Despite widely accepted biological theories, the etiopathogenesis of the gender dysphoria [1] remains largely unclear.Several studies have shown the existence of some gender-related cerebral areas. Indeed, various areas belonging to the limbic system such as stria terminalis, preoptic nucleus, and amygdala are characterized by a sexual dimorphism both in macroscopic and microscopic structures [2,3]. Men and women are different in processing cognitive and emotional stimuli [4].A common neurophysiologic approach to assess cognitive functions is based on event-related potential (ERP) analysis, especially on the evoked component called P300. The P300 wave is a centro-parietal positive deflection in human ERP, which occurs about 300 milliseconds after stimuli's appearance and it is known as the "cognitive wave" [5].Few scholars have studied male to female (MTF) transsexuals through neurophysiologic studies.We designed a prospective case-control study. Fifteen MTF transsexuals, aged average 35 years and an age matched control group of 20 healthy right-handed heterosexual volunteers (10 males and 10 females) underwent an emotional ERP test. The cognitive-emotional ERPs were achieved while the subjects were watching slides extracted from the International Affective Picture System (IAPS). Sixty pictures, divided in two series with positive/ neutral and negativeeutral valences were shown randomly to the subjects. The area below the P300 wave, its amplitude and latency were compared before and after sex reassignment surgery (SRS) in transsexuals and with control groups.
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