Enhancement of neuroplasticity by cortical stimulation

There is evidence that behavioural gains made by patients undergoing neurorehabilitation depend at least in part on training-induced synaptic plasticity. Non-invasive cortical stimulation induces changes in synaptic strength in healthy humans which outlast the period of stimulation, and therefore may interact with and potentially enhance the process of rehabilitation in patients. Repetitive transcranial magnetic stimulation can reduce motor cortex excitability at low frequencies or increase it at high frequencies. Anodal transcranial direct current stimulation can increase excitability while cathodal stimulation can reduce it.. Brain stimulation has mainly been examined in patients with stroke, aiming to increase excitability in the stroke hemisphere or reduce it in the contralesional hemisphere. Beneficial effects have been reported but it has proved difficult to reproduce results with greater numbers. This likely reflects a lack of understanding of stimulation mechanisms, high response variability with current protocols, and the diversity of protocols tested.These issues must be resolved before brain stimulation can enter clinical practice.