Neuropsychiatric effects of subthalamic neurostimulation in Parkinson disease

Neurostimulation of the subthalamic nucleus (STN) is an established treatment for motor symptoms in advanced Parkinson disease (PD), although concerns exist regarding the safety of this therapy in terms of cognitive and psychiatric adverse effects. The basal ganglia are considered to be part of distributed cortico-subcortical networks that are involved in the selection, facilitation and inhibition of movements, emotions, behaviors and thoughts. The STN has a central role in these networks, probably providing a global 'no-go' signal. The behavioral and cognitive effects observed following STN high-frequency stimulation (HFS) probably reflect the intrinsic role of this nucleus in nonmotor functional domains. Nevertheless, postoperative behavioral changes are seldom caused by such stimulation alone. PD is a progressive neurodegenerative disorder with motor, cognitive, behavioral and autonomic symptoms. The pattern of neurodegeneration and expression of these symptoms are highly variable across individuals. The preoperative neuropsychiatric state can be further complicated by sensitization phenomena resulting from long-term dopaminergic treatment, which include impulse control disorders, punding, and addictive behaviors (dopamine dysregulation syndrome). Finally, personality traits, the social environment, culture and learned behaviors might be important determinants explaining why behavioral symptoms differ between patients after surgery. Here, we summarize the neuropsychiatric changes observed after STN HFS and try to disentangle their various etiologies.