Neurophysiology of sensorimotor integration in Parkinson's disease.

Parkinson's disease (PD) is a major neurologic disorder that distinctively and selectively affects movement and--by extension--the motor system. A large body of evidence has been accumulated over the years showing that movement disorders of PD are also due to sensory disturbances that affect sensorimotor integration. The aim of this review is to discuss the possible contribution of neurophysiologic techniques in evaluating the functionality of sensorimotor integration mechanisms in PD. Somatosensory evoked potentials (SEPs) are an appropriate functional approach for the evaluation of sensory processes in the human brain. SEPs from the frontal scalp sites are considered markers of the functionality of a cortico-subcortico-cortical loop that includes the basal ganglia as well as the premotor and supplementary motor areas. Over the years, it has been demonstrated that PD patients--especially in the early stages of the disease--show a severely depressed frontal responsiveness to sensory stimuli as tested via SEPs. The transient recovery of frontal SEP amplitude after apomorphine, a potent dopamine agonist drug, is a good and specific predictor of the clinical response of PD patients to L-dopa therapy.