No Effect of Anodal Transcranial Direct Current Stimulation on Gamma-Aminobutyric Acid Levels in Patients with Recurrent Mild Traumatic Brain Injury

Abstract In patients in the chronic phase after recurrent mild traumatic brain injury (mTBI), alterations in gamma-aminobutyric acid (GABA) concentration and receptor activity have been reported, possibly mediating subtle but persistent cognitive deficits and increased rate of dementia in older age. We evaluated whether anodal transcranial direct current stimulation (atDCS) over the primary motor cortex reduces GABA concentration and GABAB receptor activity in patients with recurrent mTBI. Seventeen patients (mean age 25, two women) in the chronic phase after recurrent mTBI and 22 healthy control subjects (mean age 26, two women) were included. All participants received comprehensive cognitive testing and detailed questionnaires on post-concussive symptoms at baseline. Subsequently, they participated in four experimental sessions, consisting of either magnetic resonance spectroscopy (MRS)/atDCS/MRS, transcranial magnetic stimulation (TMS)/atDCS/TMS, MRS/sham/MRS, or TMS/sham/TMS to determine GABA concentr...