Abstract
Introduction: Conventional transcranial direct current stimulation (tDCS) and high-definition tDCS (HD-tDCS) may improve motor learning in children. Mechanisms are not understood. Neuronavigated robotic transcranial magnetic stimulation (TMS) can produce individualised maps of primary motor cortex (M1) topography. We aimed to determine the effects of tDCS- and HD-tDCS-enhanced motor learning on motor maps.Methods: Typically developing children aged 12–18 years were randomised to right M1 anodal tDCS, HD-tDCS, or Sham during training of their left-hand on the Purdue Pegboard Task (PPT) over 5 days. Bilateral motor mapping was performed at baseline (pre), day 5 (post), and 6-weeks retention time (RT). Primary muscle was the first dorsal interosseous (FDI) with secondary muscles of abductor pollicis brevis (APB) and adductor digiti minimi (ADM). Primary mapping outcomes were volume (mm2/mV) and area (mm2). Secondary outcomes were centre of gravity (COG, mm) and hotspot magnitude (mV). Linear mixed-effects modelling was employed to investigate effects of time and stimulation type (tDCS, HD-tDCS, Sham) on motor map characteristics.Results: Twenty-four right-handed participants (median age 15.5 years, 52% female) completed the study with no serious adverse events or dropouts. Quality maps could not be obtained in two participants. No effect of time or group were observed on map area or volume. LFDI COG (mm) differed in the medial-lateral plane (x-axis) between tDCS and Sham (p = 0.038) from pre-to-post mapping sessions. Shifts in map COG were also observed for secondary left-hand muscles. Map metrics did not correlate with behavioural changes.Conclusion: Robotic TMS mapping can safely assess motor cortex neurophysiology in children undergoing motor learning and neuromodulation interventions. Large effects on map area and volume were not observed while changes in COG may occur. Larger controlled studies are required to understand the role of motor maps in interventional neuroplasticity in children.
Highlights
Conventional transcranial direct current stimulation and highdefinition Transcranial direct current stimulation (tDCS) (HD-tDCS) may improve motor learning in children
We investigated the effects of stimulation and tDCS-enhanced motor performance on additional motor map outcomes, hotspot magnitude (MEP amplitude), and centre of gravity (COG) of both hands
One participant was excluded from the motor mapping analyses as their motor mapping intensity exceeded 100% machine stimulator output (MSO), resulting in insufficient motor evoked potential (MEP) recordings
Summary
Conventional transcranial direct current stimulation (tDCS) and highdefinition tDCS (HD-tDCS) may improve motor learning in children. Transcranial direct current stimulation (tDCS) is a non-invasive technique capable of modulating cortical excitability in humans (Nitsche and Paulus, 2000). Anodal tDCS applied simultaneously with behavioural tasks facilitates enhanced motor performance over a single session (Nitsche et al, 2003; Boggio et al, 2006; Vines et al, 2006) or across multiple sessions in healthy adults (Reis et al, 2009) with effects outlasting the stimulation period (Nitsche and Paulus, 2001; Boggio et al, 2006; Reis et al, 2009; Matsuo et al, 2011; Sohn et al, 2012; Kidgell et al, 2013). Behavioural improvements occur in healthy adults over single (Doppelmayr et al, 2016) and multiple sessions (Pixa et al, 2017) in which patterns of cortical excitability may outlast those induced by conventional tDCS (Kuo et al, 2013)
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