The use of non-invasive brain stimulation as a potential treatment for sexual disorders

By Geraldine Rodríguez Nieto, Maastricht University, geraldine.rodriguez@maastrichtuniversity.nl

For Citation: SITE4Society Brief No.18-2019
Related to SDG Goals and Indian National Programmes: SDG 3 good health and well-being, SDG 5 gender equality
Country Focus: Unrestrictive / Any region with access to transcranial magnetic stimulation.
SITE Focus: Science, Innovation, Engagement
Sub-disciplines Cognitive Neuroscience.
Based on: Rodríguez-Nieto, G., Sack, A.T., Dewitte, M., & Schuhmann, T. (2018). Inhibit my disinhibition: The role of the inferior frontal cortex in Sexual Inhibition and the modulatory influence of sexual excitation proneness. Frontiers in Human Neuroscience. doi:  [10.3389/fnhum.2018.00300]

 

Research Output Description

Context: The regulation of sexual desires and behaviour is essential to maintain health and social harmony. The impairment of the ability to regulate sexual behaviour can result in a wide spectrum of undesired consequences including sexual risk behaviour and sexual offense. Sexual risk behaviour can lead to undesired pregnancy and the contagion of sexually transmitted diseases. On the other hand, sexual offense consequences include different long-term mental health problems to the victim, such as post-traumatic stress or addiction proneness, among others.

The prevalence of sexual offenses and child abuse is high in both developed and developing countries. Although the prevalence numbers are difficult to estimate due to the fact that sexual offenses are not always reported or registered, in the United States for instance, it has been estimated that child abuse make up 500,000 cases per year (Fuller, 1989). It has also been suggested that increased access to sexual material can make vulnerable individuals prone to escalate their behaviour (e.g. from watching illegal pornography to risky real-life sexual behaviour) which may pose a threat for the integrity of other individuals, in particular females and children (Young, 2008).

For this reason, the scientific study of the etiology or causes of the incapability to control sexual urges is fundamental in order to prevent risky and antisocial sexual practices. So far, the treatments for individuals seeking help or convicted sexual offenders include psychotherapy and pharmaceutical intervention. The pharmaceutical intervention poses the problem of presenting side effects (e.g. nausea, mood changes and bone reduction) which may lead to a low treatment adherence. Further, both psychotherapy and pharmaceutical intervention are efficient only in some cases.

Therefore we aimed to study the effect of non-invasive brain stimulation on the performance of basic sexual inhibitory processes, in order to evaluate whether this technique can be eventually used as a treatment in individuals on risk of offending.

Research Questions: Is it possible to modulate sexual inhibition through non-invasive brain stimulation?

Motivation for Research Questions: Since the thoughts and behaviour of individuals are the output of brain functioning, it is theoretically possible to influence cognition and behaviour by the manipulation of neural mechanisms. However, as the brain is a complex network of different processing nodes, a careful and deep understanding of the neural mechanisms underlying sexual inhibition is necessary to design protocols aimed at treating sexual disorders.

The successful treatment of sexual disorders that comprise the ability to inhibit sexual behaviour may prevent the abuse and offense of vulnerable individuals.

Data and Methodology Used: One way to modulate brain activity, and therefore cognitive processes and behaviour, is through non-invasive brain stimulation techniques. One of these techniques is Transcranial Magnetic Stimulation or TMS (Fig. 1). Used in clinical contexts to treat depression, this technique allows to modulate the brain activity through the use of magnetic fields in a non-invasive manner (the magnetic field is sent through a coil located over the head of the individual without the need of surgery).               Fig 1. The transcranial magnetic stimulation technique works through the magnetic fields emitted by a coil to modulate specific brain regions.

Our goal was to investigate whether it would be possible to modulate sexual inhibition through TMS. For this purpose, a final sample of twenty two healthy young males performed tasks on the computer designed to tackle cognitive sexual inhibition and motivational sexual inhibition.

  • Cognitive sexual inhibition relates to the control over sexual thoughts; and,
  • Motivational sexual inhibition refers to the control of reward driven actions.

 

Participants underwent three sessions. In each session, prior to the execution of the tasks, participants underwent one of the three stimulation treatments. Each treatment consisted of 40 seconds of transcranial magnetic stimulation. During one of the experimental sessions we stimulated the inferior frontal gyrus, a brain region previously associated with general inhibitory processes. And in the other experimental session we stimulated the precuneus, as an experimental control area, which had shown to be active during sexual non-inhibitory processing. In the control session participants were stimulated with a placebo coil, this is with no real TMS.

After stimulation, participants were instructed to perform tasks in which they had to inhibit the virtual approach towards sexual stimuli (motivational sexual inhibition, Fig 2) or ignore such stimuli in an attention paradigm (cognitive sexual inhibition, Fig 3). The execution of the tasks took approximately 30 minutes.

Fig 2. In this task participants were instructed to either approach (block A) or avoid (block B) sexual photographs and to do the opposite with non-sexual photographs. Participants could approach and avoid images with a joystick, which being pulled cause an image enlargement and while being pushed caused a halving. We compared the time that participants took to approach and avoid sexual stimuli, and in turn with those times from non-sexual stimuli.

 

Fig 3. In each trial of this task participants were presented with two simultaneous photographs, one black-framed and one grey-framed, and participants were instructed to indicate through button pressing whether the black-framed image was sexual or non-sexual. Inhibition is measured through the negative priming effect, which is defined by a delay to respond in certain trial (probe trial) to the kind of image that was ignored (grey framed) in the immediate previous trial (prime trial). Thus, the inhibition is measured in priming trials in comparison to non-priming trials, and in addition we compared the sexual priming trials against non-sexual priming trials.

At the end of the last session individuals filled in questionnaires to report the degree to which they are easily sexually aroused and to what extent they are able to inhibit their sexual desire under inappropriate contexts (max. 30 minutes).These questionnaires aim to measure these features as traits, this is, as something that is stable across time.

We performed linear regressions in order to investigate whether the stimulation treatment (independent variables) had an effect over cognitive sexual inhibition and motivational sexual inhibition (dependent variables). We further performed these analyses controlling for sexual excitation scores (the degree to which participants reported being easily sexually aroused).

Main findings:

  1. The use of Transcranial Magnetic Stimulation or TMS (non-invasive brain stimulation) over the inferior frontal gyrus improved the performance of cognitive sexual inhibition in individuals who reported being easily sexually aroused (F(2,40) = 6.24, p = 0.004) (Fig. 4).
  2. However, the regressions could not confirm any definite impact of the TMS intervention on motivational sexual inhibition in both the sites (F(2,42)= 1.53, p = 0.22). This could be due to the large dispersion in the data (Table 1). Therefore, it remains to be investigated whether the used protocol can be used as a treatment of individuals with sexual control impairments.

 

Fig 4. Individuals high in Sexual Excitation (SE) exhibited an improvement in cognitive sexual inhibition after the application of Transcranial Magnetic Stimulation over the inferior frontal gyrus (IFG) in comparison to stimulating the precuneus or during the control condition.

Table 1. Average indices of cognitive and motivational sexual inhibition across the three sessions.

Policy Recommendations: 

  1. As the above results confirm that TMS can be a partial rather than a complete solution, further research is required to investigate the effect over other brain regions to target motivational sexual inhibition. The present protocol can be tested more extensively in clinical samples, as cognitive sexual inhibition has a potential effect over behaviour and refined.
  2. Further research can be undertaken to investigate the effect over other brain regions to target motivational sexual inhibition as the above results confirm that TMS can be a partial rather than a complete solution,.
  3. Overall, there should be investment in research on the biological pathways of sexual offence, as the moral and economical cost of sexual offending is very high. This means exploring further the underlying mechanisms of cognitive failure that is fundamental to design effective treatments for mental and affective impairments. Morally and financially it is highly relevant to invest in research and facilitate the access of innovative treatments to reduce the incidence of sexual offenses in society.

 

  • Fuller A.K. (1989). Child molestation and pedophilia. An overview for the physician. 261,602–6.
  • Young, K. S. (2008). Internet sex addiction: Risk factors, stages of development, and treatment.American Behavioral Scientist, 52(1), 21-37.