A rat searching for cheese in a maze is one of the more iconic images associated with psychology. Some recent research extends beyond rats’ GPS capabilities by examining their sexual activity. Yup, rodent sex; we’re going there. Previous studies established that negative stressful experiences result in increases in stress hormones and decreases in neurogenesis (i.e., the creation of new neurons or brain cells).1 This led researchers to suspect that positive stressful experiences, such as physical exercise or sex, might actually result in increases in corticosterone levels (i.e., increases in a stress hormone), but actually promote neuron growth. Or, as the authors so eloquently stated, “the emotional valence or hedonic value of the stressor may play a role in determining whether an experience will produce negative or positive effects.” Or, as we’d put it (perhaps less eloquently), if the stress is good stress then the effects will probably be good too.

To test this hypothesis, researchers examined whether sexual activity influenced rats’ neuron structure and function in the hippocampus.2 In the experiment, the researchers introduced sexually receptive female rats to male rats. Half of the male rats were allowed to have sex only once, whereas the other (lucky) half were allowed to have sex once a day for 14 days. Rats in the one-time sex group had higher stress hormone levels but more new neurons. Rats in the high frequency sex group did not have higher stress hormone levels, but still continued to show neuron growth that is consistent with increased mental agility.3

These results suggest that sexual activity, whether once or frequently, benefits rats’ brains and more frequent sex increases those benefits. Of course, rats are not human (although some humans are rats); it is unclear if sex produces the exact same benefits for people. Interestingly, nerve growth factor (NGF), a neurotrophin linked to the formation of neuron growth, is present in significantly larger quantities in the blood when people have recently fallen in love (versus when they are single or in a long-term romance); NGF is also elevated at other times when excitement and novel activities are prominent (e.g., before a skydive).4 (Coincidentally, or not, cortisol, the human bodies’ stress hormone, is also elevated in the recently love-struck.) Given the strong sex drive associated with passion, or falling in love, it’s hard to not think there may be something to these rat studies. Ultimately, exactly why such increases in NGF occur, and what function it serves, is still unclear, but you can rest assured there are plenty of willing participants ready to sign up for future studies!

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1Gould E., McEwen B., Tanapat P., Galea L., & Fuchs E. (1997). Neurogenesis in the dentate gyrus of the adult tree shrew is regulated by psychosocial stress and NMDA receptor activation. Journal of Neuroscience, 17, 2492–2498.

2Leuner, B., Glasper, E.R., & Gould, E. (2010). Sexual experience promotes adult neurogenesis in the hippocampus despite an initial elevation in stress hormones. PLoS ONE 5(7): e11597. doi:10.1371/journal.pone.0011597

3Zito, K., & Murthy, V.N. (2002) Dendritic spines. Current Biology, 12, R5.

4Emanuele, E., Politi, P., Bianchi, M., Minoretti, P., Bertona, M., & Geroldi, D. (2005). Raised plasma nerve growth factor levels associated with early-stage romantic love. Psychoneuroendocrinology, 20, 1-7.

Dr. Gary Lewandowski – Science of Relationships articles | Website/CV

Dr. Lewandowski’s research explores the role of the self in romantic relationships with a specific focus on self-expansion. He has authored dozens of publications for both academic and non-academic audiences and is a member of the Editorial Board for the Journal of Social and Personal Relationships.

Dr. Tim Loving – Science of Relationships articles | Website/CV

Dr. Loving’s research addresses the mental and physical health impact of relationship transitions (e.g., falling in love, breaking up) and the role friends and family serve as we adapt to these transitions. He is an Associate Editor of Personal Relationships and his research has been funded by the National Institute of Child Health and Human Development.