Magnetic Resonance Spectroscopy (MRS)
MRS is an MR technique that allows non-invasive quantification of a variety of neurochemicals within a localised region of tissue. We have used single voxel MRS (where neurochemicals are acquired from one region of tissue only) to investigate changes in GABA and glutamate, the major cortical neurotransmitters, in response to transcranial stimulation.
In a recent study we demonstrated that GABA concentration within the primary motor cortex is related to reaction times, and further that the responsiveness of the GABAergic system to tDCS is related to the degree to which subjects are able to learn a sequence of finger presses. This suggests that the responsiveness of the GABA system may be important in the early stages of motor learning in humans.
With our collaborators Professor John Rothwell and Dr Sven Bestmann at University College London we went on to perform an MRS / TMS study to investigate the physiological basis of our MRS-derived GABA measurement. The results from this suggest that GABA concentration as measured by MRS probably reflects extrasynaptic rather than synaptic GABA activity, a finding which has important implications in our understanding of changing GABA concentration during learning or recovery after stroke.