Study of central motor functions using magnetic stimulation in Parkinson's disease

The pathophysiological abnormalities, the contribution of activity of facilitatory and inhibitory systems to muscle rigidity and hypokinesia in Parkinson's disease are not clarified in details. Transcranial magnetic stimulation of the motor cortex may provide useful data on the functional state of motor output of the central motor structures and on the functional condition of the intracerebral motor network. The abnormalities of the central motor functions and the modifying effect of L-dopa treatment in Parkinson's disease are the objectives of our study. Patients with Parkinson's disease were examined before and after L-dopa treatment. Transcranial and cervical magnetic stimulation were performed and the latency and amplitude of the motor evoked potentials from the first dorsal interosseus muscle, the central motor conduction time and the duration of cortical inhibition were measured. The motor latency and the silent period in patients before treatment were significantly shorter than those of the age-matched healthy controls. After six months of L-dopa substitution both motor latencies and silent periods increased and approached the normal values. The observed changes are thought to be in relation to the mechanisms originating in the basal ganglia and acting through inhibitory thalamo-cortical connections at cortical level and through rubro- and reticulospinal pathways at the level of spinal inhibitory neurons. The transcranial magnetic stimulation is a suitable method to assess the efficiency of drugs in patients with Parkinson's disease.