Treatment of Parkinson's disease by cortical stimulation

Opportunities for the treatment of Parkinson's disease (PD) by cortical stimulation are open. This review outlines the main arguments for the use of cortical stimulation in PD: the widespread cortical dysfunction that could be corrected by cortical stimulation; the main mechanism of action of subthalamic nucleus stimulation that could take place within the primary motor cortex; and the ability of cortical stimulation to modulate basal ganglia activity by exciting cortico-basal ganglia projections. Such neuromodulatory effects could correspond to either stimulus-locked changes in brain rhythms or delayed changes in synaptic plasticity. Repetitive transcranial magnetic stimulation can produce transient improvement of motor performance when the primary motor cortex or the supplementary motor area is targeted. Alleviation of mood and cognitive disorders are rather observed when repetitive transcranial magnetic stimulation is applied to the dorsolateral prefrontal cortex. However, to produce more permanent therapeutic effects, chronic stimulation using surgically implanted electrodes is necessary. For this purpose, epidural implantation is safer and should be used in preference to subdural implantation. Pioneering results of epidural motor cortex stimulation in PD have been published, but they relate to case reports and open studies, precluding any definitive conclusion. Epidural cortical stimulation is easy to perform and could be a valuable therapeutic alternative to deep-brain stimulation. However, new epidural leads need to be designed before considering the development of such a technique for PD treatment.