Evolution, mating and bonding

Intimate relationships are far more fragile than most of us realize.

Orgasm

Men versus women on sexual brain function- Prominent differences during tactile genital stimulation but not during orgasm (during the sexual act, differential brain responses across genders are principally related to the stimulatory (plateau) phase and not to the orgasmic phase)

Studying couple harmony/disharmony

• Sexual Satisfaction and Relationship Happiness in Midlife and Older Couples in Five Countries (Men in long-term relationships highly value affectionate touch and sexual caress. More than sex.)
• The components of optimal sexuality: a portrait of "great sex" (Orgasm not vital to great sex - Canadian study)
• Does a Long-Term Relationship Kill Romantic Love? (87% of couples "not romantically in love" long-term)
• Reward, Addiction and Emotion Regulation Systems Associated with Rejection in Love (MRIs of "rejected" partners, showing areas of brain activation)
• Marital behavior oxytocin vasopressin and wound healing (Blister tests - implicating oxytocin and vasopressin in couples' positive and negative communication behaviors, and further evidence of their role in an important health outcome, wound healing)
• Marital Stress: Immunologic, Neuroendocrine, and Automnomic Correlates (even the marriages of happy, well suited, healthy newlyweds in love show signs of radical deterioration by second year of marriage)
• Sexual Motivation and the Duration of Partnership ((1)sexual activity and sexual satisfaction decline in women and men as the duration of partnership increases; (2) sexual desire only declines in women; (3) desire for tenderness declines in men and rises in women)
• Wired for Love: Studying Physiological Reactivity in Married Couples (overview of why we should study couple conflict)
• Marital Happiness, Marital Duration, and the U-Shaped Curve: Evidence from a Five-Wave Panel Study (17-year study showing decline in marital satisfaction)
• Keeping Love Alive (MRIs of two women in love after ten years)
• Effect of Marital Conflict on Healing (account of experiment showing that conflict in marriage slows healing)

Oxytocin

• Oxytocin and male sexual function OT also mediates ejaculation, post-ejaculatory detumescence and the post-orgasm refractory period. OT and OT-receptor in the central nerve system will be a new target in the drug development for the treatment of erectile dysfunction, while OT intracavernous injection promises to be an effective therapy for priapism.
• Dopamine oxytocin interactions in penile erection (1) SHOWS THAT OXYTOCIN PRODUCING CELLS CONTAIN DOPAMINE RECEPTORS. SO DOPAMINE CAUSES INCREASE IN OXYTOCIN.
  2) FOR ERECTIONS, DIFFERENT DOPAMINE RECEPTORS ARE ACTIVATED (WITH DIFFERENT OXYTOCIN PRODUCING REGIONS) DEPENDING ON WHETHER A RECEPTIVE FEMALE IS PRESENT OR NOT. COULD MEAN THAT SELF STIMULATION DIFFERS FROM PARTNER STIMULATION – IN WHAT OXYTOCIN REGIONS ARE ACTIVATED.)
• Oxytocin mediates the antidepressant effects of mating behavior in male mice (OT may mediate the antidepressant effects of mating behavior.)
• Oxytocin mediates the antidepressant effects of mating behavior in male mice (Oxytocin released during mating had antidepressant effect on males.)
• The influence of depressive symptomatology and perceived stress on plasma and salivary oxytocin before, during and after a support enhancement intervention (Four weeks of “warm touch” normalized depressive symptoms.)
• Centrally released oxytocin mediates mating-induced anxiolysis in male rats (Oxytocin critical to change of behavior male rats for several hours after coitus. They take more risks and seem less fearful.) Complete study
• Attenuation of the neuronal stress responsiveness and corticotrophin releasing hormone synthesis after sexual activity in male rats. (After coitus with receptive female rat there is a change in oxytocin neurons and reduced stress response, but oxytocin itself doesn't account for the changes, which still occurred even when oxytocin receptors were blocked.)
• Prolactin secretory rhythm of mated rats induced by a single injection of oxytocin (Oxytocin surge at orgasm may cause post-orgasmic prolactin.) Complete study
• Menstrual cycle-related changes in plasma oxytocin are relevant to normal sexual function in healthy women (plasma OT levels significantly relates to the genital lubrication in both women taking and not taking oral contraceptive pill, apparently confirming its role in peripheral activation of sexual function)
• Social stimuli cause changes of plasma oxytocin and behavior in guinea pigs (oxytocin increases during companionship after mating)
• Blockade of Phosphodiesterase Type 5 Enhances Rat Neurohypophysial Excitability and Electrically-Evoked Oxytocin Release (Viagra plus electrical stimulation in the brain releases oxytocin - but may have little to do with emotional bonding. Also see related article.)
• Oxytocin Improves "Mind-Reading" in Humans (intranasal administration of 24 IU oxytocin improved reading of social cues)
• Prior exposure To oxytocin mimics the effects of social contact and facilitates sexual behaviour in females. (oxytocin increases sexual receptivity)
• Oxytocin maintains as well as initiates female sexual behavior: effects of a highly selective oxytocin antagonist (oxytocin increases the receptivity of females)
• The neural correlates of maternal and romantic love (Full study on similarities in brain between romantic and maternal love - mentions "limbic touch" - how skin-to-skin and stroking speak directly to the limbic brain and create bonding)
• Social Interaction Deficits Caused by Chronic Phencyclidine Administration are Reversed by Oxytocin (oxytocin improves social interaction deficits)
• Developmental exposure to oxytocin facilitates partner preferences in male prairie voles (Microtus ochrogaster)(oxytocin as infant affects bonding as adult)
• Peripheral Pulses Of Oxytocin Increase Partner Preferences In Female, But Not Male, Prairie Voles (oxytocin administered peripherally in pulses can activate central oxytocin in females)
• Preliminary research on plasma oxytocin in normal cycling women: investigating emotion and interpersonal distress (Relationships affect oxytocin levels and response. Women in harmonious relationships had best response.)
• Selective amnesic effects of oxytocin on human memory (oxytocin may impair memory in a way that promotes mating)
• Brain Oxytocin Correlates with Maternal Aggression: Link to Anxiety (elevated oxytocin associated with anxiety and maternal aggression toward intruders)

Nerve Growth Factor

• RAISED PLASMA NERVE GROWTH FACTOR LEVELS ASSOCIATED WITH EARLY-STAGE ROMANTIC LOVE (NGF correlates with "in love" feelings)
• NGF is released into plasma during human pregnancy: an oxytocin-mediated response? (NGF correlates with oxytocin levels)

Serotonin

ALTERATION OF THE PLATELET SEROTONIN TRANSPORTER IN ROMANTIC LOVE

Marazziti D, Akiskal HS, Rossi A, Cassano GB.

Psychol Med. 1999 May;29(3):741-5.

Comment in: Psychol Med. 2000 Jan;30(1):241-2 PMID: 10722194.

Dipartmento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, University of Pisa, Italy.

BACKGROUND: The evolutionary consequences of love are so important that there must be some long-established biological process regulating it. Recent findings suggest that the serotonin (5-HT) transporter might be linked to both neuroticism and sexual behaviour as well as to obsessive-compulsive disorder (OCD). The similarities between an overvalued idea, such as that typical of subjects in the early phase of a love relationship, and obsession, prompted us to explore the possibility that the two conditions might share alterations at the level of the 5-HT transporter. METHODS: Twenty subjects who had recently (within the previous 6 months) fallen in love, 20 unmedicated OCD patients and 20 normal controls, were included in the study. The 5-HT transporter was evaluated with the specific binding of 3H-paroxetine (3H-Par) to platelet membranes. RESULTS: The results showed that the density of 3H-Par binding sites was significantly lower in subjects who had recently fallen in love and in OCD patients than in controls. DISCUSSION: The main finding of the present study is that subjects who were in the early romantic phase of a love relationship were not different from OCD patients in terms of the density of the platelet 5-HT transporter, which proved to be significantly lower than in the normal controls. This would suggest common neurochemical changes involving the 5-HT system, linked to psychological dimensions shared by the two conditions, perhaps at an ideational level.
(Serotonin levels in those in new romances drop to levels comparable to those with obsessive-compulive disorder)

Dopamine

• Opposing Regulation of Pair Bond Formation by cAMP
  Signaling within the Nucleus Accumbens Shell (DOPAMINE INCREASE IN MATING IS MODEST, BUT TARGETS D2s, while not activating low affinity D1-like receptors)
• Dopamine oxytocin interactions in penile erection (1) SHOWS THAT OXYTOCIN PRODUCING CELLS CONTAIN DOPAMINE RECEPTORS. SO DOPAMINE CAUSES INCREASE IN OXYTOCIN.
  2) FOR ERECTIONS, DIFFERENT DOPAMINE RECEPTORS ARE ACTIVATED (WITH DIFFERENT OXYTOCIN PRODUCING REGIONS) DEPENDING ON WHETHER A RECEPTIVE FEMALE IS PRESENT OR NOT. COULD MEAN THAT SELF STIMULATION DIFFERS FROM PARTNER STIMULATION – IN WHAT OXYTOCIN REGIONS ARE ACTIVATED.)
• Nucleus accumbens dopamine differentially mediates the formation and maintenance of monogamous pair bonds (different dopamine receptors play different roles in pair bonding; activation of D2 receptors causes attraction to mate, activation of D1 receptors causes aggression toward strange potential mates)
• Addiction mechanism regulates bonding in monogamous animals (dopamine system of the nucleus accumbens produces the rewarding and sometimes addictive effects of sex, food and drugs of abuse)
• Romantic love: an fMRI study of a neural mechanism for mate choice. (Activation specific to the beloved occurred in the right ventral tegmental area and right caudate nucleus, dopamine-rich areas of the brain associated with mammalian reward and motivation.)
• Dopamine, Oxytocin, and Vasopressin Receptor Binding in the Medial Prefrontal Cortex of Monogamous and Promiscuous Voles (oxytocin, dopamine and vasopressin play important roles in mating)
• Nucleus accumbens oxytocin and dopamine interact to regulate pair bond formation in female prairie voles (dopamine and oxytocin in reward center necessary for pair-bond formation in voles)
• Dopamine D2 receptors in the nucleus accumbens are important for social attachment in female prairie voles (Microtus ochrogaster). (dopamine also plays a role in attachment in voles)
• A critical role for nucleus accumbens dopamine in partner-preference formation in male prairie voles (dopamine necessary for pair-bond formation in voles)
• Glucocorticoid receptor involvement in pair bonding in female prairie voles: The effects of acute blockade and interactions with central dopamine reward systems (dopamine critical for pair-bond formation, but cortisol, or stress, reduces bonding)
• Subjective Experiences During Dopamine Depletion (dopamine drop in healthy man causes stressed behavior that could easily interfere with capacity to bond if projected onto partner)

Vasopressin (in some ways a male counterpart to oxytocin)

• Vasopressin Stimulates Ventromedial Hypothalamic Neurons via oxytocin Receptors in oxytocin Gene Knockout Male and Female Mice (binds to oxytocin receptors?)
• Neuroendocrine bases of monogamy (oxytocin and vasopressin are the basis of monogamy)
• Oxytocin may mediate the benefits of positive social interaction and emotions (oxytocin is the basis of the positive health benefits of social interactions, alternative therapies, group support)
• Voles and vasopressin: a review of molecular, cellular, and behavioral studies of pair bonding and paternal behaviors (vasopressin induces pair bonding and male parental care)
• Oxytocin, vasopressin, and the neuroendocrine basis of pair bond formation (vasopressin involved in pair bonding)
• Is social attachment an addictive disorder? (vasopressin and oxytocin necessary for pair-bond formation in voles)
• The effects of oxytocin and vasopressin on partner preferences in male and female prairie voles (Microtus ochrogaster) (vasopressin and oxytocin necessary for pair-bond formation in voles)
• Subjective Experiences During Dopamine Depletion (drop in dopamine in healthy human male causes stressed behavior, which would likely interfere with bonding)
• The prairie vole (Microtus ochrogaster): an animal model for behavioral neuroendocrine research on pair bonding(review of how manipulations of vasopressin, oxytocin, dopamine, and corticosterone systems affect pair bond formation)
• The effects of peptides on partner preference formation are predicted by habitat in prairie voles (Oxytocin facilitated partner preference in females, but not males. Vasopressin necessary for males.)
• Facilitation of affiliation and pair-bond formation by vasopressin receptor gene transfer into the ventral forebrain of a monogamous vole (genetic engineering of monogamy through vasopressin receptor)
• Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles (Oxytocin and vasopressin involved in parenting. Oxytocin and vasopressin may affect each other’s receptors.)
• Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene (Male voles require vasopressin and dopamine activation to bond. Single gene may be responsible for male bonding behavior.)

Amygdala

• Deactivation Of The Amygdala During Human Male Sexual Behavior (neuronal activity in the amygdala decreases during sexual behavior, causing a lower level of vigilance)

Pheromones

• Lesions of the vomeronasal organ disrupt mating-induced pair bonding in female prairie voles (Microtus ochrogaster) (pheromones important for pair bonding)

Neurobiology of Pair Bonding/Attraction/Attachment

Good review of prevalence of pair-bonding in humans - not neurobiology, though

• The Evolution of Coupling (Coupling isn't just a cultural phenomenon.)
• The relative health benefits of different sexual activities (A wide range of better psychological and physiological health indices are associated specifically with penile-vaginal intercourse. Other sexual activities have weaker, no, or (in the cases of masturbation and anal intercourse) inverse associations with health indices.) Discussion: http://www.reuniting.info/node/4811
• Satisfaction sexual life, relationship, and mental health, is associated directly with penile vaginal intercourse, but inversely with other sexual behavior frequencies (Some sex therapists and educators assume that many sexual behaviors provide comparable sexual satisfaction. PVI frequency, rather than other sexual activities, is associated with sexual satisfaction, health, and well-being. Inverse associations between satisfaction and masturbation are not due simply to insufficient PVI.)
• Body mass index but not pulse pressure is associated with lesser penile-vaginal intercourse frequency in healthy young men (increasing body mass index (a rough proxy for body fat) is associated with reduced frequency of specifically penile-vaginal intercourse)
• Pavlovian Conditioning of Sexual Interests in Human Males (increasing body mass index (shows both conditioning (to more intense stimuli, and habituation) FULL STUDY AVAILABLE AT LINK
• Dopamine oxytocin interactions in penile erection (1) SHOWS THAT OXYTOCIN PRODUCING CELLS CONTAIN DOPAMINE RECEPTORS. SO DOPAMINE CAUSES INCREASE IN OXYTOCIN.
  2) FOR ERECTIONS, DIFFERENT DOPAMINE RECEPTORS ARE ACTIVATED (WITH DIFFERENT OXYTOCIN PRODUCING REGIONS) DEPENDING ON WHETHER A RECEPTIVE FEMALE IS PRESENT OR NOT. COULD MEAN THAT SELF STIMULATION DIFFERS FROM PARTNER STIMULATION – IN WHAT OXYTOCIN REGIONS ARE ACTIVATED.)
• Lending a hand: Social regulation of the neural response to threat. (Effect of husband's hand holding on threatened wife.)
• Variation in Oxytocin is Related to Variation in Affiliative Behavior in Monogamous, Pairbonded Tamarins. (Basal urinary oxytocin levels varied ten-fold across pairs and pair-mates displayed similar oxytocin levels. Affiliative behavior (contact, grooming, sex) also varied greatly across the sample and explained more than half the variance in pair oxytocin levels.)
• Close Partner as Sculptor of the Ideal Self (Benefits of having a partner)
• Neural correlates of pairbonding in a monogamous primate (basic similarities between rodents and primates in the formation and maintenance of selective social bonds. "Several studies have shown that pair-bonding involves re-organization of some brain regions (Bamshad et al., 1993; Wang et al., 1994), most notably in portions of the mesolimbic dopamine pathway.")
• The neurobiology of attraction (general speculations on the attraction process)
• Romantic Love A Mammalian Brain System For Mate Choice (brain system for mate choice overlaps with maternal circuitry)
• The neural basis of love as a subliminal prime an event related functional magnetic resonance imaging study (love involves a specific neural network that surpasses a dopaminergic-motivation system)
• The neural correlates of maternal and romantic love (human attachment employs a push-pull mechanism that deactivates networks used for critical social assessment and negative emotions, while it bonds individuals through the involvement of the reward circuitry)

Masturbation

• Autoeroticism, Mental Health, and Organic Disturbances in Patients with Erectile Dysfunction (Masturbation among ED patients has various effects, somewhat consistent with Coolidge Effect and other Cupid theories)

  See also "post-orgasmic hangover" for effects of masturbation on women.

More Research

• Limbic system and reward center
• Post-coital hangover
• Potential health benefits
• Potential health risks
• Return to detailed outline of all research

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