Like it or not, we all have preferences in choosing romantic partners.  Piercings, freckles, hair color, eye color, body physique – through adolescence and into adulthood, we begin to develop sexual preferences to help guide our choice in whom to talk to, whom to date, and whom to marry.  While it’s tempting to attribute these tendencies to hormonal activity, much of our mate preference is due to classical conditioning.  Much like aversion (which has already been thoroughly studied in the context of fear conditioning), sexual preferences may also be an example of classical conditioning.

Our brains change through experience, as we make associations between stimuli in the world around us.  This type of learning is referred to as classical (or Pavlovian) conditioning: a previously neutral stimulus (conditioned stimulus, or CS) becomes associated with an evoking stimulus (unconditioned stimulus, or US), such that the CS now elicits a response when encountered alone.  For example, you may have never found the smell of Calvin Klein perfume exciting before, but after meeting your significant other who wears this perfume, a walk past the Calvin Klein perfume counter is exciting!  Your brain built an association between perfume and your partner, causing you to enjoy the scent of perfume even when it’s not directly from your partner.

In an experiment by Kippin et al., a female rat is scented with an unfamiliar odor (lemon) prior to mating with a male.  Afterwards, the male rat is placed with two females, one with a familiar scent (lemon) and the other with a novel scent (almond).  Remarkably, the male rat robustly chooses the female with the familiar (conditioned) scent over the unfamiliar!  This bias wasn’t seen prior to scent pairing, meaning Kippin et al. successfully altered a male rat’s sexual preference through associative learning.

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In addition to this behavior, brain regions associated with the limbic system and hypothalamus respond to the scent presentation only after pairing it with a mate.  Specifically, c-Fos expression – a marker of neuronal activity – increased in areas including the nucleus accumbens, basolateral amygdala, and lateral hypothalamus in response to the scent associated with a mate.  Many of these brain regions are also activated by pheromones, indicating that a conditioned scent triggers a similar neural pathway as the innate response to secreted pheromones.

For humans, mating preferences are more complicated.  Associations between sights, smells, sounds, and other stimuli are repeatedly paired with hormonal or emotional changes to shape our partner preferences.  Perhaps the next time you and your best friend argue over whether a celebrity is attractive or not, you’ll know that different associative learning experiences have shaped how you view potential mates!

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Images by Jooyeun Lee.

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References:

Brom M., Ellen Laan, Walter Everaerd & Philip Spinhoven (2014). The role of conditioning, learning and dopamine in sexual behavior: A narrative review of animal and human studies, Neuroscience , 38 38-59. DOI: http://dx.doi.org/10.1016/j.neubiorev.2013.10.014

Kippin T.E. (2001). The nature of the conditioned response mediating olfactory conditioned ejaculatory preference in the male rat, Behavioural Brain Research, 122 (1) 11-24. DOI: http://dx.doi.org/10.1016/s0166-4328(01)00162-0

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