Neuroanatomy of Intimacy
Even though intimacy has been broadly defined in terms of romantic love and sexual desire, the neuroanatomy of intimacy needs further explanation in order to fully understand their neurological functions in different components within intimate relationships, which are romantic love, lust, attachment, and rejection in love. Also, known functions of the neuroanatomy involved can be applied to observations seen in people who are experiencing any of the stages in intimacy. Research analysis of these systems provide insight on the biological basis of intimacy, but the neurological aspect must be considered as well in areas that require special attention to mitigate issues in intimacy, such as violence against a beloved partner or problems with social bonding.
Pair bonding, or intense social attachment, normally initiates partner preference in sexual situations and monogamy in many mammalian species. Monogamous species generally exhibit an exclusive responsibility to each other as well as co-parenting to their offspring. Studies using monogamous prairie voles (Microtus ochrogaster) showed that forming a pair bond stimulated the mesolimbic dopaminergic pathway. In this pathway, dopamine is released from the ventral tegmental area (VTA) to the nucleus accumbens and prefrontal cortex, which then signals the ventral pallidum to complete reward processing in the pathway.
The dopamine pathway starts at the ventral tegmental area (VTA) and is routed to the nucleus accumbens and the prefrontal cortex for ultimate dopamine release that yields reward and reinforcement. This helps in feeling pleasure or enjoyment of a certain stimuli and reinforcing that positive feeling when that initial stimuli occurs again.
Two important neuropeptides that mediated pair bond formation were oxytocin and arginine vasopressin (AVP). Even though both males and females have both molecules, oxytocin was shown to be predominantly in females and vasopressin predominantly promoted pair bonding in males. Receptor specificity was shown essential for mating by activating the dopamine D2 receptors in the nucleus accumbens in both male and female prairie voles. Other locations that were also activated in the study were gender specific, such as oxytocin receptors (OTR) in the prefrontal cortex and AVP 1a receptors (V1aR) in the ventral pallidum.
The Triangular theory of love by psychologist Robert Sternberg to describe the interpersonal aspects of love.
Romantic love is described as involving an individual who pays closer attention to another individual in special ways, involving attention on traits worthy to pursue. Through functional magnetic resonance imaging (fMRI), studies have shown that the right ventral tegmental area (VTA) is stimulated when subjects are shown a picture of their beloved. As part of the reward mechanism, the VTA signals to other parts of the brain, such as the caudate nucleus to release dopamine for reward.
Neuroanatomical structures involved in romantic love are closely related to structures that are involved in motivation and emotion.
Older studies have generally attributed love to the limbic system consisting of the temporal lobes, hypothalamus, amygdala as well as the hippocampus. These functional components of the limbic system are important components of emotional processing, motivation, and memory. Specifically, current research also suggests components, such as the hypothalamus, as playing a role in romantic love because it possesses the penchant for bonding in mammals by secreting the neuropeptides, oxytocin and vasopressin. Other research has implicated nerve growth factor (NGF), a neurotrophin that is fundamental in the neuron survival and development in the nervous system, in early-stage romantic love in subjects experiencing euphoria and emotional dependency, which is often a characteristic in romantic love.
Lust, also known as libido, is defined as pursuing sexual gratification. It is primarily driven by the endocrine system, but the brain is also involved in neural processing. Specifically, the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes play primary roles in the priming for sex as well as the stress response, respectively. Because intimacy is motivated by the reward system, steroid hormones activate desire to promote partner preference and social attachment in the process of sexual union. Dopamine is then released when an individual is aroused, which associates lust as a product of the dopaminergic reward system.
However, interactions of sex and romantic love do not have the same goal orientation, which helps to confirm the difference in brain activation patterns. Contrasting with the primary goal of romantic love, copulation can occur without two individuals being in romantic love or having a monogamous bond. Sometimes, copulation might not even occur in romantic love relationships. However, it still does play a role in successful reproduction when it is supplemented with romantic love.
Rejection in love
Rejection in love is considered unrequited or unreciprocated love. Separation from a loved one can cause grief and sometimes lead to an individual expressing characteristics of depression. In a study, symptoms seen in nine women who had experienced a recent breakup suggested involvement of certain neuroanatomy. Eating, sleeping, and neuroendocrine regulation was associated with the hypothalamus, anhedonia was associated with the ventral striatum and the amygdala was associated with emotional processing in these women.
The neuroanatomy of the medial surface of the cerebral cortex are implicated in rejection in love. Regular functions of many of the anatomical structures connect rejection in love to motivation, emotions, deep thinking, and reward.
Other neuroanatomy that registered unrequited love included the cerebellum, insular cortex, anterior cingulate cortex, and prefrontal cortex. All of the areas that were activated showed decreased activity when subjects emotionally reflected about the beloved rejecter.
In contrast, another study observed significant increase in activation in the VTA as well as the nucleus accumbens. Further, those rejected in love had higher stimulation in the right nucleus accumbens and ventral putamen/pallidum compared to subjects who were in romantic in love This study ultimately showed that areas that are activated in romantic love are also activated in rejection in love. Results from this study suggest that rejected lovers have same stimulation of brain regions because they are still "in love" with their rejecters. Since romantic love follows the dopaminergic reward system, the anticipatory nature of receiving a reward as well as deciding on losses and gains in decision making, allows the neural circuitry to become adaptable. This allows the rejected to change their behavior through two stages. The first is the "protest" stage where they try to win back the rejecter. The second stage or the "rejection" stage is where they feel resignation and despair, eventually leading to continuing life without the rejecter. On the other hand, the involvement of the reward gain/loss pathways intrinsic to survival provides insight on behaviors of stalking, suicide, obsessiveness and depression.