Published Paper: Journal of Neuroscience

We are pleased to announce the publication of a recent paper by previous DPhil student Velicia Bachtiar and current DPhil student Ainslie Johnstone.   The data for this paper was collected by Velicia as part of her DPhil and subsequently analysed jointly by Velicia and Ainslie.

The paper, entitled "Modulating regional motor cortical excitability with non-invasive brain stimulation results in neurochemical changes in bilateral motor cortices" is published in the Journal of Neuroscience, and is available online now.

Congratulations to all of the authors: Velicia Bachtiar, Ainslie Johnstone, Adam Berrington, Clarke Lemke, Heidi Johansen-Berg, Uzay Emir and Charlotte Stagg

about this paper

Learning of new motor skills depends on modulation both within and between brain regions. Here, we use a novel two-voxel magnetic resonance spectroscopy (MRS) approach to quantify GABA and glutamate changes concurrently within the left and right M1 during three commonly used tDCS montages, anodal, cathodal, and bilateral. We also examined how the neurochemical changes in the unstimulated hemisphere were related to white matter microstructure between the two M1s. Our results provide insights into the neurochemical changes underlying motor plasticity, and may therefore assist in the development of further adjunct therapies.

Abstract

Learning a novel motor skill is dependent both on regional changes within the primary motor cortex (M1) contralateral to the active hand, and also on modulation between and within anatomically-distant but functionally-connected brain regions. Inter-regional changes are particularly important in functional recovery after stroke, where critical plastic changes underpinning behavioural improvements are observed in both ipsilesional and contralesional M1s. It is increasingly understood that reduction in γ-aminobutyric acid (GABA) in the contralateral M1 is necessary to allow learning of a motor task. However, the physiological mechanisms underpinning plasticity within other brain regions, most importantly the ipsilateral M1, are not well understood. Here, we used concurrent two-voxel magnetic resonance spectroscopy (MRS) to simultaneously quantify changes in neurochemicals withinleft and right M1s, in healthy humans of both sexes, in response to transcranial direct current stimulation (tDCS) applied to left M1. We demonstrated a decrease in GABA in both the stimulated (left) and non-stimulated (right) M1 after anodal tDCS, whereas a decrease in GABA was only observed in non-stimulated M1 after cathodal stimulation. This GABA decrease in the non-stimulated M1 during cathodal tDCS was negatively correlated with microstructure of M1:M1 callosal fibres, as quantified by diffusion MRI, suggesting that structural features of these fibres may mediate GABA decrease in the unstimulated region. We found no significant changes in glutamate. Taken together, these findings shed light on interactions between the two major network nodes underpinning motor plasticity, offering a potential framework from which to optimise future interventions to improve motor function after stroke.