Neuromodulation with transcranial direct current stimulation : the influence of electrode arrangement

• Main Author: Fleming, Melanie Kate
• Other Authors: Pavlou, Marousa ; Newham, Dianne
• Published: King's College London (University of London) 2017
• Subjects: 612.8
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.718534

Transcranial direct current stimulation (tDCS) could improve plasticity and motor function, but the influence of electrode arrangement is unclear. The aim of this PhD was to develop and utilise a sequential learning paradigm involving gross movements of the hand to assess the effect of tDCS electrode arrangement on; i) motor sequence learning in healthy young and older adults, ii) motor sequence learning and upper limb function in chronic stroke survivors and iii) retention of learning in healthy adults, and to determine whether the response to tDCS is dependent on changes in transcallosal inhibition (TCI). Study one tested the motor sequence learning paradigm. Young adults, stroke survivors and age-matched controls all demonstrated improvements in motor preparation with 25 repetitions of a movement sequence. However, stroke survivors showed impaired sequence specific learning. Study two demonstrated that healthy ageing was associated with reduced motor sequence learning, but tDCS did not affect performance for either younger or older adults. Bihemispheric tDCS led to an increase in TCI (ipsilateral silent period duration) for the younger group only. There were no significant relationships between changes in TCI and learning. Study three demonstrated a significant effect of tDCS electrode arrangement on upper limb function in stroke survivors, with improvements after unilateral tDCS (anodal or cathodal), but not after bihemispheric. However, there was no effect of tDCS on motor sequence learning or the change in TCI from either hemisphere. Study four showed no effect of tDCS on 48 hour retention of learning for healthy adults. However, cathodal tDCS delivered during training impaired later re-learning of the movement sequence. The findings of these studies suggest that tDCS does not improve learning of a sequence of gross hand movements. High variability in response is observed and there is no consistent effect of tDCS on TCI.