title: tDCS-induced alterations in GABA concentration within primary motor cortex predict motor learning and motor memory: a 7 T magnetic resonance spectroscopy study.
abstract: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that alters cortical excitability in a polarity specific manner and has been shown to influence learning and memory. tDCS may have both on-line and after-effects on learning and memory, and the latter are thought to be based upon tDCS-induced alterations in neurochemistry and synaptic function. We used ultra-high-field (7 T) magnetic resonance spectroscopy (MRS), together with a robotic force adaptation and de-adaptation task, to investigate whether tDCS-induced alterations in GABA and Glutamate within motor cortex predict motor learning and memory. Note that adaptation to a robot-induced force field has long been considered to be a form of model-based learning that is closely associated with the computation and 'supervised' learning of internal 'forward' models within the cerebellum. Importantly, previous studies have shown that on-line tDCS to the cerebellum, but not to motor cortex, enhances model-based motor learning. Here we demonstrate that anodal tDCS delivered to the hand area of the left primary motor cortex induces a significant reduction in GABA concentration. This effect was specific to GABA, localised to the left motor cortex, and was polarity specific insofar as it was not observed following either cathodal or sham stimulation. Importantly, we show that the magnitude of tDCS-induced alterations in GABA concentration within motor cortex predicts individual differences in both motor learning and motor memory on the robotic force adaptation and de-adaptation task.
authors.affiliation: Brain and Body Centre, School of Psychology, University of Nottingham, UK.
authors.forename: Soyoung
authors.initials: S
authors.lastname: Kim
authors.affiliation: Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, UK.
authors.forename: Mary C
authors.initials: MC
authors.lastname: Stephenson
authors.affiliation: Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, UK.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Morris
authors.affiliation: Brain and Body Centre, School of Psychology, University of Nottingham, UK. Electronic address: Stephen.jackson@nottingham.ac.uk.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Jackson
mesh_terms: D000223:Adaptation, Psychological; D000293:Adolescent; D000328:Adult; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D007858:Learning / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008568:Memory / Q000502:physiology*; D009044:Motor Cortex / Q000378:metabolism*; D009048:Motor Skills / Q000502:physiology; D065908:Transcranial Direct Current Stimulation; D014793:Visual Cortex / Q000378:metabolism; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid
keywords: Biological Sciences; Cognitive Sciences; Force adaptation; GABA; Magnetic resonance spectroscopy; Motor learning; Neuroscience; Psychological; tDCS