Motivation and emotion/Book/2017/Orgasm neurology

Overview
Orgasm is an important aspect of social life, having implications for reproduction, relationships and sexuality (Levin, 2014). While there has been widespread interest in human orgasm in the wider social community, only recently has scientific research begun to explore what occurs in the brain during orgasm. The purpose of this chapter is to answer the question "what happens to the brain during orgasm?". In order to effectively answer this question, research surrounding three main areas will be discussed: brain structures: neurotransmitters, hormones, and non-genital orgasms. By focusing on these three areas, a sufficient understanding of orgasm neurology will be reached.

Questions to be addressed:
 * What is an orgasm?
 * What brain structures are involved?
 * What else occurs in the brain during an orgasm?
 * Are there any gender differences?
 * Can an orgasm occur without genital stimulation?

What is an orgasm?
The word orgasm is derived from the Greek word orgasmos meaning "swollen" or "excited" (Georgiadis, 2011). An orgasm involves physiological, mental and emotional characteristics that are experienced at the peak of sexual excitement through sudden discharge (Georgiadis & Kringelbach, 2012). For males, orgasms result from the stimulation of the penis, while they are the result of clitoris stimulation for females (Georgiadis & Kringelbach, 2012). In both sexes an orgasm includes a loss of control, feelings of release, involuntary muscular contractions, and sharp peaks in cardiovascular arousal (Holstege et al., 2003). Furthermore, an orgasm can be achieved alone through masturbation or with a partner.

{Which of the following does an orgasm not necessarily involve? + Feelings of love. - Involuntary muscular contractions. - Feelings of release. - Loss of control.
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Brain structures


Decades of studies examining the brain and its relationship to the human orgasm have demonstrated there are many brain structures involved in and impacted by an orgasm (Georgiadis, 2011). Importantly, these brain structures are involved in the physical, emotional and mental aspects of orgasm. Interestingly, the brain structures involved in sexual responses, meaning arousal, orgasm and resolution, are similar to those structures involved in other pleasurable activities such as eating (Levin, 2014). This suggests just how important sexual activity, especially orgasm, is.

The prefrontal cortex
The prefrontal cortex (PFC) is an area of the brain located at the front of the frontal lobe and is implicated in an array of functions, including personality development, impulse control, and control and organisation of emotional reactions (Siddiqui, Chatterjee, Kumar, Siddiqui, & Goyal, 2008). Areas of the PFC play an important role leading up to and during orgasm for both men and women (Holstege & Huynh, 2011). Leading up to orgasm, when sexual arousal becomes more intense, activity in the PFC decreases rapidly (Georgiadis et al., 2006). Studies have shown that this deactivation of the PFC continues during orgasm (Georgiadis et al., 2006; Holstege & Huynh, 2011 ).

One of the major areas that demonstrates this deactivation before and during orgasm is the dorsomedial PFC, which is best known for the role it plays in moral reasoning, social judgement and self-awareness (Forbes & Grafman, 2010; Mitchell, Heatherton, & Macrae, 2002). Georgiadis and colleagues (2006) argue these elements are changed dramatically during sexual activity. Due to this, Georgiadis (2011) argues that deactivation of the PFC decreases moral thinking, judgement, and self-awareness, making an individual more relaxed, stress-free and impulsive. Georgiadis (2011) concludes that deactivation of the PFC plays a role in reaching and completing an orgasm.

The orbitofrontal cortex
The orbitofrontal cortex (OFC) is an area found in the PFC and is comprised of several distinct regions, each having their own specific functions (Rolls, 2004). Research suggests the OFC plays a major role during orgasm in both men and women (Georgiadis, Reinders, Paans, Renken, & Kortekaas, 2009). Studies have found that during orgasm the OFC shows significant deactivation in various regions, through a decrease in regional cerebral blood flow (rCBF) (e.g. Georgiadis et al., 2006; Georgiadis et al., 2009).

Georgiadis et al., (2009) argues the most prominent region that reliably shows deactivation is the lateral OFC. Georgiadis et al., (2006) argues the decreased activity in the lateral OFC represents sexual disinhibition and a lack of sexual restraint. This is based on research showing that damage to the OFC results in antisocial, impulsive and disinhibited behaviours, such as sexual disinhibition (Yang, Raine, Lencz, Bihrle, LaCasse & Colletti, 2005). Importantly, this could explain why people describe a loss of conscious control while experiencing an orgasm (Mah & Binik, 2001). However, it’s interesting to note that during genital stimulation without orgasm the lateral OFC shows increased activity (Georgiadis et al., 2006). It is believed this represents high inhibition, as individuals are attempting to control and hold off their orgasms.

A second, less researched region that is deactivated during orgasm is the medial OFC (MOFC) (Georgiadis et al., 2009). The MOFC is thought to be a crucial element of the neural network underlying a person's self-monitoring and self-referential thought (Northoff, Heinzel, Bermpohl, Dobrowolny, Panksepp, 2006). According to Hariri (2000), the deactivation of this network results in a more relaxed state of mind. Therefore the deactivation of the MOFC results in a deactivation of this network, making the orgasm experience a more carefree experience (Georgiadis et al., 2009).

The cerebellum
The cerebellum is located in the hindbrain, one of the lowest brain structures, and plays a key role in motor control, balance and some cognitive functions (Wolf, Rapoport & Schweizer, 2009). Increased activation takes place in the cerebellum during orgasm (Georgiadis et al., 2006). The main area this activation is found is the left deep cerebellar nuclei, extending to the anterior lobe of the cerebellum vermis (Georgiadis et al., 2006). Researchers have suggested two main arguments for why this activation occurs.

The first argument concerns the physical movements made during an orgasm. The cerebellum controls muscle tension, which reach peak levels during orgasm (Komisaruk and Whipple, 2005). Komisaruk and Whipple (2005) argue this suggests the cerebellum plays an important role in the muscular movements that occur during orgasm. Additionally, the anterior lobe of the cerebellum vermis is central for the control of the genitalia and axial muscles found in the pelvic floor (Georgiadis et al., 2006; Georgiadis & Kringelbach, 2012). These two areas are strongly implicated in sexual activity and orgasm (Georgiadis & Kringelbach, 2012). Due to this, researchers argue that the activation found in the cerebellum during orgasm is related to motor control (Georgiadis et al., 2006).

The second argument focuses on the emotional aspects involved in an orgasm. The cerebellum has been shown to be involved in emotional functions (Turner et al., 2007). As a result of this finding, it is believed that the cerebellum is activated due to the emotional responses that occur during an orgasm (Holstege et al., 2003). However, little is known about how and why this occurs or the emotional processes that are actually involved. Due to this, more research needs to be conducted.

The nucleus accumbens


The nucleus accumbens (NAc) is located in an area of the brain called the basal forebrain and its most widely known function is its involvement in the reward circuit of the brain (Dafny & Rosenfeld, 2017). This means that when we do something that is considered rewarding, such as eating food, taking drugs, or having sex, the NAc is activated (Dafny & Rosenfeld, 2017).

Researchers have found the NAc is activated during orgasm for both genders (Georgiadis & Kringelbach, 2012). Bianchi-Demicheli and Ortigue (2007) argues this is due to its involvement in motivation and reward expectation. This expectation results from the "rush" an individual experiences when they orgasm, which motivates wanting to experience one again. This is similar to drug addicts and the high they experience as a result of drug use (Dafny & Rosenfeld, 2017). As a result, Bianchi-Demicheli & Ortigue (2007) suggest that future motivation for orgasm is enforced by each orgasm an individual experiences due to the rewarding experiences.

The periaqueductal gray
The periaqueductal gray (PAG) is the gray matter located in the midbrain, and is involved in a number of neurobiological functions such as pain modulation, anxiety, reproductive behaviour and defensive behaviour (Linnman, Moulton, Barmettle, Becerra, & Borsook, 2012). In a study conducted by Georgiadis et al. (2006) it was found there was stronger activation in the PAG for men compared to women. They argued this could be due to the role the PAG plays in reproductive behaviors specific to males, such as the reproductive purposes of ejaculation. However, there is insufficient research concerning the PAG, the role it plays in orgasm, and gender differences. Due to this, exploring these elements could provide researchers with a better understanding of the differences in male and female orgasm.

Table 1.

Overview of the Brain Structures involved in Orgasms, their Functions, Activation status and Gender differences

Neurotransmitters and hormones
Neurotransmitters (NT) and hormones are both important chemical mechanisms found within the human body. A NT is a chemical messenger that carries and boosts signals between neurons, nerve cells and other cells in the body (Lodish, Berk & Zipursky, 2000). They are constantly working to keep the brain functioning, and manages everything from our heartbeat and breathing to our moods and emotions (Lodish et al., 2000). Hormones are another messenger system, and play a critical role in communication between the body's cells and organs (Neave, 2008). They affect how the body functions, from how the body breaks to down food to growth and sexual development (Neave, 2008).

Dopamine


Dopamine is a neurotransmitter that is believed to be involved in a number of human mechanisms, including reward-motivation behaviour (Levin, 2014). An abundance of evidence points to dopamine as a key neurotransmitter involved in stimulating human orgasm (Kruger, Hartmann & Schedlowski, 2005; Levin, 2014). According to Levin (2014), a simplistic but effective explanation is that dopaminergic transmission is prosexual, meaning it promotes orgasm. Studies have found that leading up to and during orgasm, dopamine levels increase drastically (Levin, 2014). During ejaculation in men, dopamine-synthesising neurons found in the lower brainstem are significantly activated (Holstege et al., 2003). Further studies have found that dopamine neurons in the nucleus accumbens are activated during orgasm in women (Komisaruk et al., 2004). These two activations result in an increase in the release of dopamine neurotransmitters in the brain. Due to this, these findings suggest that the dopaminergic system plays an important role in the male and female orgasm.

Studies looking at the effect of certain drugs have shown that dopamine has an effect on sexual activity and orgasm. A major finding is that dopamine agonists, which are compounds that activate dopamine receptors, have been shown to facilitate human sexual behaviour and orgasm (Kruger et al., 2005). An example of this is the treatment of Parkinson's disease with apomorphine, which is a receptor agonist (Kruger et al., 2005). The use of apomorphine resulted in hypersexuality, which is understood to be extremely frequent or increased libido (Bowers, Van Woert & Davis, 1971). This drug illustrates the role that dopamine plays in orgasm. However, it is important to note that researchers do not yet fully understand the dopamine mechanisms that are involved in sexual behaviour and orgasm (Levin, 2014).

Serotonin
Serotonin is a neurotransmitter that is thought to be involved in feelings of well-being and happiness in humans (Young, 2007). Research indicates that high levels of serotonin can have an inhibitory effect on arousal and orgasm (Georgiadis, 2011; Levin, 2014). This is most common in individuals who take selective serotonin reuptake inhibitors (SSRIs), which block the uptake of serotonin, resulting in increased levels (Levin, 2014). According to Levin (2014), while all phases of sexual arousal can be impaired, the SSRIs most greatly impact on an individual's ability to achieve orgasm. Most research in this area has been focused on male erections and ejaculation, and has found that SSRIs greatly impair their ability to produce an erection and ejaculate (Kruger et al., 2005). Unfortunately, little is known about its impact on women or why SSRIs impair orgasm, meaning more research needs to be conducted.

Oxytocin
Oxytocin (OXT) is a powerful and important hormone involved in the regulation of social interaction and sexual reproduction (Magon & Kalra, 2011). Due to this, it plays a significant role in maternal behaviours such as milk release and infant-mother bonding, empathy, group and partner bonding, and orgasm (Magon & Kalra, 2011).



Research has found that OXT plays a role during orgasm for both men and women (Carmichael et al., 1987; Hurlemann and Scheele, 2016). OXT is believed to play a preparatory role, preparing the penis and vagina for orgasm through muscle contractions and lubrication of the areas (Veening, de Jong, Waldinger, Korte & Olivier, 2015). This conclusion was reached due to the presence of OXT receptors on the male and female genitalia (Gimpl & Fahrenholz, 2001; Veening et al., 2005). Furthermore, studies have found that OXT levels are increased during an orgasm (Carmichael et al., 1987; Hurlemann and Scheele, 2016). Originally, this was thought to be due solely to the muscular movements involved in an orgasm, such as the movements of the pelvic floor for women (Carmichael et al., 1987). While this has not been disproven, more current research has had a greater focus on the emotional aspect of OXT.

The release of OXT has been linked to feelings of well-being, improved social interaction and trust (Churchland & Winkielman, 2012). According to Levin (2014), these changes all take place during an orgasm. Due to this, it has been suggested that the release of OXT during orgasm strengthens the emotional tie between partners (Georgiadis & Kringelbach, 2012; Levin 2014). In addition to this, OXT increases during orgasm have been linked to increases in the intensity of the orgasm (Veening et al., 2005). It is not fully understood why this occurs, but Behnia and colleagues (2014) suggests that it is related to the perception of the relationship for women and physical performance for men.

{Researchers were treating which degenerative disorder when they discovered the effects of dopamine on human orgasm? - Alzheimer's disease. - Huntington's disease. + Parkinson's disease. - Cancer.
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Non-genital orgasm
The brain can work independently of the genitalia to generate an orgasm (Komisaruk & Whipple, 2011). Research has been conducted to determine other ways humans can experience an orgasm without genital stimulation. Here we will be discussing the most common forms of non-genital orgasm but many other forms exist such as imagery, anal stimulation and sleep (Komisaruk & Whipple, 2011).

Breast and nipple


Komisaruk and Whipple (2011) report that women have experienced orgasms through stimulation of the breasts and nipples. The orgasm-inducing effect of breast or nipple stimulation is believed to be due to the sensory activity from these areas projecting the same neurons that receive sensory information from the genitals. These neurons produce oxytocin into the brain, bloodstream and spinal cord in response to the stimulation, which seems to play a role in pleasurable experiences involved in an orgasm.

Spinal injury
Women who have complete spinal cord injury above T10 (i.e., above the level of entry to the spinal cord of specific sensory nerves) can still experience orgasm (Komisaruk et al., 2004). Studies have shown that women who are vaginally stimulated even though they have no bodily feeling are still able to experience orgasms, and researchers have called these non-genitalia orgasms (Komisaruk & Whipple, 2011). The main theory for why this occurs concerns the Vagus nerve, which is the longest nerve in the autonomic nervous system and connects areas such as the genitals, anus and pelvic floor to the brain (Komisaruk & Whipple, 2011). Due to this, it is believed that the Vagus nerves provide a spinal cord bypass for vaginal awareness in women who have complete spinal cord injury, stimulating brain areas which enable women to still experience orgasm (Komisaruk et al., 2004).

Epileptic seizures
Both men and women have reported orgasmic feelings just before the onset of an epileptic seizure, referred to as an "orgasmic aura" (Georgiadis, 2011)). Genital stimulation does not have to occur for orgasmic aura to occur, instead they are either spontaneous or may be triggered by some specific stimulus (Komisaruk & Whipple, 2011). For example, one woman experienced orgasmic aura whenever she brushed her teeth (Chuang, Lin, Lui, Chen, & Chang, 2004). Evidence suggests the most common brain region these orgasmic auras originate from is the right temporal lobe (Komisaruk & Whipple, 2011). However, it is still unknown why orgasmic auras actually occur, but Georgiadis (2011) suggests it could illustrate the importance of the temporal lobe in orgasm experiences.

Conclusion
This chapter shows the importance of the brain in the orgasmic experience. The involvement of numerous brain structures, neurotransmitters and hormones in human orgasm is important. It demonstrates that an orgasm results from widespread of neural deactivation and activation, as well as the increase in neurotransmitters and hormones. Furthermore, it demonstrates that our understanding of human orgasms helps us to understand relationships and bonding, emotions, and reward processing.

However, the majority of research exploring orgasm neurology took place in the 1970s and 1980s, with newer research only confirming or reiterating past findings. While this helps to strengthen our findings and what we know about orgasms, it does mean that there is not a lot of new and exciting research taking place. For example, it would be beneficial to our understanding about human relationships to further explore the role of the cerebellum in emotional processing during orgasm. Due to this, more research should be conducted into orgasm neurology in order to better understand the mechanisms of the brain and the role they play in human orgasms.