Motivation and emotion/Book/2018/Dopamine and love
What is the role of dopamine in the neurobiology of love?
Love has been a topic of interest since the beginning of humankind and has accordingly inspired many artworks, pieces of literature, music pieces and people alike (De Boer, Van Buel & Ter Horst, 2012). Love produces exciting, happy and rewarding feelings which are brought about by a mixture of endocrine factors, one of those being dopamine (De Boer et al., 2012). The evolutionary perspective states that love is simply a way to keep two mating pairs together to ensure the continuation of one's genes and nothing more (Seshadri, 2016). On a wider scale dopamine is thought of as the pleasure chemical of the brain involved in the reward process (Chakravarthy, Balasubramani, Mandali, Jahanshahi, & Moustafa, 2018; Martins, Mehta & Prata, 2017). Dopaminergic neurons react and fire when encountering reward like stimuli (Chakravarthy et al., 2018). This stimuli can be ether primary, such as candy or money, or more abstract, such as an attractive face (Chakravarthy et al., 2018). Psychostimulant drugs are hypothesised to work by amplifying the already present effects of the dopamine reward system (Schultz, 2002).
The dopamine system consists of four major pathways, being the nigrostriatal, mesolimbic, mesocortical and the tuberofundibular pathways (Chakravarthy et al., 2018). The nigrostriatal pathway originates from the substantia nigra pars compacta of the basal ganglia, the mesolimbic and mesocortical pathways begin in the ventral tegmental area, and the tuberofundibular pathway comes from the arcuate nucleus of the hypothalamus (Chakravarthy et al., 2018). There are also two major families of dopamine receptors that are made up of at least 5 different types of receptors (Chakravarthy et al., 2018). The D1-like family is made up of D1 and D5 receptors and the D2-like family is made up of D2, D3 and D4 receptors (Chakravarthy et al., 2018). Usually neurons will express one type of receptor from one of the families however they do occasionally mix and match (Chakravarthy et al., 2018).
There are many theories on the nature of the relationship between love and dopamine (Al-Shawaf, Conroy-Beam, Asao & Buss, 2016; Deonna & Teroni, 2016; Fehr & Stern, 1970; Reisenzein, 2017; Seshadri, 2016). This chapter will examine some of these as well as how dopamine works, its role in love and what theoretical frameworks of emotion this fits in with.
Dopamine's role in love
Dopamine's role in love is yet to be fully understood (Martins et al., 2017). It is known to have an active role in reward processing that in turn plays a major part in the complicated process of creating feelings of love (Martins et al., 2017). This occurs through interactions between many different endocrine factors and brain regions (De Boer et al., 2012; Feldman, 2017).
Human social attachments promote homeostasis, health, well-being and happiness throughout one's life, so it is no wonder people seek out love (Feldman, 2017).
Dopamine and reward processing
Dopamine is known to have a major and active role in the reward process of the brain yet its exact functions are still under investigation (Martins et al., 2017). It is believed that dopamine is involved in incentive salience and reward learning among other operations relating to reward processing (Martins et al., 2017). Dopamine has also been found to be mostly involved in the "wanting" part of a reward that leads people to investigate and yearn for a specific rewarding stimulus as opposed to the "liking" role it was originally thought to be responsible for (Martins et al., 2017). The mesolimbic dopaminergic pathway that leads to areas of the brain such as the nucleus accumbens (NA), neostriatum and the prefrontal cortex is believed to be the main pathway involved in the dopamine related reward processing procedure (Berridge & Robinson, 1998). Some also believe that dopamine can lead to prediction errors when the predicted reward of a stimuli differs from the actual reward received (Martins et al., 2017).
Berridge and Robinson (1998) conducted a study investigating the effects of dopamine depletion in rats. The rats were depleted of up to 99% of their dopamine levels (Berridge & Robinson, 1998). Their taste reactivity was then recorded to measure affective reactions to food in order to test their capacity for normal affect, taste aversion conditioning, and positive reactions to stimuli despite the absence of dopamine (Berridge & Robinson, 1998). Berridge and Robinson (1998) found that even though the ratsdopamine levels were almost completely extinguished they still displayed normal affect, they could still evaluate the reward value of new stimulus and still experienced rewards from eating the food. This supports the hypothesis that dopamine could be more involved in the "wanting" as opposed to the "liking" process of rewards.
Dopamine helps to update the rewarding value of a stimulus via prediction errors (Martins et al., 2017). This process leads to reinforcement learning (Martins et al., 2017). When someone encounters an unexpected reward elicited, for example by food or water, they experience a positive prediction error (Martins et al., 2017). This refers to when the reward for a stimulus is greater than expected leading to a larger firing of dopamine and in turn an increased appeal to said reward in the future (Martins et al., 2017). When a reward is exactly as one had expected, the null prediction error occurs, this is when no firing occurs and the salience of said reward stays stable (Martins et al., 2017). The negative prediction error occurs when the rewards of a stimulus are not as great as expected, leading to a depression in firing of dopamine and a lessened appeal to the stimulus in the future (Martins et al., 2017). The exact value of any reward is subjective and may differ from person to person (Martins et al., 2017).
Brain activity in love
Functional magnetic resonance imaging (fMRI) and Positron emission tomography (PET) have become common approaches to investigating the neurochemistry behind emotion (De Boer et al., 2012). fMRI and PET are therefore the primarily technologies used when studying the patterns of brain activity in those who are in love (De Boer et al., 2012). This is done to help us better understand the underlying processes involved in love (De Boer et al., 2012). Studies using these methods have found that areas such as the medial insula, anterior cingulate cortex, hippocampus, striatum, NA and the hypothalamus all show activation when someone is feeling romantic love (De Boer et al., 2012). These studies also show that oxytocin and vasopressen communicate with the dopamine system and induce the release of dopamine, in turn making love a rewarding experience for people (De Boer et al., 2012).The dopamine released by this interaction also acts as a general stimulant in reward related situations (Feldman, 2017). Additionally, dopamine's close links with oxytocin receptors in the striatum are thought to facilitate the attachment bonds needed for romantic love (Feldman, 2017).
Another way dopamine is involved in forming attachment bonds is when the D1- and D2-type neurons on oxytocin receptors in the NA shell work to produce maternal memory and form the repetitive patterns of caring displayed in love (Feldman, 2017). On top of this, when the D2 receptors in the NA are activated by an agonist it has been found to facilitate partner preference, allowing for people to prefer their current spouse above other possible partners (De Boer et al., 2012). In relation to this, moderate levels of dopamine in the NA promotes pair bonding whereas high doses do not (De Boer et al., 2012). D1 receptor activation in the NA has been shown to have the opposite effect by preventing partner preference, or preventing one from favouring one spouse (De Boer et al., 2012). All of these interactions between oxytocin (OT), arginine vassopressin (AVP) and dopamine seem to be the root cause for monogamy in romantic relationships (Seshadri, 2016).
These romantic relationships are said to also begin when sex triggers AVP and OT activity which in turn prompts dopamine release in the reward areas already described causing feelings of love (Seshadri, 2016). This leads a person to prefer their current mating partner and is believed to begin the pair bonding process (Seshadri, 2016). Furthermore, these patterns of brain activity found to be involved in romantic love are largely the same as those observed in maternal love (De Boer et al., 2012). This could be due to the fact that personal romantic love attachment styles are said to emerge from the initial infant-caregiver relationship (Leonti & Casu, 2018).
Prairie voles are small animals that typically live in the grasslands of the central United States (Seshadri, 2016). Studies on these animals are a main source of what we have come to know about the neurology of love as they are a monogamous species (Seshadri, 2016). After a pair bonds they will live together till death and will not re-couple when one dies (Seshadri, 2016). The male prairie vole is highly paternal and, while they are not a violent species, a paired male will show heightened aggression towards strange males (Seshadri, 2016). In these animals dopamine has been shown to regulate social and sexual behaviour, aggression and maternal care (Seshadri, 2016). Additionally sexual activity seems to be an integral part of pair bonding as it seemingly acts to reinforce the pairsrelationship (Seshadri, 2016). It is hypothesised to do this by causing dopamine release in the prairie vole's reward regions and in turn cause them to prefer their current mating partner, similar to it's effects in humans (Seshadri, 2016).
Gender differences in dopamine activity during love
There are also some gender differences in dopamine's observed effects (Seshadri, 2016). For instance, in some particularly promiscuous species the male will feel the rewards caused by the dopamine release post mating but will not correctly associate those positive feelings with the specific female (Seshadri, 2016). This causes them to not feel pair bonding or many other positive effects of love (Seshadri, 2016). Among the species that this phenomena is observed in it has also been noticed that their dopamine reward system's relationships are weaker (Seshadri, 2016). This could indicate that they fail to associate the positive feelings correctly due to too weak of a signal directing them. Having said this, this field of research is one that is yet to be properly explored, with very little information available as yet (De Boer et al., 2012).
Stages of romantic love
Romantic love is not a steady and linear process from start to finish (De Boer et al., 2012). De Boer et al. (2012) states that it has been commonly accepted that there are three stages people on the "roller coaster" that is romantic love:
- Being in love
- Passional love
- Compassionate love
Each stage has it'sown associated emotions and neurobiological background (De Boer et al., 2012).
Stage one: Being in love
Stage one of romantic love is coined "being in love" (De Boer et al., 2012). Usually people in this stage report high passion levels between them and their partner, a rapid rise in intimacy in relation to their pre-love levels and increased feelings of commitment towards their partner (De Boer et al., 2012). People are believed to stay in stage one for approximately one year (De Boer et al., 2012). As well as the high passion levels, this stage is also associated with high levels of excitement and stress caused by insecurities (De Boer et al., 2012). Positive social interactions with one another and pair bonding activities fostered by dopamine are said to help in relieving this stress (Seshadri, 2016).
Stage two: Passional love
Stage two of romantic love is "passional love" (De Boer et al., 2012). In this stage the erotic feelings of stress experienced in the first stage reduce and are replaced with feelings of safety, calm and balance (De Boer et al., 2012). This stage could be described as stable in comparison to the previous stage and typically lasts for many years (De Boer et al., 2012). In passional love passion levels remain high and intimacy and commitment levels continue to rise (De Boer et al., 2012). OT and AVP are believed to be the most active factors in this stage (De Boer et al., 2012). OT and AVP also facilitate the release of dopamine, indicating that dopamine levels are also high and very active in this stage of a romantic relationship (De Boer et al., 2012).
Stage three: Compassionate love
Stage three of romantic love is referred to as "compassionate love" (De Boer et al., 2012). Couples going through this stage often experience a decrease in their passion levels however their intimacy and commitment levels remain high (De Boer et al., 2012). Often at this stage a pair's romantic love relationship begins to resemble more of a friendship than a romantic relationship (De Boer et al., 2012). Again in this stage, similar to the one before it, OT and AVP levels are high (De Boer et al., 2012). This means that dopamine levels will likely also be high in this stage (De Boer et al., 2012). The high dopamine levels come about with the intent of maintaining and strengthening the couplespair bond (De Boer et al., 2012). Not all couples will make it to compassionate love as many split before they get the chance (De Boer et al., 2012).
Not all relationships work out in the long run, and many couples split up. This leads to the possible post-love stage of a relationship (De Boer et al., 2012). During and after a breakup people often experience high levels of stress, feelings of uncertainty about the future and feelings of grief and/or depression (De Boer et al., 2012). Having said this, these negative feelings will usually fade with time as the breakup becomes more distant history (De Boer et al., 2012).
There are many theories about how, why and when we feel emotions (Fehr & Stern, 1970). Despite this, there has been no formal decision as to which theory is the better model and no theories seem to be water tight (Fehr & Stern, 1970). The James-Lange theory, the Schachter-Singer Theory and the evolutionary perspective all have ideas on how and why love occurs that could help to better understand dopamine's role (Al-Shawaf et al., 2016; Deonna & Teroni, 2016; Fehr & Stern, 1970; Reisenzein, 2017; Seshadri, 2016).
The James-Lange theory of emotion was among the first theories to try and explain the role of physiological changes on emotions (Fehr & Stern, 1970). This theory proposes that emotion occurs due to feeling the ripple of bodily changes (such as dopamine production) in the cortex (Fehr & Stern, 1970). Therefore implying that emotions are a bottom-up process, meaning that a feeling leads to cognition (Fehr & Stern, 1970) . For example, when someone sees a spider on the floor it causes a number of inner changes which are interpreted in the brain and then cause this person to feel fear. This theory can also be applied to explain the relationship between love and dopamine. The James-Lange theory would propose that, after an exciting event such as sex, people would feel the ripples of OT and AVP activating dopamine release and then interpret this as feelings of love (De Boer et al., 2012; Feldman, 2017; Seshadri, 2016).
One common objection to this theory is that it is also possible that love and dopamine's relationship is governed by a top-down process (Deonna & Teroni, 2016). For example, we feel a warm feeling and our heart beats faster because we are feeling love (Deonna & Teroni, 2016). This theory also has the potential to explain love and dopamine's relationship, so more research is needed if we wish to end this "chicken or egg" like dispute (Deonna & Teroni, 2016).
Since the James-Lange theory, many other theories have developed that look into the effects of physiological changes on emotion (Reisenzein, 2017). One such theory is the Schachter-Singer theory that was developed with the specific purpose of improving James-Lange's (Reisenzein, 2017). This theory, similarly to the James-Lange theory, states that one first feels physiological arousal and then proceeds to identify it's reason (Reisenzein, 2017). At this point the Schachter-Singer theory forks away from the James-Lange theory in that it states that once someone has identified the reason for the physiological arousal they must then put a label on what emotion they are experiencing (Reisenzein, 2017). For example, if someone sees a spider and feels their heart beating, it is then up to them to interpret this into an emotion. In this situation it is likely most people would experience fear but if you are a person with an affinity for spiders you may think you are feeling excitement. This example also attempts to show that different people may attribute different emotions to the same type of physiological arousal depending on the context they are in, another belief of the Schachter-Singer theory (Deonna & Teroni, 2016).
This attribution clause of the Schachter-Singer theory of emotion can also help to interpret the relationship between dopamine and love. It does this by, for example, explaining why when dopamine is activated after a large, satisfying meal someone interprets that they are feeling happy, whereas after dopamine is released post sex someone may feel they are in love (Seshadri, 2016). It can also help to explain why, in more promiscuous species, males tend not to associate the dopamine reward feeling's with a specific female (Seshadri, 2016). In line with the Schachter-Singer theory, this could be due to the male not correctly labelling and attributing the positive feelings of that release of dopamine to their mating partner and rather to the physical act itself or some other exciting stimuli present at the time (Deonna & Teroni, 2016).
From the evolutionary perspective's point of view, emotions have evolved to ensure the survival and reproduction of a species (Al-Shawaf et al., 2016). They propose that love is simply used as a mechanism to form bonds between two mating partner'sand keep them monogamous in an attempt to ensure multiple healthy offspring (Seshadri, 2016). This theory goes against the James-Lange and the Schachter-Singer theories of emotion in suggesting that love may act as a motivational drive as opposed to being an emotion (Seshadri, 2016). It is possible that this theory is true yet it does not go without criticisms. For example, it does not explain why in more current times people feel love for one another yet choose not to have children, despite being capable.
Love is an inspiring and central theme for humanity (De Boer et al., 2012). This may be due to the positive feelings it elicits, partially due to the reward chemical of the brain, dopamine (De Boer et al., 2012; Martins et al., 2017). The dopamine system functions through four major pathways and two major families of receptors (Chakravarthy et al., 2018). Dopamine's role in love is yet to be fully understood but is believed to be mostly involved in the "wanting" part of reward processing (Martins et al., 2017). Studies have found that areas of the brain such as the the medial insula, anterior cingulate cortex, hippocampus, striatum, NA and the hypothalamus are involved when a person is feeling love (De Boer et al., 2012). These studies also show that oxytocin and vasopressen communicate with the dopamine system to induce the release of dopamine, in turn making love a rewarding experience for people (De Boer et al., 2012). Various exchanges between these compounds have been found to be responsible for attachment bonds, repetitive patterns of caring, partner preference and monogamy, all factors essential in romantic love relationships (De Boer et al., 2012; Feldman, 2017; Seshadri, 2016). Love is also said to begin when sex causes these compounds to communicate (Seshadri, 2016). The same patterns of brain activity are said to be involved in maternal love, most likely due to our romantic attachment styles being moulded off our initial infant-caregiver relationship (De Boer et al., 2012; Leonti & Casu, 2018). In each of the three stages of romantic love dopamine is active in some way, weather it be resolving stress through pair bonding or maintaining and strengthening that pair bond in order to keep the couple together (De Boer et al., 2012; Seshadri, 2016). The James-Lange and the Schachter-Singer theories of emotion both indicate that love is a bottom-up process that comes to be after an exciting event such as sex when people feel the ripples of dopamine's release and interpret this as feelings of love (De Boer et al., 2012; Feldman, 2017; Seshadri, 2016). The Schachter-Singer theory elaborates that this is a contextual process and that not everyone will interpret any one physiological response as the same emotion (Seshadri, 2016). Contrary to both these theories the evolutionary perspective believes that love has simply evolved to ensure the survival and reproduction of a species and go as far as to claim it may be a motivational drive instead of an emotion (Al-Shawaf et al., 2016). Whichever theory is correct, if any are completely, it is important to understand the biological side of emotions so that we can understand our own inner drives and yearnings completely (Martins et al., 2017). In saying this, a lot more research is necessary in the field before we can fully understand the comprehensive relationship between dopamine and love (Martins et al., 2017; Seshadri, 2016). In any case, love has many health and well-being benefits throughout one's lifespan, we can only hope we will all have a chance to experience them to the fullest (Feldman, 2017).
- Dopamine (Wikipedia)
- Dopamine and drug addiction (Book chapter, 2017)
- What and emotion (Book chapter, 2013)
- Neurobiology of romantic love (Book chapter, 2015)
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