A prospective study of the effects of anterior temporal lobectomy on emotion recognition and theory of mind.

Nineteen patients evaluated facial emotional expressions and performed 'theory of mind' reasoning tasks before and after a temporal lobectomy for medically intractable epilepsy, and results were compared with the performance of 19 healthy controls. Following operation, which in all cases resulted in excision of the entire amygdala, there was no change in the ability to reason about the mental states of others, in line with the suggestion that the anterior temporal lobe is not necessary for theory of mind reasoning. However, following a left anterior temporal lobectomy, patients evaluated fearful facial expressions in a more normative manner. This may reflect the excision of a 'hyper-excitable' amygdala which pre-operatively misinterprets fearful expressions as containing blends of other emotions. Alternatively the results may represent an improvement in function of the right amygdala following the excision of a noxious inhibitory epileptogenic focus on the left. The finding complements earlier demonstrations that damage to the right amygdala is associated with impaired processing of fear; amelioration of right amygdala function may conversely be associated with an improvement.