Neuroanatomy of intimacy

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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.

Contents

Components of intimacy and neuroanatomy

Attachment

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. [1] 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. [2]

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. Dopamine Pathways.png
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. [1] Receptor specificity was shown essential for mating by activating the dopamine D2 receptors in the nucleus accumbens in both male and female prairie voles. [1] 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. [1]

The triangular theory of love by psychologist Robert Sternberg to describe the interpersonal aspects of love Love-triangle.jpg
The triangular theory of love by psychologist Robert Sternberg to describe the interpersonal aspects of love

Romantic 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. [3] 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. [4]

Neuroanatomical structures involved in romantic love are closely related to structures that are involved in motivation and emotion. Constudoverbrain - 2.png
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. [5] 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. [6] 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. [7]

Lust

Lust, also known as libido, is defined as pursuing sexual gratification. [3] [8] 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. [9] [10] 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. [10] 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. [3] [11]

Rejection in love

Rejection in love is considered unrequited or unreciprocated love. [4] 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. [12] 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. [12]

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. Medial surface of cerebral cortex - gyri.png
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. [12] All of the areas that were activated showed decreased activity when subjects emotionally reflected about the beloved rejecter. [12]

In contrast, another study observed significant increase in activation in the VTA as well as the nucleus accumbens. [13] Further, those rejected in love had higher stimulation in the right nucleus accumbens and ventral putamen/pallidum compared to subjects who were in romantic love [13] This study ultimately showed that areas that are activated in romantic love are also activated in rejection in love. [4] Results from this study suggest that rejected lovers have same stimulation of brain regions because they are still "in love" with their rejecters. [13] 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. [13] The second stage or the "rejection" stage is where they feel resignation and despair, eventually leading to continuing life without the rejecter. [8] [13] 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. [13]

Other neurological implications of intimate brain systems

Mother–child pair bond

An attachment between a mother and child arises from behavioral changes during birth, which includes lactation. [9] Release of oxytocin is important in the birthing process for the mother–child pair bond to occur in both individuals. Lactation relies on the constant release of oxytocin for the release of milk in the breast, which strengthens the first social bond of the infant and the mother. [9]

Although this is considered another type of social attachment that activates the same reward system, maternal attachment activates different regions of the brain compared to those in partner attachment. [8] In one study, overlap of activated brain regions with romantic love was found to include the nucleus accumbens, putamen, caudate nucleus, which are important in social attachment. [8] However, the only regions that were specific to maternal love were the orbitofrontal and lateral prefrontal cortex as well as the occipital and lateral fusiform cortex. [14] Moreover, oxytocin is important between the mother and her offspring, so it is suggested that oxytocin deficiency can influence how successfully the offspring is able to form a monogamous pair bond with another individual in the future. This may provide insight on issues with formation of pair bonds as well as psychological problems from an inefficient upbringing. [10] [14]

Addictiveness

PET scans of brains that are normal in comparison to brains of an obese subject, alcoholic subject, and cocaine user. Love is suggested to simulate patterns of a cocaine user in brain activation. PET - Human Addiction.jpg
PET scans of brains that are normal in comparison to brains of an obese subject, alcoholic subject, and cocaine user. Love is suggested to simulate patterns of a cocaine user in brain activation.

Love activates the same neural circuitry as maladaptive drugs, such as cocaine. Dopaminergic reward pathways are involved to elicit a response of gaining a reward and reinforcement, thereby leading some researchers to believe that love is addictive. [8] Love and drugs of abuse stimulate similar levels of dopamine for reward and reinforcement from the VTA. [10] Actions between the two mental states are very similar with those in love experiencing excessive exhilaration, insomnia, anxiety, and loss of appetite also seen in drug users. [4] [8] [15] [16] Also, brain activity observed through single-photon emission computed tomography (SPECT) showed that dopamine release in the basal ganglia of a subject who was romantically in love appeared similar to a subject addicted to cocaine. [5] Although love is suggested to be addictive based on its neurological circuitry, it cannot be simplified as addictive because it is expressed in different ways across a wide spectrum.[ citation needed ]

Gender differences in the intimate brain

Emotional processing

The amygdala, a key player in emotional processing, is suggested different between men and women. In males, emotions are considered to be primarily directed from the right hemisphere; on the other hand, it is primarily directed from the left hemisphere in females. [17]

Many of the gyri of the brain are implicated in the emotional processing of valenced words in males and females. FrontalCapts.png
Many of the gyri of the brain are implicated in the emotional processing of valenced words in males and females.

One study that tested positively and negatively valenced words on both male and female subjects found that emotional processing was indeed gender specific. In males, positively valenced words activated the left sensorimotor cortex, angular gyrus, left hippocampus, left frontal eye field and the right cerebellum, while females had activations in the right putamen, right superior temporal gyrus, left supramarginal gyrus, left inferior frontal gyrus and the left sensorimotor cortex. By contrast, negatively valenced words stimulated greater activation in the right supramarginal gyrus in males, while greater activation in the left part of the hippocampus with negative stimuli. [18] Therefore, different brain regions in males and females could allude to differential responses emotional processing in intimate situations.

Jealousy

Induction of jealousy through emotional and sexual imagery of their partner elicited differential responses in males and females. Gender Differences in Jealousy When Looking at Actual Infidelity.png
Induction of jealousy through emotional and sexual imagery of their partner elicited differential responses in males and females.

Known as the insecure feeling of a partner in regards to losing their loved one to another, jealousy can result in extreme situations such as violence and abuse from the insecure partner to their beloved. [19] In one study, men and women were shown sentences that suggested sexual and emotional infidelity and rated the intensity of jealousy that they felt. [19]

Sexual infidelity

In males, activation of brain areas that were induced by sexual infidelity laden statements included the visual cortex, middle temporal gyrus, amygdala, hippocampus, and claustrum. In females, the visual cortex, middle frontal gyrus, thalamus, and cerebellum were activated. [19] It was found that males showed more stimulation in the amygdala in regards to sexual infidelity, while females showed greater activation in the visual cortex and thalamus. [19] The regions in the male brain provided insight on neuroanatomy associated with sexual and aggressive behavior. These regions could be studied further in increased violent cases against partners, which are commonly due to male aggression. [19]

Emotional infidelity

In males, the visual cortex, medial frontal gyrus, middle frontal gyrus, precentral gyrus, cingulate cortex, insula, hippocampus, thalamus, caudate, hypothalamus, and cerebellum were shown to be activated. [19] In females, activations in the visual cortex, medial frontal gyrus, middle frontal gyrus, angular gyrus, thalamus, and cerebellum were noted. [19] Male activations were greater in the precentral gyrus, insula, hippocampus, hypothalamus, and cerebellum, while women shower greater activations in the visual cortex, angular gyrus, and thalamus. Regions in the female brain have been implicated in detection of intention, deception, and trustworthiness of others. [19] It is ultimately suggested that the different emotional processing in males and females contributes to the different responses in issues in intimate relationships.

Related Research Articles

<span class="mw-page-title-main">Striatum</span> Nucleus in the basal ganglia of the brain

The striatum, or corpus striatum, is a nucleus in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamatergic and dopaminergic inputs from different sources; and serves as the primary input to the rest of the basal ganglia.

<span class="mw-page-title-main">Limbic system</span> Set of brain structures involved in emotion and motivation

The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.

The mesolimbic pathway, sometimes referred to as the reward pathway, is a dopaminergic pathway in the brain. The pathway connects the ventral tegmental area in the midbrain to the ventral striatum of the basal ganglia in the forebrain. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.

<span class="mw-page-title-main">Nucleus accumbens</span> Region of the basal forebrain

The nucleus accumbens is a region in the basal forebrain rostral to the preoptic area of the hypothalamus. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum. The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle. Each cerebral hemisphere has its own nucleus accumbens, which can be divided into two structures: the nucleus accumbens core and the nucleus accumbens shell. These substructures have different morphology and functions.

<span class="mw-page-title-main">Dopaminergic pathways</span> Projection neurons in the brain that synthesize and release dopamine

Dopaminergic pathways in the human brain are involved in both physiological and behavioral processes including movement, cognition, executive functions, reward, motivation, and neuroendocrine control. Each pathway is a set of projection neurons, consisting of individual dopaminergic neurons.

<span class="mw-page-title-main">Ventral tegmental area</span> Group of neurons on the floor of the midbrain

The ventral tegmental area (VTA), also known as the ventral tegmental area of Tsai, or simply ventral tegmentum, is a group of neurons located close to the midline on the floor of the midbrain. The VTA is the origin of the dopaminergic cell bodies of the mesocorticolimbic dopamine system and other dopamine pathways; it is widely implicated in the drug and natural reward circuitry of the brain. The VTA plays an important role in a number of processes, including reward cognition and orgasm, among others, as well as several psychiatric disorders. Neurons in the VTA project to numerous areas of the brain, ranging from the prefrontal cortex to the caudal brainstem and several regions in between.

<span class="mw-page-title-main">Falling in love</span> Process of developing strong feelings of attachment and love

Falling in love is the development of strong feelings of attachment and love, usually towards another person.

<span class="mw-page-title-main">Lobes of the brain</span> Parts of the cerebrum

The lobes of the brain are the major identifiable zones of the human cerebral cortex, and they comprise the surface of each hemisphere of the cerebrum. The two hemispheres are roughly symmetrical in structure, and are connected by the corpus callosum. They traditionally have been divided into four lobes, but are today considered as having six lobes each. The lobes are large areas that are anatomically distinguishable, and are also functionally distinct to some degree. Each lobe of the brain has numerous ridges, or gyri, and furrows, the sulci that constitute further subzones of the cortex. The expression "lobes of the brain" usually refers only to those of the cerebrum, not to the distinct areas of the cerebellum.

<span class="mw-page-title-main">Septal area</span> Area in the lower, posterior part of the medial surface of the frontal lobe

The septal area, consisting of the lateral septum and medial septum, is an area in the lower, posterior part of the medial surface of the frontal lobe, and refers to the nearby septum pellucidum.

<span class="mw-page-title-main">Orbitofrontal cortex</span> Region of the prefrontal cortex of the brain

The orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 12 and 13; in humans it consists of Brodmann area 10, 11 and 47.

The theory of a biological basis of love has been explored by such biological sciences as evolutionary psychology, evolutionary biology, anthropology and neuroscience. Specific chemical substances such as oxytocin are studied in the context of their roles in producing human experiences, emotions and behaviors that are associated with love.

<span class="mw-page-title-main">Reward system</span> Group of neural structures responsible for motivation and desire

The reward system is a group of neural structures responsible for incentive salience, associative learning, and positively-valenced emotions, particularly ones involving pleasure as a core component. Reward is the attractive and motivational property of a stimulus that induces appetitive behavior, also known as approach behavior, and consummatory behavior. A rewarding stimulus has been described as "any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward". In operant conditioning, rewarding stimuli function as positive reinforcers; however, the converse statement also holds true: positive reinforcers are rewarding.

The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.

The biology of obsessive–compulsive disorder (OCD) refers biologically based theories about the mechanism of OCD. Cognitive models generally fall into the category of executive dysfunction or modulatory control. Neuroanatomically, functional and structural neuroimaging studies implicate the prefrontal cortex (PFC), basal ganglia (BG), insula, and posterior cingulate cortex (PCC). Genetic and neurochemical studies implicate glutamate and monoamine neurotransmitters, especially serotonin and dopamine.

The causes of schizophrenia that underlie the development of schizophrenia, a psychiatric disorder, are complex and not clearly understood. A number of hypotheses including the dopamine hypothesis, and the glutamate hypothesis have been put forward in an attempt to explain the link between altered brain function and the symptoms and development of schizophrenia.

Definitions of sexual desire are broad and understandings of sexual desire are subjective. However, the development of various ways of measuring the construct allows for extensive research to be conducted that facilitates the investigation of influences of sexual desire. Particular differences have been observed between the sexes in terms of understanding sexual desire both with regard to one's own sexual desires, as well as what others desire sexually. These beliefs and understandings all contribute to how people behave and interact with others, particularly in terms of various types of intimate relationships.

<span class="mw-page-title-main">Parental brain</span>

Parental experience, as well as changing hormone levels during pregnancy and postpartum, cause changes in the parental brain. Displaying maternal sensitivity towards infant cues, processing those cues and being motivated to engage socially with her infant and attend to the infant's needs in any context could be described as mothering behavior and is regulated by many systems in the maternal brain. Research has shown that hormones such as oxytocin, prolactin, estradiol and progesterone are essential for the onset and the maintenance of maternal behavior in rats, and other mammals as well. Mothering behavior has also been classified within the basic drives.

<span class="mw-page-title-main">Neuroscience of sex differences</span> Characteristics of the brain that differentiate the male brain and the female brain

The neuroscience of sex differences is the study of characteristics that separate the male and female brains. Psychological sex differences are thought by some to reflect the interaction of genes, hormones, and social learning on brain development throughout the lifespan.

Addiction is a state characterized by compulsive engagement in rewarding stimuli, despite adverse consequences. The process of developing an addiction occurs through instrumental learning, which is otherwise known as operant conditioning.

References

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  2. ↑ Young, Larry J.; Murphy Young, Anne Z.; Hammock, Elizabeth A.D. (5 December 2005). "Anatomy and neurochemistry of the pair bond". The Journal of Comparative Neurology. 493 (1): 51–57. doi:10.1002/cne.20771. PMID   16255009. S2CID   20453654.
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  11. ↑ Supplemented with romantic love, Love, Relationships and More. "Sex and Intimacy blog". Sexy Crush. Retrieved 2020-10-30.{{cite web}}: CS1 maint: multiple names: authors list (link)
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  13. 1 2 3 4 5 6 Fisher, H. E.; Brown, L. L.; Aron, A.; Strong, G.; Mashek, D. (5 May 2010). "Reward, Addiction, and Emotion Regulation Systems Associated With Rejection in Love". Journal of Neurophysiology. 104 (1): 51–60. doi:10.1152/jn.00784.2009. PMID   20445032.
  14. 1 2 Bartels, Andreas; Zeki, Semir (March 2004). "The neural correlates of maternal and romantic love". NeuroImage. 21 (3): 1155–1166. doi:10.1016/j.neuroimage.2003.11.003. PMID   15006682. S2CID   15237043.
  15. ↑ Beauregard, Mario; Courtemanche, Jérôme; Paquette, Vincent; St-Pierre, Évelyne Landry (May 2009). "The neural basis of unconditional love". Psychiatry Research: Neuroimaging. 172 (2): 93–98. doi:10.1016/j.pscychresns.2008.11.003. PMID   19321316. S2CID   5810242.
  16. ↑ Young, Larry J.; Lim, Miranda M.; Gingrich, Brenden; Insel, Thomas R. (September 2001). "Cellular Mechanisms of Social Attachment". Hormones and Behavior. 40 (2): 133–138. doi:10.1006/hbeh.2001.1691. PMID   11534973. S2CID   7256393.
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  19. 1 2 3 4 5 6 7 8 Takahashi, Hidehiko; Matsuura, Masato; Yahata, Noriaki; Koeda, Michihiko; Suhara, Tetsuya; Okubo, Yoshiro (September 2006). "Men and women show distinct brain activations during imagery of sexual and emotional infidelity". NeuroImage. 32 (3): 1299–1307. doi:10.1016/j.neuroimage.2006.05.049. PMID   16829139. S2CID   40335654.
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