Robert Mapplethorpe - Untitled (Self Portrait)
The previous post (Erotic or Disgusting?) covered a functional MRI experiment on the neural responses to erotic films in heterosexual and homosexual males (Zhang et al., 2010). Specifically, the study examined sexual arousal and disgust while the participants viewed various types of porn. Neuroimaging results were reported only for the stimuli deemed distasteful by each group, wherein the left ventromedial prefrontal cortex was more active for gay men, and the left cuneus [visual cortex] was more active for straight men. It was unclear why this particular outcome was obtained. Other problems with the paper included the comparison condition (passive rest, rather than viewing neutral film clips) and the analysis strategy.
An earlier study, however, took a more comprehensive look at arousal and disgust in a different sexual minority group: those with sadomasochistic preferences, who were compared to those without (Stark et al., 2005). Here, the stimuli were pictures from four categories: neutral, disgust-inducing, erotic, and sadomasochistic:
The erotic pictures included either pictures of single naked subjects or pictures of couples in an intimate situation. The pictures with sadomasochistic content either had a submission/dominance theme (e.g. a naked man pulling a coach with a dressed woman), or showed sadomasochistic techniques (e.g. hurting someone with hot wax, pictures of bound subjects). The scenes depicted single subjects (male and female), couples, and groups of subjects.The disgust-inducing pictures showed a broad range of different disgust elicitors: unusual food (e.g. man eating a grasshopper, man biting into a monkey head), disgusting animals (e.g. snails, maggots), poor hygiene (e.g. dirty toilet, garbage piles, and body products (e.g. excrements, vomit). Neutral pictures showed household articles, geometric figures, and nature scenes.This allowed within-subject and between-subject approaches in the same experiment. Presumably, rotting garbage would be disgusting to everyone, while the groups would differ in their reactions to images with erotic or sadomasochistic content.
Participants were 24 adults, 12 of whom identified as having sadomasochistic sexual preferences (SM)1 and 12 without sadomasochistic preferences (non-SM). Each group was comprised of 6 men and 6 women. Subjects were initially classified by asking, “Are you interested in sadomasochistic sexual activities?” This was followed by an 8 item questionnaire asking about sexual orientation, identity, and experiences, with each item rated on a 5-point scale (e.g., “I describe myself as a sadomasochist”, “I describe myself as sadistic/dominant”, etc.).
All pictures were rated in advance by separate groups of SM and non-SM participants on the dimensions of disgust and sexual arousal using 9-point visual analog scales, and on valence, arousal, and dominance using the self-assessment manikin (also on a scale from 1 to 9). The scanned subjects also rated the pictures after the fMRI experiment was over. The emotional ratings for neutral and disgust-inducing stimuli did not differ between the two groups. As expected, however, ratings for the other two stimulus classes were divergent:
The erotic pictures revealed more positive affect, more arousal, and more sexual arousal for the nonSM group in comparison to the SM group. SM subjects indicated to have felt more positive, more dominant, less disgusted, and more sexually aroused during the presentation of the pictures with sadomasochistic content than the nonSM subjects.Statistically speaking, emotion ratings for the disgust-inducing and sadomasochistic images did not differ in the non-SM group.2 On the other hand, ratings for the sadomasochistic pictures in the SM participants were similar to those for erotic pictures in the non-SM group. These findings were important for the between-subjects comparison of disgust and sexual arousal.
During the fMRI experiment, each category of pictures was presented in separate blocks. Subjects were instructed to “let the pictures affect you”. For data analysis purposes, a number of different comparisons were performed:
Several T-contrasts were calculated for each subject: the emotional conditions versus the neutral condition (Disgust <> Neutral, Erotic <> Neutral, Sm <> Neutral), and for the positive emotion versus negative emotion (Erotic <> Disgust, Sm <> Disgust, Sm <> Erotic). For a random effect analysis the individual contrast images (first level) were used in a second level analysis.As you can imagine, the amount of data reported in this paper is voluminous. Brain regions of interest (ROIs) were selected from the meta-analysis of Phan et al. (2002) on neuroimaging studies of emotion. Exploratory analyses were performed as well.
The Erotic or Disgusting? Pleasure or Pain? series will conclude next time with the functional neuroanatomy associated with states of disgust and sexual arousal in those with vanilla and BDSM preferences.
1 Specific orientations were as follows:
In the SM group three subjects reported a bisexual orientation (two male, one female). Furthermore, the SM group could be separated into eight masochists (four female), one sadist (female) and three switchers (one female).2 Numerically speaking, however, disgust ratings were higher for the former than for the latter (6.67 vs. 4.25).
Phan KL, Wager T, Taylor SF, Liberzon I. (2002). Functional neuroanatomy of emotion: a meta-analysis of emotion activation studies in PET and fMRI. Neuroimage 16:331-48.
STARK, R., SCHIENLE, A., GIROD, C., WALTER, B., KIRSCH, P., BLECKER, C., OTT, U., SCHAFER, A., SAMMER, G., & ZIMMERMANN, M. (2005). Erotic and disgust-inducing pictures—Differences in the hemodynamic responses of the brain. Biological Psychology, 70 (1), 19-29 DOI: 10.1016/j.biopsycho.2004.11.014
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