Abstracts

Rationale: Much of the knowledge on the functional anatomy of the brain is obtained from electrical cortical stimulation studies. There are several reports of mirth and laughter triggered by stimulation of several locations in the temporal and frontal cortices. In few other reports, laughter without mirth occurred following stimulation of right mesial frontal region. This led to the impression that mirth is predominantly related to the dominant hemisphere. Methods: We present a 37-year old right-handed male who started having seizures at the age of 6 years. He does not have etiological risk factors for epilepsy. He suffered nocturnal seizures occurring on a daily basis, consisting of brief irregular hypermotor movements. Scalp EEG was not localizing or lateralizing. MRI was nonlesional. PET was unremarkable. Ictal SPECT demonstarted left anterior frontal hyperperfusion. Neuropsychological evaluation suggested limitations with visual processing and executive functioning. The patient underwent implantation of subdural strip electrodes covering lateral and mesial frontal and parietal regions. The earliest electrographic ictal changes were seen in bilateral mesial parietal regions. Cortical stimulation was performed using biphasic stimulation with pulses of 0.3 ms at 50 Hz in trains lasting 5 seconds, and a stimulation intensity of 1-15 mA. Results: The patient experienced a mirthful feeling associated with laughter following stimulation of the right mesial frontal region anterior to the supplementary sensorimotor motor area (SSMA). This was first elicited at a stimulation intensity of 7.0 mA and was consistently reproducible. The patient laughed and reported a complex emotion of amusement. He described feeling as if he were making fun of others or that he wanted to tell "the best joke this summer." Conclusions: In previously published reports, laughter with mirth was triggered by stimulation of the electrodes in the left/dominant temporal or frontal regions (basal temporal area, left inferior frontal gyrus, and left mesial frontal region rostral to the SSMA). Mirth was absent in cases where laughter was triggered with stimulation of the right cingulate or medial frontal region. Our case demonstrates that mirth is not always "lateralized" to the dominant hemisphere as may be suggested by previous reports. The area where stimulation induced mirth in our patient could be homologus to that described by Krolak-Salmon (2006) in the left pre-SSMA. Funding: NA