Introduction The aim of this study is to investigate the psychophysiological correlates of pleasant emotions with reference to the “bio- informational model of emotion” proposed by Lang. According to this model, emotional response is organized along the two main dimensions of valence and arousal, considered as primitive motivation parameters, involved in subcortical brain areas (1979,1984). Emotional sensations activate the Autonomic Nervous System, therefore we can measure emotional responses by means of the modifications occurring in that system. Heart rate variability and skin conductance are parameters not under conscience control, representing a pure visceral reaction. Heart rate is regulated both by sympathetic and parasympathetic branches of Autonomic Nervous System. A general deceleration in subjects looking at pleasant emotional stimuli compared to neutral ones (arousal) was observed. The present study examined the psychophysiological response to erotic visual stimuli, throught the registration of heart rate variability and skin conductance in male and female subjects, and in transessual FtM and MtF subjects. Materials and methods Forty-eight subjects were involved in the study: 12 male, 12 female, 12 transsexuals MtF and 12 transsexuals FtM. Some of the tranxessual subjects were in hormonal therapy at the time of the evaluaion. The mean (SD) age of the sample was 27.2 (1.6). The subject of the control group, 12 male and 12 female, did not suffer from Gender Identity Disorder or other psychiatric disorder and were matched for age and educational level to the transsexual group. Each subject was asked to watch 60 slides, selected from International Affective Picture System (IAPS), a set of normative emotional stimuli for experimental investigations of emotions (Lang, 1999). The slides set consisted of 20 negative slides, 20 positive slides and 20 neutral slides. All the pictures were in color and had been chosen for their ease of resolution and affective impact (valence, arousal and dominance). Each image was presented for a period of 6 seconds, followed by a blank screen for another six seconds. The slides were presented using a program run by Windows NT workstation. During the experimental session heart rate and skin conductance were recorded with a multichannel polygraph Galileo Sirius Star Ebineuro. In the present study we analysed the data relative to the 8 erotic slides (4 male and 4 female nudes), that were shown at the end of the pleasant set of slides. Results As far as the CONTROL GROUP is concerned, males and females showed opposite autonomic nervous system response while watching the nude slides (see figure 1-2). Specifically: - MALES evidenced a cardiac deceleration (higher arousal) and an increase in skin conductance watching female nudes. - FEMALES evidenced a cardiac deceleration (higher arousal) and an increase in skin conductance watching male nudes. Transsexualism and emotions: neurophysiologichal correlates to visual stimuli M. Molo, E. Cappai, L.Castelli, L. Rizzi, P.Perozzo, S. Vighetti, P. Cantafio CE.R.NE, Turin, Italy Contact: Similarly to the control group, comparing FtM vs MtF, TRANSSEXUAL evidenced an opposite psychophysiological pattern (see figures 3-4).  FtM subgroup highlights a psychophysiological pattern similar and substantially overlappable to the one showed by the males. This is true both for cardiac activity and for skin conductance.  On the contrary, MtF subjects revealed a similar autonomic nervous system response (cardiac activity and skin conductance) to the one observed in females. Discussion The most important finding of our study is the evidence of a similar autonomic nervous system response between male and FtM, and between female and MtF. Our results show a similar pattern of activation between transsexuals and people of the sex they would like to be. A cardiac deceleration (higher arousal) and a higher skin conductance occurred in the FtM transsexuals and in heterosexual men during the presentation of female nudes, suggesting a real sexual attraction toward women. The MtF transsexuals and heterosexual women showed a higher arousal looking at male nudes although their reactions were less manifest. Men and FtM transsexuals seem to be more able to express sexual attraction with involuntary reactions, while women and MtF seem to appear more inhibited viewing nudes. Transsexuals experience themselves as being of the opposite sex, despite having their biological characteristics. Overall our results confirm an emotional activation when looking at erotic pictures of the opposite sex: FtM, like males, react to female nudes, while MtF, like female, react to male nudes. In accordance to the sexual identity experienced by transsexual, the present study provides psychophysiological evidence of the attraction experienced by transsexual towards people of their own biological sex. References Bailey JM, Gaulin S, Agyei Y, Gladue BA. Effects of gender and sexual orientation on evolutionary relevant aspects of human mating psychology. J Person Social Psych 1994;66: Baldwin JR, Baldwin JI. Gender differences in sexual interest: Arch Sex Behav 1997;26: Greenwald Mk, Cook EW, Lang PJ., Affective judgement and psychophysiological response: dimensional covariation in the evaluation of pictorial stimuli, J Psychophysiology 1989, Janssen E, Carpenter D, Graham CA. Selecting films for sex research:gender differences in erotic film preference. Arch Sex Behav 2003;32(3): Lang, P.J., Bradley, M.M., Cuthbert, B.N. (1999) International affective picture system (IAPS): Instruction manual and affective ratings. Technical Report A-4, The Center For Research in Psychophysiology, University of Florida * * * * * * * p<.05 * FIG. 1 FIG. 2 FIG. 3 FIG. 4