Repetitive Transcranial Magnetic Stimulation (rTMS) for the Treatment of Apathy in Parkinson's Disease

Apathy is a syndrome characterized by a primary lack of motivation and it manifests in three domains: behavioral (lack of effort and productivity, dependence on others for structuring daily activities), cognitive (loss of interest in new experiences, lack of concern for one's problems) and affective (flattened affect and lack of response to positive or negative events). Apathy has been consistently attributed to functional disturbance of neural systems involving mesial frontal and the anterior cingulate cortex (ACC), an area with reciprocal connections with limbic, frontal cortices and the basal ganglia. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive tool used to manipulate activity in specific brain neural circuits through the skull and, in turn, induce short-term (milliseconds) and long-term (minutes to hours) changes in behavior. The duration of effect depends on the stimulation mode. Several studies have now demonstrated that rTMS may facilitate or modulate behavior beyond the actual stimulation. rTMS of the mid-dorsolateral frontal cortex (MDLFC) has been used to treat depression presumably because of its modulatory effect on the fronto-cingulate system (MDLFC and the ACC circuitry). Studies have shown that rTMS of the left MDLFC modulates the blood flow response in the ACC. We therefore hypothesize that high-frequency rTMS of the left MDLFC will also improve apathy in PD.