Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Brain activation and sexual arousal

 

Brain, Vol. 125, No. 5, 1014-1023, May 2002

Brain activation and sexual arousal in healthy, heterosexual males

Bruce A. Arnow¹, John E. Desmond¹, Linda L. Banner¹, Gary H. Glover¹, Ari Solomon¹, Mary Lake Polan¹, Tom F. Lue¹ and Scott W. Atlas¹

Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, Calif., USA

(paraphrase)

Despite the brain’s central role in sexual function, little is known about relationships between brain activation and sexual response. In this study, we employed functional MRI (fMRI) to examine relationships between brain activation and sexual arousal in a group of young, healthy, heterosexual males. Each subject was exposed to two sequences of video material consisting of explicitly erotic (E), relaxing (R) and sports (S) segments in an unpredictable order. Data on penile turgidity was collected using a custom-built pneumatic pressure cuff. Both traditional block analyses using contrasts between sexually arousing and non-arousing video clips and a regression using penile turgidity as the covariate of interest were performed. In both types of analyses, contrast images were computed for each subject and these images were subsequently used in a random effects analysis. Strong activations specifically associated with penile turgidity were observed in the right subinsular region including the claustrum, left caudate and putamen, right middle occipital/ middle temporal gyri, bilateral cingulate gyrus and right sensorimotor and pre-motor regions. Smaller, but significant activation was observed in the right hypothalamus. Our study demonstrates the feasibility of examining brain activation/sexual response relationships in an fMRI environment and reveals a number of brain structures whose activation is time-locked to sexual arousal.

The large and significant activation in the right insula/subinsular region (including the claustrum) is strikingly similar to findings reported in PET studies of male sexual arousal. While the insula has been linked to motor, vestibular and language functions, it also lies in close proximity to the secondary somatosensory cortex, and both projects to and receives projections from the latter. Evidence from a number of studies suggests that the insula is involved in visceral sensory processing including studies of taste and oesophageal stimulation. In addition, evidence including increased rCBF in the insula following vibrotactile stimulation has led to the conclusion that the insula functions as a somatosensory processing area. Thus, activation observed in the insula in the present study may reflect somatosensory processing and recognition of erection.

Dopamine is projected to both the hypothalamus and the striatum from the incertohypothalamic area and the substantia nigra, respectively. Evidence that dopamine facilitates male sexual behavior is substantial. For instance, dopamine agonists such as apomorphine have been shown to induce erection in men with both normal and impaired erectile function, while antipsychotics which decrease dopaminergic activity are associated with erectile impairment. Another dopamine agonist, L-dopa, a medication for Parkinson’s disease which itself is associated with 80–90% dopamine reductions in the striatum, has been shown to produce erection in men. While there are several dopamine systems in the central nervous system, animal studies have linked both the nigrostriatal and the incertohypothalamic dopamine systems to sexual behavior.

Activation in the anterior cingulate cortex, specifically BA 24 and BA 32, was also associated with tumescence. The anterior cingulate is known to be linked to attentional processes. Researchers have suggested that BA 24 and BA 32 may guide responsiveness to new environmental stimuli. Abnormalities in anterior cingulate function have been reported in patients with obsessive–compulsive disorder, autism,  and autism spectrum disorders, all of which are characterized by repetitive behaviour and difficulties shifting attention. However, contributions of the anterior cingulate to sexual response may also be more direct. BA 24 and BA 32 are involved in modulating autonomic and endocrine functions including gonadal and adrenal secretion. Electrical stimulation to BA 24 has been shown to bring about erection in monkeys.

Activation during erection was also observed in the right middle temporal and middle occipital gyri (BA 37/19). Considerable evidence suggests that visual processing is a major function in this area. In a PET study focused on novel and familiar word and face stimuli, significant right hemisphere activation was reported in areas 37 and 19 in the novel and familiar face conditions, but not in either word condition. Other data suggest that BA 37/19 may be specifically involved in processing novel visual stimuli. In an fMRI investigation comparing face perception and memory using a repeated face, unrepeated novel faces, nonsense scrambled faces and a blank screen, areas 37 and 19 were significantly activated during the novel face condition but not during the comparison conditions. Similar to face processing, the visual focus of our participants is likely to have involved considerable feature abstraction.

The present study specifically investigated the neural correlates of sexual arousal in young healthy males. Of significant interest for future studies is how these activations might change as a function of age, and how male and female brain activations might differ. With respect to such differences, a recent 1.5 T fMRI study of six females reported activation sites in areas of the thalamus, amygdala, anterior temporal cortex, fusiform gyrus, inferior frontal gyrus and posterior temporal regions^. These activations do not overlap with the large insular/sub-insular, cingulate and basal ganglia activations observed in the present study. Further studies will be needed to determine if such discrepancies reflect gender or paradigm differences in sexual arousal related brain activation.

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Viewing Erotic Films

Appetites and desires aroused by viewing erotic films -- cingulate cortex and insular cortex are very much engaged so that we can feel the excitement.  Regions such as the orbitofrontal cortices and the striataum and are also engaged and whipping up the excitement.  Remarkable difference in the hypothalamus engagement -- males engage the hypothalamus in significantly; females do not. (Damasio; Looking for Spinoza, 104)