The Civic Platform - A Political Journal of Ideas and Analysis

Neuroimage. 2006 Nov 15;33(3):825- 33. Epub 2006 Sep 18.

A functional endophenotype for sexual orientation in humans.

Sexually arousing visual stimuli activate the human reward system and
trigger sexual behavior. Here we performed event-related fMRI during
visual processing of sexual core stimuli to pinpoint a neuronal
correlate of sexual preference in humans. To dissociate gender of the
stimulus from sexual preference, we studied male and female
heterosexual and homosexual volunteers while they viewed sexual and
nonsexual control stimuli. In contrast to previous work, we used core
single-sex stimuli displaying male and female sexually aroused
genitals. Since stimuli lacked any additional contextual information,
they evoked no activity related to neuronal processing of faces,
gestures or social interactions. Our prediction was that the sexual
preference of the observer determines the neuronal responsiveness to
pure male or female sexual stimuli in the human reward and motor
system. Consistent with our prediction, the ventral striatum and the
centromedian thalamus, showed a stronger neuronal response to
preferred relative to non-preferred stimuli. Likewise, the ventral
premotor cortex which is a key structure for imitative (mirror
neurons) and tool-related (canonical neurons) actions showed a
bilateral sexual preference-specific activation, suggesting that
viewing sexually aroused genitals of the preferred sex triggers action
representations of sexual behavior. The neuronal response of the
ventral striatum, centromedian thalamus and ventral premotor cortex to
preferred sexual stimuli was consistent across all groups. We propose
that this invariant response pattern in core regions of the human
reward and motor system represents a functional endophenotype for
sexual orientation independent of the gender of the observer and
gender of the stimulus.
PMID: 16979350

http://www.ncbi. nlm.nih.gov/ entrez/query. fcgi?db=pubmed& list_uids= 16979350& cmd=Retrieve& indexed=google