect steady-state concentrations whose associations with behavior and cognition are unclear and limited. With recent advances in MR technology, ¹H MRS is now experiencing a resurgence with growing and compelling evidence of task-related changes in brain glutamate at temporal resolution similar to fMRI. More importantly, these changes are consistent with altered metabolic steady-states that reflect the neural output driven by shifts in the local excitatory and inhibitory (E/I) balance on local circuits. Unlike blood oxygen level differences-base fMRI, this form of in vivo MRS, also known as functional MRS (¹H fMRS), yields a more direct measure of behaviorally relevant neural activity and is considerably less sensitive to vascular changes. ¹H fMRS enables noninvasive investigations of task-related glutamate changes that are relevant to normal and impaired cognitive performance, and psychiatric disorders.
This presentation will: 1) introduce ¹H fMRS and its conceptual framework in assessing the neural output driven by shifts in the E/I balance on local circuits; 2) provide evidence that ¹H fMRS is a sensitive tool for detecting task-related changes in the excitatory neurotransmitter glutamate in functionally relevant brain areas; and 3) provide evidence on how ¹H fMRS can advance the understanding of neural dysfunctions related to the inability to shift the E/I equilibrium through mechanisms of impaired synaptic plasticity in aging and psychiatric disorders.
