Prior state of cortical activity influences subsequent practicing of a visuomotor coordination task

According to the Bienenstock-Cooper-Munro (BCM) rule, a low overall cortical activity level is suggested to enhance synaptic strength of active neuronal connections, while a high level of activity should diminish it. Whereas the relevance of this mechanism for neuroplasticity in humans has been ascertained on the neurophysiological level, its functional relevance remains unclear so far. The aim of this study was to explore the impact of the pre-performance cortical activity and excitability state on subsequent performance practicing a visuomotor paradigm. Excitability of the primary motor cortex (M1) or the visual area MT/V5 was modulated by 10 min of anodal or cathodal transcranial direct current stimulation (tDCS) in healthy subjects before practice of a visuomotor tracking task. The percentage of correct tracking movements increased significantly in the early phase of practice after both anodal and cathodal stimulations over both cortical areas compared to the no-stimulation condition showing a behavioral improvement at the beginning of the practice process. Stimulation of a control cortical area did not result in significant difference with regard to the practice between cathodal, anodal and sham stimulation. However, the steepness of improvement between the different time-points was significantly increased only at the beginning of the task, and was reduced at the 5'-10' (V5) and 10'-15' (M1) time-window with regard to anodal stimulation, compared to the 'no-stimulation' condition. With regard to cathodal stimulation, the steepness of improvement was significantly lower at the 10'-15' time-window (M1) compared to the 'no-stimulation' condition. The results of our study underline the principal functional relevance of the BCM rule for the efficacy of visuomotor practice, but imply that also other mechanisms have to be taken into account.