Deep brain stimulation has been utilized to improve disease symptoms in patients with Parkinson's disease, dystonia, essential tremor, and other neuropsychiatric syndromes such as depression and obsessive compulsive disorder. Deep brain stimulation has also been observed to improve tremor for select patients with multiple sclerosis. During intraoperative stimulation in these multiple sclerosis patients, researchers have observed a wide spectrum of motor and sensory phenomena, but no stimulation-induced emotional responses have been reported. We detailed intraoperative smiling associated with stimulation of the ventralis oralis anterior/ventralis oralis posterior border region of the left thalamus. A single patient with medication-resistant multiple sclerosis tremor experienced smiling, laughing, and subjective euphoria during intraoperative stimulation of the left thalamus. Specifically, during intraoperative stimulation of the left thalamic ventralis oralis anterior border, the patient developed a contralateral smile which progressed to a bilateral smile and was accompanied by a feeling of subjective happiness. The smile habituated in approximately 60 seconds and it was reproducible on a repeat stimulation. The patient could subjectively feel the facial movement, and, at higher voltages, the movement was described as a pulling sensation. Stimulation of the anterior ventralis oralis anterior border of the left thalamus in an multiple sclerosis patient produced a unilateral smile that rapidly developed into a bilateral smile accompanied by euphoria. There were presumed capsular side effects at higher voltages. The exact mechanism by which stimulation of the thalamus produced a smile and mood elevation is unknown, but we speculate that the smile could be induced by stimulation of corticobulbar fibers arising from the caudal cingulate motor area connecting the contralateral facial nerve nucleus.
Keywords: Complication; Deep brain stimulation; Laugh; Multiple sclerosis tremor; Smile; Thalamus; Ventralis oralis anterior (VOA); Ventralis oralis posterior (VOP).