Biological basis of love

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 and behaviors that are associated with love.

Evolutionary psychology

Evolutionary psychology has proposed several explanations for love. Human infants and children are for a very long time dependent on parental help. Love has therefore been seen as a mechanism to promote mutual parental support of children for an extended time period. Another is that sexually transmitted diseases may cause, among other effects, permanently reduced fertility, injury to the fetus, and increase risks during childbirth. This would favor exclusive long-term relationships reducing the risk of contracting an STD.[1]

From the perspective of evolutionary psychology the experiences and behaviors associated with love can be investigated in terms of how they have been shaped by human evolution.[2] For example, it has been suggested that human language has been selected during evolution as a type of "mating signal" that allows potential mates to judge reproductive fitness.[3] Miller described evolutionary psychology as a starting place for further research: "Cognitive neuroscience could try to localize courtship adaptations in the brain. Most importantly, we need much better observations concerning real-life human courtship, including the measurable aspects of courtship that influence mate choice, the reproductive (or at least sexual) consequences of individual variation in those aspects, and the social-cognitive and emotional mechanisms of falling in love." Since Darwin's time there have been similar speculations about the evolution of human interest in music also as a potential signaling system for attracting and judging the fitness of potential mates.[4] It has been suggested that the human capacity to experience love has been evolved as a signal to potential mates that the partner will be a good parent and be likely to help pass genes to future generations.[5] Biologist Jeremy Griffith defines love as 'unconditional selflessness',[6] suggesting utterly cooperative instincts developed in modern humans' ancestor, Australopithecus. Studies of bonobos (a great ape previously referred to as a pygmy chimpanzee) are frequently cited in support of a cooperative past in humans.[7]

Neurochemistry

Simplified overview of the chemical basis of love.

The conventional view in biology is that there are three major drives in love – sex drive, attachment, and partner preference.[8][9] The primary neurochemicals (neurotransmitters, sex hormones, and neuropeptides) that govern these drives are testosterone, estrogen, dopamine, oxytocin, and vasopressin.[8][10]

Central dopamine pathways mediate partner preference behavior, while vasopressin in the ventral pallidum and oxytocin in the nucleus accumbens and paraventricular hypothalamic nucleus mediate partner preference and attachment behaviors.[8][11] Sex drive is modulated primarily by activity in the mesolimbic dopamine pathway (ventral tegmental area and nucleus accumbens).[8] Trace amines (e.g., phenethylamine and tyramine) play a critical role in regulating neuronal activity in the dopaminergic pathways of the central nervous system.[12]

Testosterone and estrogen contribute to these drives by modulating activity within dopamine pathways.[8] Adequate brain levels of testosterone seem important for both human male and female sexual behavior.[13] Norepinephrine and serotonin have a less significant, contributing role through their neuromodulatory effects upon dopamine and oxytocin release in certain pathways.[8]

The chemicals triggered that are responsible for passionate love and long-term attachment love seem to be more particular to the activities in which both persons participate rather than to the nature of the specific people involved.[9] Individuals who have recently fallen in love show higher levels of cortisol.[14]

Role of the limbic system

In A General Theory of Love, three professors of psychiatry from UCSF provide an overview of the scientific theories and findings relating to the role of the limbic system in love, attachment and social bonding. They advance the hypothesis that our nervous systems are not self-contained, but rather demonstrably attuned to those around us and those with whom we are most close. This empathy, which they call limbic resonance, is a capacity which we share, along with the anatomical characteristics of the limbic areas of the brain, with all other mammals.[15] Their work builds on previous studies of the importance of physical contact and affection in social and cognitive development, such as the experiments conducted by Harry Harlow on rhesus monkeys, which first established the biological consequences of isolation.

Brain imaging

Brain scanning techniques such as functional magnetic resonance imaging have been used to investigate brain regions that seem to be involved in producing the human experience of love.[16]

In 2000, a study led by Semir Zeki and Andreas Bartels of University College London concluded that at least two areas of the brain become more active when in love. These were foci in the media insula, which the brain associates with instinct, and part of the anterior cingulate cortex, which is associated with feelings of euphoria.[17]

Ortigue et al. found that an unconscious prime of the name of a romantic partner activated similar brain regions as when subjects were consciously aware of seeing partners' faces.[18] Subliminal priming with either a beloved's name or a favorite hobby activated emotion and motivational brain regions: caudate nucleus, insula, bilateral fusiform regions, parahippocampal gyrus, right angular gyrus, occipital cortex, and cerebellum. However, the love prime evoked more activation in bilateral angular gyri and bilateral fusiform regions than the hobby prime. These regions are associated with integrating abstract representations, and the angular gyrus in particular is involved with abstract representations of the self. The authors also found a correlation (r=0.496, p=0.002) between activation of a region of the angular gyrus with a passionate-love scale measuring subjective feelings of love.[18]

Love and motivation

Conscious thoughts about a romantic partner activate brain regions related to reward and motivation. Ortigue et al. investigated whether unconscious priming by a partner's name could also affect motivation. They found that priming by either a beloved or a favorite hobby improved reaction times in identifying whether a string of letters was a word or not compared against priming by a neutral friend. The authors suggest this effect happens because a beloved's name "may call for a goal-directed state" and produce "dopaminergic-driven facilitation effects."[18]

See also

References

  1. ↑ The Handbook of Evolutionary Psychology, edited by David M. Buss, John Wiley & Sons, Inc., 2005. Chapter 14, Commitment, Love, and Mate Retention by Lorne Campbell B. and Bruce J. Ellis.
  2. ↑ "Evolutionary psychology: the emperor's new paradigm" by D. J. Buller in Trends Cogn. Sci. (2005) Volume 9 pages 277-283.
  3. ↑ The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature Archived 15 May 2007 at the Wayback Machine. by Geoffrey F. Miller in Psycoloquy (2001) 12,#8.
  4. ↑ Evolution of human music through sexual selection by G. F. Miller in N. L. Wallin, B. Merker, & S. Brown (Eds.), The origins of music, MIT Press, (2000). pp. 329-360.
  5. ↑ Sexual selection and mate choice in evolutionary psychology Archived 20 September 2011 at the Wayback Machine. (PDF) by C. Haufe in Biology and Philosophy doi:10.1007/s10539-007-9071-0
  6. ↑ Griffith J. 2011. What is Love?. In The Book of Real Answers to Everything ISBN 9781741290073. http://www.worldtransformation.com/what-is-love/
  7. ↑ Sussman, Robert W. (2004). The Origins and Nature of Sociality. Transaction Publishers. p. 432. ISBN 978-0-202-30731-2.
  8. 1 2 3 4 5 6 Fisher HE, Aron A, Brown LL (December 2006). "Romantic love: a mammalian brain system for mate choice". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 361 (1476): 2173–86. PMC 1764845 Freely accessible. PMID 17118931. doi:10.1098/rstb.2006.1938. The sex drive evolved to motivate individuals to seek a range of mating partners; attraction evolved to motivate individuals to prefer and pursue specific partners; and attachment evolved to motivate individuals to remain together long enough to complete species-specific parenting duties. These three behavioural repertoires appear to be based on brain systems that are largely distinct yet interrelated, and they interact in specific ways to orchestrate reproduction, using both hormones and monoamines. ... Animal studies indicate that elevated activity of dopaminergic pathways can stimulate a cascade of reactions, including the release of testosterone and oestrogen (Wenkstern et al. 1993; Kawashima &Takagi 1994; Ferrari & Giuliana 1995; Hull et al. 1995, 1997, 2002; Szezypka et al. 1998; Wersinger & Rissman 2000). Likewise, increasing levels of testosterone and oestrogen promote dopamine release ...This positive relationship between elevated activity of central dopamine, elevated sex steroids and elevated sexual arousal and sexual performance (Herbert 1996; Fiorino et al. 1997; Liu et al. 1998; Pfaff 2005) also occurs in humans (Walker et al. 1993; Clayton et al. 2000; Heaton 2000). ... This parental attachment system has been associated with the activity of the neuropeptides, oxytocin (OT) in the nucleus accumbens and arginine vasopressin (AVP) in the ventral pallidum ... The activities of central oxytocin and vasopressin have been associated with both partner preference and attachment behaviours, while dopaminergic pathways have been associated more specifically with partner preference.
  9. 1 2 Slater, Lauren (February 2006). "Love". National Geographic. Retrieved 19 November 2009.
  10. ↑ "The neurobiology of love" by S. Zeki in FEBS Lett. (2007) Volume 581 pages 2575-2579. doi:10.1016/j.febslet.2007.03.094 PMID 17531984
  11. ↑ McGregor IS, Callaghan PD, Hunt GE (May 2008). "From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use?". Br. J. Pharmacol. 154 (2): 358–368. PMC 2442436 Freely accessible. PMID 18475254. doi:10.1038/bjp.2008.132. Recent studies also highlight remarkable anxiolytic and prosocial effects of intranasally administered OT in humans, including increased ‘trust’, decreased amygdala activation towards fear-inducing stimuli, improved recognition of social cues and increased gaze directed towards the eye regions of others (Kirsch et al., 2005; Kosfeld et al., 2005; Domes et al., 2006; Guastella et al., 2008).
  12. ↑ Miller GM (January 2011). "The emerging role of trace amine-associated receptor 1 in the functional regulation of monoamine transporters and dopaminergic activity". J. Neurochem. 116 (2): 164–176. PMC 3005101 Freely accessible. PMID 21073468. doi:10.1111/j.1471-4159.2010.07109.x.
  13. ↑ Bancroft J (September 2005). "The endocrinology of sexual arousal". The Journal of Endocrinology. 186 (3): 411–27. PMID 16135662. doi:10.1677/joe.1.06233.
  14. ↑ Donatella Marazziti; Domenico Canale (Aug 2004). "Hormonal changes when falling in love". Psychoneuroendocrinology. 29 (7): 931–936. PMID 15177709. doi:10.1016/j.psyneuen.2003.08.006.
  15. ↑ Lewis, Thomas; Lannon, Richard; Amini, Fari (2000). A General Theory of Love. Vintage Books USA. ISBN 978-0-307-42434-1.
  16. ↑ Reward, Motivation, and Emotion Systems Associated With Early-Stage Intense Romantic Love by Arthur Aron1, Helen Fisher, Debra J. Mashek, Greg Strong, Haifang Li and Lucy L. Brown in Journal of Neurophysiology (2005) Volume 94, pages 327-337.
  17. ↑ Bartels, Andreas; Zeki, Semir (27 November 2000). "The Neural Basis of Romantic Love". NeuroReport. Lippincott Williams & Wilkins. 11 (17): 3829–3834. PMID 11117499. doi:10.1097/00001756-200011270-00046. Retrieved 27 March 2012. Lay summary – BBC News (5 July 2000).
  18. 1 2 3 S. Ortigue; F. Bianchi-Demicheli; A. F. de C. Hamilton; S. T. Grafton (Jul 2007). "The Neural Basis of Love as a Subliminal Prime: An Event-related Functional Magnetic Resonance Imaging Study". Journal of Cognitive Neuroscience. 19 (7): 1218–1230. PMID 17583996. doi:10.1162/jocn.2007.19.7.1218.
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