Romantic Love: the Physiochemical Construct by Neurotransmitter Activity

love1Attachment, commitment, intimacy, passion, and jealousy are a few emotions used to understand and explain the psychological construct of love [1]. Until recently, these emotional states appeared to be a hypothetical assembly without scientific investigations in their neurobiological basis. Dr. Helen Fisher revolutionized the concept of brain in love by elaborating on the three stages of love and the congruent evolution of the brain. According to Dr. Fischer, romantic ardor is a universal experience, deeply embedded in the brain [2]. Today, our knowledge on the neurobiology of love has expanded while the “ingredients” of the ardor, as expressed in Shakespeare’s early sonnets, are better defined.

Love involves having both an emotional bond to someone, as well as having sensory stimulation that one desires [3]. Hence, it was speculated that the respective neural circuits involved might be shared with the neural pathways controlling reward, pleasure, appetitive and addictive behaviours [4]. Different neural pathways, with different neurotransmitters, control the three main stages of “falling in love” as elaborated by Dr. Fischer – lust, attraction, and attachment [2]. Romantic ardor is a universal experience, deeply embedded in the brain [2]. Today, our knowledge on the neurobiology of love has expanded while the “ingredients” of the ardor, as expressed in Shakespeare’s early sonnets, are better defined.

Shakespeare’s allusion to “love at first sight” or “lust” is controlled by the production of sex hormones, testosterone, and estrogen, in contrast to the later stages driven by neurotransmitters. While estrogen plays a role only in females, testosterone plays a critical role in the sex drive of males and females alike [5]. Men in love report lower testosterone levels, whereas women produce more testosterone, with the implication that falling in love may induce temporary physiological and behavioural changes eliminating fundamental biological differences between the sexes [6]. This is exemplified by the aggressive sexual possessiveness due to the stimulation of testosterone receptors in hypothalamic regions, resulting in conversion of testosterone into estrogen, which cause an increase in aggressiveness [7]. Indirectly, testosterone also stimulates production of vasopressin in the medial amygdala, lateral hypothalamus, and the preoptical medial area, regions involved in aggressive behaviours [7].

All days are nights to see till I see thee,
And nights bright days when dreams do show thee me [8].

Shakespeare characterizes the second phase, termed as “attraction”, wherein partners spend a majority of their time and resources with each other or are in each other’s thoughts. Loss of appetite and sleep, along with daydreaming about their new lover are common indicators of attraction [5]. Attraction may be attributed to the work of a group of neuro-transmitters called monoamines such as adrenaline, dopamine and serotonin. Adrenaline, a neurotransmitter of the stress response circuit, is activated during the initial stages of love [5]. It is responsible for the sweating, nervousness, heart racing and dryness of mouth in the proximity of your lover [5]. In MRI scan examinations on newly ‘love struck’ couples, it was reported that they had high levels of the neurotransmitter dopamine, which stimulates desire and reward pathways and produces a sensation of extreme pleasure [2]. Dr. Fisher suggests “couples often show the signs of surging dopamine: increased energy, less need for sleep or food, focused attention and exquisite delight in smallest details of this novel relationship” [2]. Furthermore, individuals who are currently in love also revealed lower levels of serotonin, as observed in patients suffering compulsive-obsessive disorders [9]. Paradoxically, serotonin enhances positive mood and is often termed as a pleasure hormone; however, it also drives mental calmness, which is detrimental to attractive social behaviours [5]. Furthermore, serotonin is responsible for the vain efforts of focusing our thoughts due to continuous interruption by the thoughts of your lover [5]. Thus, attraction is characterized as a “roller-coaster of emotions,” with fluctuations in the autonomic nervous system and related neuropeptides in a short period of time.

So long as men can breathe or eyes can see,
So long lives this and this gives life to thee [8].

Shakespeare then portrays the attachment phase, or “long-lasting love,” which is defined by a sense of calm and security. Researchers speculate that oxytocin and vasopressin influence this final stage. Oxytocin, a critical neurotransmitter in love physiology, is responsible for stress reduction by inhibiting the release of corticoids. Literature has also shown that oxytocin positively influences pair bonding and other forms of social attachment [1]. Vasopressin is the second neurotransmitter involved in the long-term commitment stage [5]. When male prairie voles were injected with vasopressin antagonists, the pair bond with their partner deteriorated and a loss of devotion to their partners was reported as they made few attempts to repel the approach of novel partners [5]. Furthermore, male prairie voles that were given neonatal injections of vasopressin exhibited more aggression towards novel males and females after pain-bonding with their partner [1]. Thus, vasopressin and oxytocin demonstrate a relationship between physiological “love-signaling” and subsequent social or protective behaviors.

Love as a complex neurobiological phenomenon relies on brain reward activity, which involves oxytocin, vasopressin, dopamine, and serotoninergic signaling. The early phases of love are distinct from later stages both behaviorally and neurologically. Furthermore, this neurological basis of love draws connections between physiological aspects related to romantic love [5]. Love, pleasure, and lust induce lower stress levels and, consequently, improve healthy life-style and relationships [5]. There may be many implications of this shared neural circuitry on mind-body integrative medicine, an area of research being explored.

Thus continues the saga of understanding love, the emotional construct that immortalizes Shakespeare’s sonnets and the physiochemical result of neurotransmitters’ interplay in the nervous system.   

References

1. Carter C.S. “Neuroendocrine perspectives on social attachment and love.”          Psychoneuroendocrinology 23 (1998): 779-818.
2. Fisher, H. “Helen Fisher: The brain in love.” Presentation at TED (Technology, Entertainment,            Design) Conference at Monterey, CA, February 27-March 1, 2008.
3. Komisaruk B.R. and B. Whipple. “Love as sensory stimulation: physiological consequences     of its deprivation and expression.” Psychoneuroendocrinology 23 (1998): 927-944.
4. Esch T. and G.B. Stefano. “The neurobiology of pleasure, reward processes, addiction and        their health implications.” Neuroendocrinology Letters 25 (2004): 235-251.
5. Esch, T. and George B. Stefano. “The neurobiology of love.” Neuroendocrinology Letters 26, no. 3 (2005): 175-192.
6. Marazziti D. and D. Canale. “Hormonal changes when falling in love.”    Psychoneuroendocrinology 29 (2004): 931-936.
7. Giammanco, M., G. Tabacchi, S. Giammanco, D. Di Majo, and M. La Guardia. “Testosterone and aggressiveness.” Medical Science Monitor 11 (2005): RA136-RA145.
8. Shakespeare, W. The Sonnets. Edited by G. Blakemore Evans. London: Cambridge University Press, 1996
9. Marazziti D., and G.B. Cassano. “The neurobiology of attraction.” Journal of Endocrinology   Investigation 26 (2003): 58-60.

Image Credits: Nevit Delmen. “Brain gears by love.” Wikipedia Commons, July 2011. http://commons.wikimedia.org/wiki/File:Mr_Pipo_Brain_Gears_by_Love.svg (accessed 24th October 2013).
“Brain love and tear drops: the science of emotion.” Illustrated in Binary This blog, February 2012. http://binarythis.com/2012/02/23/brain-love-and-tear-drops/ (accessed 24th October 2013).

Hely Shah is an undergraduate student in faculty of Science at the University of Calgary majoring in Neuroscience. She is an undergraduate student researcher in Dr. Kirton’s lab at the Alberta Children’s Hospital through the Calgary Paediatric Stroke Program.  Follow The Triple Helix Online on Twitter and join us on Facebook.

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