Sex on the Spectrum

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition with the core symptoms of deficits in social communication and interaction, and the presence of restricted repetitive behaviours. Sexual interactions are one of the most complex and demanding of all human social behaviours. So how does ASD impact sexual life?

Some studies of this issue have found differences in sexual knowledge, experiences, attitudes and behaviours between people with ASD and ‘neurotypicals’ (those without the condition), while others have found no differences at all. This inconsistency is not surprising given the heterogeneous nature of ASD, and the methodological variations between studies.

Research has found that people with ASD do seek out sexual relationships and experience the full range of human sexual activities and behaviours. In some cases, however, the core symptoms of the condition, combined with limited sexual knowledge and experience, can play a role in the development of challenging sexual behaviours, such as hypersexuality, paraphilic disorders and, in rare cases, even sexual offending.

Hypersexuality, and paraphilic fantasies and behaviours, have been found to be more common in adult males with ASD than in neurotypical people; some researchers have hypothesised that the restricted interests and repetitive behaviours commonly seen in ASD may transform into sexualised behaviours in adulthood. Furthermore, a sensitivity to sensory stimuli, in particular touch, can lead to an over- or under-reaction to sexual stimulation.

Excessive masturbation is relatively common in males with ASD. For example, in one case study it was reported that a 17-year-old man with a diagnosis of Asperger’s syndrome (now called high functioning ASD) had intrusive sexual thoughts and urges, and was masturbating 25 to 30 times a day.

It is unclear whether this excessive behaviour represented a repetitive behaviour, was part of an obsessive-compulsive disorder (common in people with ASD), was the result of sensory hyposensitivity, or was the only means of him being sexually active due to limited social skills. Public masturbation was the most common type of inappropriate sexual behaviour reported by carers or parents of adolescents and adults with ASD.

Why are these sexual behaviours found more frequently in males with ASD? First, there are more males than females diagnosed as on the spectrum, at a ratio of somewhere around 3:1 or 4:1, and much of the research about sex on the spectrum has focused on men.

Interestingly, a study published in 2017 by Daniel Schöttle and colleagues that directly compared hypersexuality in people with ASD and neurotypicals found that there were no differences between females on the spectrum and those who were neurotypical. The authors of this study argued that this gender difference was due to the observation that females with ASD ‘seem to be better socially adapted and usually show less pronounced ASD symptomatology’.

But did the study find that rates of hypersexuality in males with ASD were higher than in the general population? Yes, it did. Previous studies of the prevalence of hypersexuality in healthy males give estimates of 3–12 per cent, and in the males with ASD in the study, the prevalence of hypersexuality was 30 per cent.

This same study also looked at rates of paraphilias in people with ASD. The most common paraphilias reported by males with ASD were voyeuristic fantasies (39%) and behaviours (28%), while in the neurotypical group such fantasies and behaviours were reported in 10% and 3% of subjects respectively.

Masochistic (sexual arousal from suffering physical pain or humiliation) and sadistic (sexual arousal from inflicting physical or psychological pain on a sexual partner) fantasies and behaviours were also reported more often by males with ASD than those without. It is thought that this may be due to a high level of sensory hyposensitivity in people with ASD – that is, lack of sensitivity – and the corresponding need for higher levels of stimulation to become sexually aroused. Furthermore, a heightened sex drive may mean that people with ASD are more likely to act out their sexual interests and to seek novel sexual activities.

Is there anything different about the parts of the brain that control sex in people with ASD that might help explain the higher rates of some sexual behaviours? ASD is neurodevelopmental in origin, meaning that the brain changes start in utero and continue over time. There are enormous variations in how ASD affects people, so understanding and describing the neurobiological mechanisms underlying ASD is complex. Nevertheless, based on numerous neuroimaging studies that have compared the brains of people with ASD and neurotypicals, there is a consensus that anatomical structure, functioning and connectivity do differ between the two groups.

In the largest neuroimaging study to date of people with ASD – 1500 people were studied, ranging in age from 2 to 64 years – a group of international experts found that compared with neurotypicals, people with ASD had a larger total brain volume and cortical thickness, and smaller volumes of specific brain structures including the amygdala and parts of the basal ganglia (nucleus accumbens, putamen). The ASD group also showed increased thickness of the frontal cortex, and decreased thickness of the temporal cortex. The basal ganglia, frontal and temporal brain regions all play a role in the sexual neural network.

From a broader perspective, these brain regions are also part of what has been termed the ‘social and emotional brain’, a larger network of brain structures that are involved in processing social and emotional information, such as empathy, face processing and self-referential processing.

As psychiatry professor Christine Ecker highlights in her overview of these neuroimaging findings, it is important to note that ‘the neuroanatomical differences are neither unique to, nor causal for ASD’.

In regard to the differences in sexual behaviour between people with ASD and neurotypicals, there has been no study to date that has investigated whether differences exist in the brains of those with ASD who have paraphilias or hypersexuality as compared to those with ASD who do not have these specific sexual behaviours.

So although we know that, overall, it appears that people with ASD do have brain differences in regions that are part of the sexual neural network, not all people with ASD experience sexual changes, and we don’t know if there is something unique about the brains of those people who do. This is a question for future research.

This is an adapted excerpt from 'Sex in the Brain: How your brain controls your sex life' (NewSouth Publishing, 2019; Columbia University Press, 2020)