Human brain activation during sexual stimulation of the penis.

Penile sensory information is essential for reproduction, but almost nothing is known about how sexually salient inputs from the penis are processed in the brain. We used positron emission tomography to measure regional cerebral blood flow (rCBF) during various stages of male sexual performance. Compared to a passive resting condition (without penile erection), sexual stimulation of the penis increased rCBF in an area of the right hemisphere encompassing the posterior insula and adjacent posterior part of the secondary somatosensory cortex (SII) and decreased rCBF in the right amygdala. No activation was observed in either the thalamus, genital part of primary somatosensory cortex (SI), or hypothalamus. Based on these results we put forward the concept that during sexual performance the salience of the stimulus, represented by activation of the insula and SII, is of greater significance than the exact location of the stimulus, encoded in SI. The absence of activation in the hypothalamus indicates that this region is more important for the onset of sexual arousal than for the resulting sexual performance. Deactivation of the amygdala during sexual stimulation of the penis corresponds with a decrease of vigilance during sexual performance. (c) 2005 Wiley-Liss, Inc.