Glutamate-Weighted Magnetic Resonance Imaging (GluCEST) Detects Effects of Transcranial Magnetic Stimulation to the Motor Cortex

Abstract

Transcranial magnetic stimulation (TMS) is used in several FDA-approved treatments and, increasingly, to treat neurological disorders in off-label uses. However, the mechanism by which TMS causes physiological change is unclear, as are the origins of response variability in the general population. Ideally, objective in vivo biomarkers could shed light on these unknowns and eventually inform personalized interventions. Continuous theta burst stimulation (cTBS) is a form of TMS which has been observed to reduce motor evoked potentials (MEPs) for 60 minutes or longer post-stimulation, although the consistency of this effect and its mechanism continue to be under debate. Here, we use glutamate-weighted chemical exchange saturation transfer (gluCEST) magnetic resonance imaging (MRI) at ultra-high magnetic field (7T) to measure changes in glutamate concentration at the site of cTBS. We find that gluCEST signal in the ipsilateral hemisphere of the brain generally decreases in response to cTBS, whereas consistent changes were not detected in the contralateral or in subjects receiving a sham stimulation. One Sentence SummaryWe used glutamate-weighted Chemical Exchange Saturation Transfer (GluCEST) imaging to detect changes in glutamate contrast in the brains of young, healthy adults undergoing transcranial magnetic stimulation (TMS) to the motor cortex.