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ОглавлениеBiological Drive Profile (BDP) Factors
Many biochemical processes are involved in human sexual behaviour: some activating the sexual response; others inhibiting it. Some of these processes are similar in both male and female; others are different. Genetic and developmental factors play a role, not least in the regulatory functions of the brain and hormonal system. These biological processes are also found in nonhuman mammalian species, so that generalisations from animal research have some justification, although non-human species are unaffected by the overlay of political, sociocultural, moral, and gender issues.68 The combined activity of the biochemical processes activating and inhibiting sexual motivation at any particular time forms the basis of the prevailing BDP, and this I now outline.
A study of brain regions associated with sexual desire and arousal or inhibition gives insights into the biology of the sexual response. However, it is difficult to separate the brain’s activity as a biological source motivating sexual behaviour, from its role as a processing mediator creating a physiological response to the ideas and perceptions generated by the subjective self. The neuroendocrine system is a key player in sexual motivation and sexual behaviour (and in reward systems more generally), producing various neurochemicals including hormones, peptides and neurotransmitters.69 We find that although neuro-biological systems are involved in both priming sexual interest and in the expression of sexual behaviour, it plays a lesser role in the reason, focus and object of this interest and behaviour (why and with whom I might want to have sex), the latter being mediated by subjective attributions relating to the sexual object. This drive source is also independent of the perceived meanings of behaviour: at this level, it is the sensory experiences that become the stimulus for sexual interest or arousal.
Genetics and sexual predispositions
Biological systems find their origin in genetics. However, the interplay of environment and physiological development can make it difficult to disentangle those aspects of our biological makeup that are fully determined by genetics, and those which are only partially so determined. It is now recognised that many characteristics with a genetic base nevertheless require environmental events to activate their expression. Wieten (2001) observes: ‘the impact of genetic makeup depends on the environment, and the impact of the environment depends on genetic makeup’ (p. 86). While there is no doubt some genetic contribution to a person’s hormonal profile,70 what we do know is that the environmental contribution to that profile is significant. Twin studies are routinely used on the basis that identical twins share identical genetics, while non-identical twins share the same uterine and family environment, but not identical genetics. Strictly speaking, if something is governed by genetics alone, we would expect a 100% correspondence for identical twins, and some smaller percentage for non-identical twins. Typically, when a less than 100% correspondence is found, we talk of genetic predisposition. But this leaves open the question of the nature and extent of such genetic contribution.
When it comes to sexual behaviour, twin research has largely centred on the question of sexual orientation. Questions relating to interpersonal variation in hormonal profiles and temperament and personality factors in sexual attraction and desire have received little attention. Although the nature/nurture debate has long featured in personality research, the extent of the role of genetics in these individual differences remains unclear. Nevertheless, whatever the extent of genetic involvement, research has linked certain personality and temperament characteristics to certain sexual behaviours. For example, extraversion has been linked to having more sexual partners71 and to sexual risk-taking,72 while interpersonal assertiveness and dominance have also been linked to having more sexual partners.73 Also people who are sensation-seeking, that is, who tend to pursue thrilling and risky activities (perhaps to compensate for lower levels of dopamine74) are more likely to be unfaithful75 and to engage in risky sexual behaviours with larger numbers of sexual partners.76
Returning to the question of the genetic contribution to sexual orientation, we find relatively low percentages of such contribution have been found in twin studies. Rosario and Schrimshaw suggest that there is a lack of significant findings in more representative samples of the population when it comes to large familial (sibling versus identical versus non-identical twin) studies. They conclude that up to 50% of homosexual orientation may be attributed to genetic factors ‘of some kind’.77 In fact, feminine behaviour in boys, which the intra-uterine hormonal environment contributes to, appears to be a much stronger predictor of male homosexuality.78 Either way, there remains a significant proportion of men experiencing same-sex attraction for reasons other than genetic predisposition and feminine inclinations. This is certainly also true of women, where a greater incidence of sexual fluidity is reported. 79
Neurochemicals and the sexual response
The biological mechanisms underlying sexual desire, arousal, and expression involve many different elements. Not least of these is the timely release of various neurochemicals, some of which activate sexual priming and some of which inhibit it. The continually changing composition of these neurochemicals forms an important component of the BDP.
Let us first consider the neurochemicals associated with sexual arousal. Dopamine and melanocortins are released in the hypothalamus and limbic regions when a person is exposed to various sexual cues, heightening attention and desire: these associate with generating sexual interest. Dopamine is typically associated with expectation of reward, and in its link to encoding expectation of reward, it plays a role in the conditioning process — but also in addiction. This alerts us to the addictive potential of sexual behaviour.80 Dopamine release has a role in ‘sexual wanting’. It links with anticipation, excitement, desire, concentration, memory, and learning, as well as enhancing the feeling of meaningfulness in things. It has been linked with sociability, but also to social anxiety.81 It is not surprising then, that those with a predisposition to high levels of dopamine are more likely to be involved in sexual activity early, and to have many sexual partners.82 Dopamine interacts with the hormonal profile. Oestradiol and testosterone can facilitate dopamine activation,83 while dopamine can also stimulate hormone release mediating the body’s fight-and-flight response — which may not be so good for the relationship itself. Critical as dopamine activation is to the sexual reward system, it needs to act in concert with other neurochemical and subjective factors to find expression in any particular sexual impulse.
The neurochemicals noradrenaline, oxytocin and vasopressin are also associated with sexual arousal. Noradrenaline (or epinephrine) helps regulate sexual arousal and motivation.84 Meanwhile, oxytocin and vasopressin are released just before orgasm in both men and women, playing a role in pleasure (motivating future sexual activity), but also in emotional attachment to the person with whom the orgasm is experienced.85 This mechanism (along with the role of dopamine) can be understood within the classical conditioning paradigm. Lehmiller (2014) notes that the release of oxytocin plays ‘a vital role in developing bonds between romantic and sexual partners because it is released during physical intimacy’ (p. 99),86 while Toates (2014) suggests that the raised oxytocin levels in women following orgasm could ‘consolidate the incentive value of the partner and sense of belonging with this person’ (p. 108). We see here that belonging is not only created by the sense of shared personal space and experience, but is also supported by a biological link between the sexual event and bonding.
Of course, oxytocin is not only featured in the sexual encounter. It is also released in parent-child bonding which should be anything but sexual. But there is other hormone activity present in the adult sexual profile to distinguish these events — the release of vasopressin and testosterone, for example.87 We see here the finely tuned balance of a neuroendocrine system that lays the biological basis for relational experiences; but also the interplay between the bonding qualities of oxytocin and vasopressin, and the territorial and protective aggressiveness with which testosterone release might be associated. Here the source of the bonding experience which associates with belonging is a chemical one. It is easy to see the potential for confusion in regard to the interpretation of one’s experiences of intimacy and belonging; that is, to sexualise a nurturing event, or to feel connected in a sexual event where there is otherwise little emotional connection.
With regard to the activation of various brain regions, the orbitofrontal cortex, the prefrontal cortex and the anterior cingulate cortex may be involved in the evaluation of sexual attractiveness. Other regions of the prefrontal cortex and the anterior cingulate cortex may play a role in sexual desire through the evaluation of the reward value of external reward stimuli.88 Diamond & Dickenson (2012) report that activation of the caudate, insula and putamen brain regions appear to relate both to the experience of sexual desire and romantic love. Pfaus, et al. (2014) note that because of the extensive anatomical and functional connections these neural areas have with many other parts of the brain, ready access is allowed to contextual information to inform both the judgement of sexual attraction and the stimulation of sexual desire. This represents the neural parallel of the many associations made at a subjective and meaning level, and underscores the complexity of the sexual experience.
However, as the arousal level associated with sexual pleasure is prolonged, neural changes occur in regions of the amygdala and the frontal and prefrontal cortex. This adversely affects capacity for moral affiliations, self-other relations, self-awareness, and interpersonal judgements.89 (Perhaps the reverse is also true: that is, that a strong focus on moral affiliations, self-other relations, self-awareness, and interpersonal judgements act to inhibit sexual arousal and sexual pleasure by way of increased activity in these same regions.) Pfaus, et al. (2014) suggest that the function of such neural changes is to help ‘dissolve normal body boundaries, thereby facilitating sexual interactions, which in turn might contribute significantly to the experience of sexual arousal’ (p. 174). We observe here a neural equivalent to the notion of shared subjective space in the experience of sexual activity. During orgasm, reward-related regions of the limbic system and the cerebellum are activated, while the regions associated with vigilance are inhibited.90 Simply put, prolonged sexual arousal negatively affects a person’s capacity for objective judgement.
When it comes to sexual inhibition, other neurochemicals are involved. Some prevent a sexual event occurring in the first place; others bring a sexual event to an end. Opiods, for example, are released in the cortex, limbic system, hypothalamus, and midbrain during orgasm, and mediate sexual reward. In providing the experiential reward found in sexual pleasure and thus serving to sate the drive, its release quickly reduces sexual desire and arousal.91 Both serotonin (which counters the effect of dopamine) and endogenous cannabinoids are released immediately after a sexual event, shutting down sexual arousal, with serotonin creating a sense of peace and sexual satiety, and endogenous cannabinoids mediating sedation.92
Not only does sexual inhibition immediately follow orgasm, it can also result from stress or threat.93 However, the latter is subject to individual differences in perception of the degree of threat: a limited amount of stress or threat can have the reverse effect, stimulating arousal for some (especially in those with a high threshold for the capacity to be aroused) but creating inhibition in others. Generally, stress is associated with negative emotions: of guilt, fear, anger, grief, and shame. These emotions result in cortisol release, contributing to inhibition of sexual arousal. In conditions of sexual inhibition, those areas in the forebrain relating to good judgement, alertness, and saliency detection are activated, preventing focus on sexual desire and arousal.94 Dual-control theories of sexual arousal such as Perelman’s sexual tipping point dual control model95 have been structured around the competing neurochemical activities that determine whether sexual excitation or inhibition ultimately occurs.
The hormonal profile: Priming for sexual desire
We now look at the changing hormonal profile which plays a role both in the priming of sexual interest and in the activation of sexual arousal. Determining the hormonal contribution during various periods of development and determining the effect of various contexts on the hormonal profile is difficult, both in the measurement of hormonal fluctuation and in the isolation of variables — not only in relation to what might result from hormonal change, but also in relation to what might contribute to it. Nevertheless, it is clear that hormones influence sexual desire in the most general sense, and that various neurochemicals are activated both in the process of sexual arousal and in the subsequent sexual encounter. In a woman, for example, the rhythm of sexual desire is intimately connected with the biology of her reproductive systems as expressed in her hormonal profile, both in her monthly cycles, and in the seasons of her lifetime.
As is true of other aspects of the mind-body relationship, biochemical and psychological processes interact. And so, for example, subjective mood states can affect the hormonal profile affecting sexual desire, while subjective experiences (for example, sexual thoughts or fantasies) can translate into neuro-chemical activation that creates subsequent conditioned arousal responses to those particular thoughts and fantasies. Furthermore, a person’s hormonal profile is in a constant state of flux,96 responding to physiological events (the internal biological context, such as the menstrual cycle and pregnancy in women97), to external circumstances (the prevailing environmental context, such as relationship circumstances), and to developmental and life-cycle changes. The prevailing hormonal profile at critical developmental periods can also have enduring effects, especially when it contributes to subjective associations and conditioning processes. That is, hormones can activate or inhibit certain sexual behaviours at one time, which creates implicit memories affecting later sexual behaviour.
On the basis of such research as has been done in this area, we have glimpses into the complexities of the interaction of the hormonal profile and these various factors. But we begin with the reminder that although both men and women carry the hormones testosterone and oestrogen, their profiles are different. Testosterone, a hormone of the androgen group, has been associated not only with the development of male physical sexual characteristics, but also with the regulation of cognitive and physical energy. Testosterone associates with sexual motivation in men, although it does not affect the ability to engage in sexual activity.98 In women, the release of oestrogen relates to sexual motivation, while release of progesterone has the reverse relationship.99
But the effect of the hormonal profile on sexual behaviour begins long before men and women develop sexual interest. It begins before birth, as a mother’s hormonal activity affects the baby within her. The sperm fertilising the egg determines whether the baby will be male or female. However, the baby’s physical masculine or feminine characteristics is shaped by the mother’s prevailing hormonal profile during the first trimester of her pregnancy. The correct concentration of testosterone at the right time is prerequisite to the physical development of male features; otherwise, female features develop. This in turn sets the biological framework for later patterns of sexual attraction and desire as the baby grows and eventually enters adulthood.
During the second trimester, evidence suggests that the mother’s androgen levels shape aspects of the baby’s brain, influencing gender formation. Testosterone (converted to oestradiol) contributes to masculinisation in interest and behaviour. Too much testosterone can have a masculinising effect on a developing girl, so that she later comes to prefer ‘male’ toys, activities, and playmates, has decreased interest in feminine behaviours such as playing with dolls, is more socially detached, engages in less verbal aggression (but more physical aggression) and is later less likely to have exclusively heterosexual orientation.100 In corresponding manner, a deficit of androgen hormones prenatally may lead to a ‘predominantly female differentiated brain’ which in a boy has been associated with later homosexual tendencies.101
The idea that sexual orientation may be influenced by brain development under the influence of hormonal secretions during critical periods of prenatal development has also found other support.102 For example, a higher incidence of lesbian orientation has been found among women exposed prenatally to a synthetic hormone used to reduce miscarriage (in their mothers) as well as among women with an adrenal disorder resulting in abnormally high androgen levels during prenatal development.103 However, while there is evidence that sexual orientation is affected by prenatal masculinisation or feminisation processes, there is no evidence of the biological inevitability of sexual object choice.104 Moreover, the subsequent prevailing hormonal profile in an adult does not appear to determine the choice of erotic desire: when the hormone levels of homosexuals and heterosexuals were compared, no consistent links with sexual orientation were found.105
The hormonal profile changes over the life cycle, and does so differently for men than for women. Sexual interest, desire, and arousal often begin before puberty, around age ten, for both boys and girls with the maturation of adrenal glands (adrenarche).106 Hormone levels begin to change (with sexual interest and hormonal changes influencing each other), the subsequent onset of puberty being managed by hypothalamic sexual control centres.107 Testosterone levels surge for pubescent boys while pubescent girls experience increasing levels in both testosterone and oestrogen.108 This results in maturation in primary and secondary sexual characteristics, in increased risk-taking and increased sexual interest and activity in boys, and in depression and identity concerns in girls. Unlike its associations with sexual ideation and motivation in boys, testosterone elevation does not relate strongly to sexual activity in girls.109 Generally, as testosterone levels begin their steep incline, any potential issues with sexual identity or orientation emerge.110 Nevertheless, the object of sexual interest appears fluid, especially to begin with. It is not defined by the prevailing hormonal profile: for some boys and for reasons other than hormonal activity, the object of their emerging sexual interest may be other males. These hormonal changes also coincide with changes in relationships with parents, preparing the way for a new attachment with a lover. Perhaps testosterone increase plays a role in motivating the leaving one for the other, along with the establishment of new interpersonal territory. Testosterone levels peak during the 20s, followed by a gradual decline.
Although hormonal levels begin their gradual decline in the 20s, fluctuations continue to occur, affected by both physiological and environmental factors. Testosterone and oestrogen levels fluctuate daily, peaking early in the morning before waking; while seasonal variations also occur, with testosterone levels increasing in autumn in both men and women. Another source of fluctuation is the menstrual cycle in women. Sexual motivation varies systematically during this time. During the peri-ovulatory period of the menstrual cycle, the hormonal profile is characterised by high oestrogen levels and low progesterone levels, with accompanying increase in sexual motivation and likelihood of sexual fantasies,111 and in greater sexual interest in men — including men other than their current partner.112 Lesbian women (and to a lesser extent, bisexual women) report a similar increase in sexual interest (in women) during the oestrogen peak of their cycle, although interest in the opposite sex reportedly decreases.113 The perinatal period in a woman sees dramatic changes in her hormonal profile, lowering sexual interest and enjoyment. With advancing age, testosterone levels continue to drop in men while oestrogen and androgen drops during menopause in women. These changes see a decline in sexual desire and motivation.114
Relationship circumstances also affect hormonal profiles, although results vary. Again, testosterone has received most research attention. It seems testosterone levels are higher in more sexually active men,115 for single men with past relationship experience,116 and in men who have sex with more than one person or with an unfamiliar person.117 Continued high testosterone levels seem to associate with instability in a sexual relationship: there is an association between men with high testosterone levels and the likelihood of extramarital sex, or divorce.118 Some research shows that falling in love decreases men’s testosterone levels (simultaneously increasing cortisol, suggesting that falling in love is a stressful event; but the lower testosterone level also suggests that sexual desire may not be the primary drive in the ‘falling in love’ event) but then, as the relationship becomes more certain, testosterone levels are gradually restored.119 Other research suggests testosterone levels are again reduced once a man settles into a long-term relationship,120 or his focus shifts from sexual matters to his children.121 Parenthood has been linked with lowered testosterone in both men and women. It may be that the need for sexual priming is reduced, and biological processes are responsive to this. But another interpretation may be that testosterone levels in males drop once the business of establishing territory and belonging is completed.
Context also affects the hormonal profile. Various studies give insights in how the hormonal profile might react to perceptions and external events: again, these studies generally measure testosterone levels. For example, it seems testosterone is released (along with accompanying optimism and energy levels) as a man watches a sexually explicit movie, peaking some sixty to ninety minutes after the movie has been seen, whereas such a release does not occur when a sexually neutral movie is watched.122 No doubt similar testosterone release occurs in relation to viewing pornographic material and whilst engaging in sexual fantasy. Testosterone levels can increase as a man has a brief conversation with a woman, perhaps with the intent to impress her,123 and more generally (depending on initial level of arousal), when a male relates to a novel female.124 These findings have implications for the possible effect of exposure to sexual situations (including sexual abuse, sexualisation of relationships, sexualisation in the media, and pornography) on the prevailing testosterone levels in males.
Sexual conditioning: The impulse that repeats the past
While hormones play a role in priming and energising sexual behaviour, other neural systems also contribute to shaping sexual behaviour through behavioural conditioning. Classical (or Pavlovian) conditioning has to do with pairing a neutral stimulus with another stimulus that evokes an automatic response. In this context, a pairing might occur of sexual arousal with a particular image or object. Operant (or instrumental) conditioning has to do with what sexual behaviours are reinforced or punished: this determines whether such behaviours are likely to occur again. Our interest is especially in classical conditioning, which involves automatic physiological responses governed by implicit memories. Being an automatic function of the brain rather than being governed by personal choice, it finds its place as part of the BDP, rather than the SDP. Such conditioned pairing of object or context with a sexual response may be advantageous; but it may also result in a contamination of association, where neural networks make unwanted connections between various stimuli, including ideas and experiences. In the realm of sexual behaviour, this generally means unwanted sexual arousal triggered by various objects, thoughts or contexts; or alternatively, unwanted sexual inhibition triggered by certain thoughts or contexts.
In their research with animals, Pfaus, et al. (2014) found that neutral cues were easily conditioned to sexual desire, arousal, and copulatory behaviour. They explain ‘although sexual behaviour is controlled by hormonal and neurochemical actions in the brain, sexual experience induces a degree of plasticity that allows animals to form instrumental and Pavlovian associations that predict sexual outcomes, thereby directing the strength of sexual responding’ (p. 147). They further propose that ‘endogenous opioid activation forms the basis of sexual reward, which also sensitises hypothalamic and mesolimbic dopamine systems in the presence of cues that predict sexual reward. Those systems act to focus attention on, and activate goal-directed behaviour toward, reward-related stimuli’ (p. 147). That is, even though hormonal processes might activate the animal’s ‘sex drive’, learning processes, mediated by dopamine release, were then involved in creating associations with the object or focus of sexual interest, thus affecting later behaviour. The conditioning process stimulated pair-bonding so that an animal would seek out a sexual partner bearing the cue to which it had been conditioned — yet another mechanism connecting sexual activity with the sense of belonging.
Animal studies also show that the environmental cues that come to be associated with opioid release occurring during sexual climax can activate hormonal activity, priming both males and females for sexual activity.125 The hormones priming for sexual activity can in turn be stimulated by environmental factors previously associated with sexual activity. Pfaus, et al. (2014) observe that ‘sexual behaviour epitomises the whole-body relationship between autonomic activation and central nervous function. Yet part of that biological substrate is an enormous adaptive flexibility in the brain that allows individual and idiosyncratic Pavlovian and operant associations to be made between external stimuli, behavioural responses, and sexual reward’ (p. 184). In other words, an animal learns to be sexually aroused by things that happen to be associated with sexual arousal in the past.
This conditioning principle predicts that the cues associated with sexual arousal in the past can later contribute to the stimulation of sexual desire. That is, a history of sexual arousal in a certain context can create sexual desire in relation to that context. Sexual arousal can lead to sexual desire, just as sexual desire can lead to sexual arousal. This principle can play a critical role in the development of various sexual fetishes, but also in the longer-term effects of certain fantasies and exposure to various erotic stimuli. And so, for example, because difference is an important arousal factor, an adolescent may access increasingly risqué pornographic images (involving, for example, same-sex situations, multiple sexual partners, sexual violence, children, etc.), and sexual arousal responses then become conditioned to those stimuli. A person learns to sexually desire those things that sexually aroused him in the past.
The principles of conditioning theory have also underpinned various therapeutic interventions in sexual behaviour (particularly in the 1960s and 1970s, when a different political climate prevailed regarding acceptable targets for sexual behavioural change). These interventions included ‘orgasmic reconditioning’,126 aversive control procedures, and desensitisation (habituation) procedures,127 practiced especially in relation to homosexual behaviours. That is, therapy was based on the idea that changes in sexual behaviour and orientation could be learned because of the inherent ability of the brain to adapt to experience. Not surprisingly, such therapy had mixed results given the overall complexity of the sexual response. Success was much more likely when therapeutic goals were aligned with personal desire for change, based on other subjective drive factors.
All this means that the early circumstances of a person’s sexual experiences may be significant from a conditioning perspective. Animal research suggests that initial sexual experiences play a critical role in shaping sexual responses to particular stimuli. Pfaus, et al. (2014) explain: ‘a critical period exists during an individual’s early sexual experience that creates a “love map” or Gestalt of features, movements, feelings, and interpersonal interactions associated with sexual reward’ (p.147). They argue that there are critical periods in the development of sexual profiles: ‘certain critical ages and during certain critical events (i.e., first experiences of sexual desire, masturbation, sexual release, first partnered activity), the sensory, cognitive, affective, and motoric aspects of sexuality become fundamentally integrated, organised by direct experience of reward and pleasure… these integrated experiences crystallise into stable preferences for certain sexual acts and certain partner characteristics.’128
Consistent with the principles of classical learning theory, the circumstances and cues that relate to early sexual experiences lay a foundation for subsequent patterns of sexual arousal and sexual desire. This means, for example, that the ‘experimental’ sexual experiences of adolescence can play a significant role in shaping later sexual expectations and orientation. In this regard, Bem wrote: ‘I am willing to entertain the possibility that a process akin to imprinting may also contribute to the eroticization of arousal and the temporal stability of sexual orientation across the life course, again with particular force for the gender-nonconforming child who is taunted by same-sex peers.’129 Initial learning in sexual experience and behaviour creates neural imprints that play a critical role in later sexual behaviour.
And so we see that the reward systems in sexual attraction are complex. While sexual desire is largely anticipatory in nature, the pleasure anticipated in genital stimulation and orgasm constitute a powerful but small part of the possible reward structure a relationship might provide. Indeed, by its very nature, the arousal linked to genital stimulation and the pleasure related to orgasm are brief events that are quickly sated, compared to other aspects of the reward structure. It is this former aspect of sexual reward that lends itself to classical and operant conditioning principles, while other principles are relevant to the other aspects of reward. In other words, the rewards in sexual behaviour are layered, with physical pleasure and release (with the neural system as source) being immediate but short-lived, while the relational rewards (with the subjective self as source) being more subtle and longer-lasting. We now turn to the subjective drive themes.
