ORIGINAL RESEARCH-ANATOMY/PHYSIOLOGYA Quantitative Meta‐Analysis on Cue‐Induced Male Sexual Arousal
Introduction
Sexual behavior is one of the most important goal‐directed behaviors that are associated with the survival of the species. According to sociobiology (e.g. [1]) the pressure of natural selection has supported the emergence of brain systems that promote sexual behaviors that increase fitness, namely the aptitude to transmit one's genes. Especially during the initial approach phase processing of external sexual stimuli is of utmost importance. In mammals, it has been shown that sexual behavior in male mammals is promoted by odors that indicate the reproductive state of females [2]. In animals, the role played by subcortical structures, particularly the amygdala and hypothalamus, in sexual behavior has been well documented [3]. However, it has been remarked that human sexual behavior comprises unique characteristics that distinguish it from the homologous behavior in other species, such as the cognitive aspects of sexuality [4]. With the aim of exploring the neural correlates of sexual arousal as elicited by external sexual stimuli consisting of still images or videos, also referred to as “cues,” several neuroimaging studies have investigated the cerebral activation during erotic visual stimulation. Many of the studies using cue‐reactivity paradigms comprising sexual stimuli implicitly assume that the experimental setup elicits sexual arousal. Although there is little consensus on the concept of sexual arousal we use this term to describe an appetitive motivational state of sexual excitement or desire comprising a cognitive, emotional, motivational, and physiological component. In line with the assumption that sexual stimuli elicit sexual arousal, we aimed at testing whether brain areas that consistently show increased activity in response to sexual cues overlap with brain areas that are consistently correlated with a physiological measure of sexual arousal, namely penile turgidity. Studies using cue‐reactivity paradigms have highlighted a complex neural circuitry involved in the human sexual response (e.g. 5, 6, 7, 8). In order to provide a systematic assessment of brain regions involved in cue‐induced sexual arousal, we performed a quantitative meta‐analysis. We included functional magnetic resonance imaging (fMRI) studies that presented erotic visual stimuli to male subjects and compared the associated brain activity with the brain activity elicited by neutral visual stimuli in order to assess the correspondence of neural activation across multiple neuroimaging studies. We present a meta‐analysis on studies including male subjects with heterosexual orientation. Moreover, to relate brain activation during the observation of sexual cues with a physiological marker of sexual arousal, we conducted a second meta‐analysis on whole brain correlations with penile turgidity. By means of the activation likelihood estimation (ALE) approach 9, 10, 11 we explored statistically significant concordance of activated voxels across numerous studies while controlling for chance clustering. ALE tests for statistically reliable clustering of activations in standardized locations avoiding spatial distinction errors and problematic incongruence of labeling across studies that could have befallen narrative‐based reviews and tabular meta‐analytic approaches on cue‐induced sexual arousal that have been published previously.
Section snippets
Study Selection
Studies were selected using a systematic search of peer‐reviewed articles published in English until August 2010. We used two separate databases (Pubmed, ISI Web of Knowledge) with the keywords “neuroimaging” or “fMRI” and “sexual arousal” or “sexual cues.” The reference lists of these selected papers were searched for additional studies that fit these criteria. From the resulting articles, we selected those that presented visual cues with sexual content and compared these with neutral
Results
The quantitative meta‐analysis on cue‐induced male sexual arousal in heterosexual subjects revealed significant convergence in hypothalamus extending into thalamus, bilateral amygdala, anterior cingulate gyrus (ACC; extending into corpus callosum), bilateral fusiform gyrus, bilateral anterior insula, right mid‐posterior insula, bilateral precentral gyrus, bilateral middle occipital gyrus, and additionally the right inferior and superior parietal cortex (Figure 1 in red). Coordinates of
Discussion
Within the scope of the present quantitative meta‐analyses, we assessed the strength of evidence for the presence of a core network of brain regions involved in the observation of sexual stimuli (including still pictures and videos) and the resulting cue‐induced male sexual arousal. In the first analysis including studies on male heterosexuals, we identified the importance of the hypothalamus, thalamus, left amygdala, ACC, left anterior insula, bilateral fusiform gyrus, left precentral gyrus,
Acknowledgment
The first author is a Postdoctoral Fellow of the Research Foundation Flanders (FWO).
Conflict of Interest
None.
Category 1
- (a)
Conception and Design
Simone Kühn; Jürgen Gallinat
- (b)
Acquisition of Data
Not valid
- (c)
Analysis and Interpretation of Data
Simone Kühn; Jürgen Gallinat
Category 2
- (a)
Drafting the Article
Simone Kühn; Jürgen Gallinat
- (b)
Revising It for Intellectual Content
Simone Kühn; Jürgen Gallinat
Category 3
- (a)
Final Approval of the Completed Article
Simone Kühn; Jürgen Gallinat
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