tDCS-induced alterations in GABA concentration within primary motor cortex predict motor learning and motor memory: A 7T 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.

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…The majority of these studies investigated neurometabolite changes in the motor cortex in young adults, reporting a consistent reduction of GABA after atDCS [31, 70, 75, 76], except for Tremblay et al [77]. The above finding was generally coupled with increased FC over the motor network [31, 39], indicating that these connectivity changes may be driven by a decrease in the inhibitory neurotransmitter.…”

“…Indeed, Stagg et al [76] estimated a decrease of around 12% of GABA levels in the motor cortex following motor atDCS and an inverse correlation with motor network FC [39]. Conversely, the effects of ctDCS on brain metabolites levels are less clear, one study reporting no effect [75], and one decreased GABA and Glu levels [70]. Age may modulate the effects of NIBS on brain neurometabolites.…”

Impact of Transcranial Direct Current Stimulation (tDCS) on Neuronal Functions

“…Primary motor-cortex atDCS reduced local gamma-aminobutyric acid (GABA) concentration (Stagg et al, 2009; Kim et al, 2014) whereas ctDCS reduced both glutamate (Glu) and GABA concentrations in human cortex (Stagg et al, 2009). In contrast to Stagg et al (2009), in which stimulation was performed at rest, Kim et al (2014) observed no ctDCS effect on GABA when subjects were performing a motor adaptation task. Therefore, tDCS effects on neurotransmitter concentration may be task specific.…”

P244 The effect of transcranial direct current stimulation on motor sequence learning and upper limb function after stroke

“…This is consistent with the findings of Hummel et al (2005) that JTT improvements persisted for at least 25 minutes after anodal tDCS. Changes in cortical excitability and intracortical inhibition have also been shown to persist after the stimulation is turned off (Ardolino et al , 2005, Stagg et al , 2009, Di Lazzaro et al , 2012, Bastani et al , 2013b, a, Kidgell et al , 2013, Kim et al , 2014, Moliadze et al , 2014.…”