Laughter and electroencephalographic activity

information processing. Waveform components within an event-related brain potential (ERP) triggered by a stimulus are indicators of subsequent perceptual and cognitive processing. A positive wave at about 300 milliseconds (P300) following the presentation of a stimulus indicates the activity of categorization while a negative wave at about 400 milliseconds (N400) corresponds with a disruption and possible extension of the categorization process. This ''incongruity'' wave prompted speculation that similar neural activity might occur in humor. In a pilot study one participant showed clear evidence of P300 and N400 over the whole cortex when responding to humorous stimuli. A subsequent experiment attempted to manipulate the mood of additional subjects prior to the presentation of the humorous stimuli. ERP activity was used to compare jokes that did or did not elicit laughter. Although the mood manipulation resulted in only weak and inconsistent subjective and behavioral changes, there was some evidence of cortical changes. More significantly, jokes that did not produce laughter showed no evidence of the N400 while those that elicited laughter did shaw this electrical pattern of disrupted categorization.