ID 217 – Transcranial direct current stimulation effects on the ipsilateral proximal upper limb are movement-frequency dependent

Abstract

The aim of this work was to explore whether selective muscle activation of the biceps brachii (BB) is modified by cathodal transcranial direct current stimulation (c-tDCS) in a movement frequency-dependent manner. Seventeen healthy participants were asked to perform repetitive isometric elbow flexion and forearm pronation at 0.75, 1.0, and 1.25 Hz, paced by an auditory metronome, before and after c-tDCS (1 mA, 15 min) applied to the primary motor cortex (M1) ipsilateral to the task side. Selectivity in the modulation of corticomotor excitability was expressed as a ratio of motor evoked potential (MEP) size in BB immediately before forearm pronation task relative to elbow flexion. Transcranial magnetic stimulation delivered to the right M1 representation of the left BB at 130% of active motor threshold either 150 or 200 ms prior to every fifth metronome beat. Cathodal tDCS over the ipsilateral M1 significantly improved MEP selectivity ratios in a frequency dependent manner primarily through selective suppression of the BB antagonist (i.e., during forearm pronation). Cathodal tDCS reduced the MEP selectivity ratio for movement-frequencies of 1.0 and 1.25 Hz but not 0.75 Hz compared to sham. Cathodal tDCS is capable of improving selective muscle activation of the ipsilateral proximal upper limb in a frequency-dependent manner.