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Human Sexual Behaviour in the Brain
Baird AD, Wilson SJ, Bladin PF, Saling MM, Reutens DC. Neurological control of human sexual behaviour: insights from lesion studies. J Neurol Neurosurg Psychiatry. 2007 Oct;78(10):1042-9. doi: 10.1136/jnnp.2006.107193. Epub 2006 Dec 22. PMID: 17189299; PMCID: PMC2117556.
Introduction
The relationship between the human brain and sexual behaviour is intricate. Despite the undeniable importance of this topic, it has historically received limited attention in medical practice and scientific research due to the challenges of quantifying and objectively measuring the deeply personal topic that is human sexuality. Focusing solely on human studies, we examine the use of advanced neuroimaging techniques to uncover the neural processes associated with romantic and sexual responses. However, while these studies identify the brain regions activated during such experiences, they do not definitively pinpoint which areas are essential for specific aspects of human sexual behaviour. To provide a more precise understanding of these connections, we turn to individuals who have suffered neurological injuries, which allows us to investigate the distinct brain regions and sexual behaviours.
The core aim of this review is to compile the existing body of human research in this field, ultimately revealing the critical role of the brain regions “mesial temporal lobes” and “amygdalae” in regulating human sexual desire, thus enhancing our comprehension of the complex orchestration of human romantic and sexual experiences.
To understand how the brain influences human sexual behaviour, it's important to distinguish between two main aspects: disinhibited sexual behaviour, which is when sexual behaviour is part of a broader lack of control, and hypersexuality, which is an intense increase in sexual drive and activity on its own. These two aspects are separated based on where they occur in the brain and how they can be treated. Disinhibited sexual behaviour is linked to injuries in certain brain areas that control self-control, while "true hypersexuality" is more often connected to injuries in different brain areas responsible for emotions and memory. Similarly, a decreased interest in sex, called hyposexuality, can happen either as a result of injuries to a part of the brain responsible for motivation or as an isolated effect in conditions like temporal lobe epilepsy. We focus on understanding hypersexuality and hyposexuality in the context of brain-behaviour relationships.
Brain Regions
The Septal Region
The septal region, a part of the brain's emotional centre, seems crucial in influencing sexual behaviour. Researchers found that stimulating or damaging this area resulted in consistent feelings of pleasure and varying levels of sexual arousal in patients. Electrical or chemical stimulation triggered pleasurable responses. Evidence supporting this link comes from incidents where patients showed heightened sexual interest after surgery, with CT scans revealing that the surgical devices were lodged in the septum. This suggests that the septal region plays a role in pleasure, and possibly regulates sexual behaviour through connections with other brain areas.
The Hypothalamus
Damage to specific areas within the brain, particularly the hypothalamus, has been linked to significant changes in sexual behaviour. For instance, when the hypothalamus is affected by injury or lesions, it can lead to a decrease or even loss of sexual desire and function. Conversely, certain brain injuries or lesions involving broader brain regions, including the hypothalamus, can sometimes result in increased or abnormal sexual impulses. Studies have shown that the hypothalamus plays a crucial role in regulating sexual impulses and is involved in both the physical and emotional aspects of sexual arousal. For instance, experiments on animals and observations from patients with brain injuries have highlighted the hypothalamus' role in controlling sexual behaviour. This brain region seems to initiate and regulate sexual responses, as indicated by its activation during sexual arousal as observed in brain imaging studies.
The Frontal Lobes
The frontal lobes, a part of the brain, play a significant role in regulating sexual behaviour. Damage to these lobes, particularly the orbitofrontal region, can lead to uninhibited sexual actions. Studies show that some people might exhibit increased sexual desire after certain brain surgeries, while others might not experience any changes. Seizures originating in the frontal lobes can cause uncontrollable sexual movements, often misunderstood historically as non-epileptic or hysterical behaviour. Researchers have observed that different parts of the frontal lobes get activated during sexual arousal, indicating their involvement in experiencing pleasure, controlling body movements during arousal, and managing the emotional aspects of sexual response.
The Temporal Lobes
The part of the brain responsible for human sexual behaviour is often linked to an area called the temporal lobes. When these areas are damaged or removed, it can cause a syndrome known as Klüver-Bucy syndrome (KBS). This syndrome includes symptoms like an inability to recognize objects visually, intense reactions to visual stimuli, emotional changes like reduced fear and anger, changes in eating habits, and increased sexual desire. There have been cases where people with KBS displayed hypersexuality, exhibiting frequent and inappropriate sexual behaviour. However, not everyone with temporal lobe damage develops KBS, and while there's a suspected link between this syndrome and damage to structures like the amygdala within the temporal lobes, it's not fully understood. Additionally, studies suggest that early damage to the temporal lobes might be associated with certain sexual deviations.
The Amygdalae
Studies in animals have shown that the amygdala, a part of the brain's temporal lobe, plays a crucial role in controlling sexual behaviour. Recent research explored this in humans who underwent surgery for epilepsy. Patients with increased post-surgery sexual activity had a larger amygdala on the opposite side of the brain from where the surgery occurred, compared to those with decreased activity or no change. This suggests a link between a bigger opposite-side amygdala and enhanced sexuality after surgery, possibly due to its role in processing emotional cues related to sex. Additional evidence comes from instances where stimulating the amygdala caused sexual sensations. Surgical procedures aiming to control severe behaviours have involved damaging parts of the amygdala. Human studies after such surgeries suggest that major changes in sexual behaviour, while possible, are rare and less obvious than in animals, likely due to the complexity of human sexuality.
Conclusion
We've conducted the first comprehensive review of studies exploring how brain injuries affect human sexual behaviour, using findings from functional brain imaging. Our current knowledge is limited and relies heavily on small studies and individual cases. However, there's consistent evidence pinpointing six specific brain areas that influence different aspects of sexual behaviour. Research suggests that the temporal lobes are crucial for sexual behaviour, and the amygdala plays a significant role in controlling sexual desire. This review emphasizes the need for more investigation into how the brain influences our sexual behaviour, aiming to encourage further research, especially into the identified key brain regions.
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