The use of magnetic resonance spectroscopy as a tool for the measurement of bi-hemispheric transcranial electric stimulation effects on primary motor cortex metabolism.

Transcranial direct current stimulation (tDCS) is a neuromodulation technique that has been increasingly used over the past decade in the treatment of neurological and psychiatric disorders such as stroke and depression. Yet, the mechanisms underlying its ability to modulate brain excitability to improve clinical symptoms remains poorly understood(33). To help improve this understanding, proton magnetic resonance spectroscopy (H-1-MRS) can be used as it allows the in vivo quantification of brain metabolites such as gamma-aminobutyric acid (GABA) and glutamate in a region-specific manner(41). In fact, a recent study demonstrated that H-1-MRS is indeed a powerful means to better understand the effects of tDCS on neurotransmitter concentration(34). This article aims to describe the complete protocol for combining tDCS (NeuroConn MR compatible stimulator) with H-1-MRS at 3 T using a MEGA-PRESS sequence. We will describe the impact of a protocol that has shown great promise for the treatment of motor dysfunctions after stroke, which consists of bilateral stimulation of primary motor cortices(27,30,31). Methodological factors to consider and possible modifications to the protocol are also discussed.