A recent study conducted by researchers at the University of Maryland found that enhanced cognitive functioning and neurogenesis could be achieved through sexual experiences in rat specimens.
Aging is inevitable, and with aging comes an increasing chance of cognitive impairment. These age-associated intellectual declines, which usually appear between early adulthood and old age, are associated with the hippocampus. The hippocampus is a brain structure involved in memory formation, learning and emotions (Bear et al., 2007). Within the hippocampus is a narrow strip of cortex referred to as the dentate gyrus, which is known to have high rates of new neuron generation – or neurogenesis (Merriam-Webster, n.d). Adult neurogenesis refers to not only the process of generating new neurons but also their integration into existing brain circuitry (Scholarpedia, n.d). It has been documented that the reduction of adult neurogenesis occurs before declines in cognitive function are reported, suggesting that the reduced rate of adult neurogenesis may be contributing to the decline in cognitive function associated with aging. Thus, a reduced rate of neurogenesis in the dentate gyrus is associated with aging. It has also been documented that experience alters the rate of adult neurogenesis. In fact, there are studied that suggest rewarding experiences (such as running) actually increase the number of new neurons in the dentate gyrus. In rats, sexual behaviour activates reward centers within the brain, meaning sexual behaviour is rewarding.
Researchers at the University of Maryland examined the possibility if this sexually rewarding experience in rats could increase neurogenesis rates, therefore also enhancing cognitive functioning. Young adult (2-3 month old) male and female rats along with middle-aged (9-11 month old) retired male breeder rats were used in the experiment. Retired male breeder rats were chosen because they are much more sexually responsive than middle-aged virgin male rats. Each of the rats were permitted to engage in sexual behaviour, after which they were returned to their “home cage”. Each exposure, for every rat, was recorded and analyzed. A DNA synthesis maker called Bromodeoxyuridine (BrdU) was injected into the rats to assess the effects of sexual experience of rapid cell growth and production – or cell proliferation. The male rats were divided into groups: young and middle-aged control groups and 2 middle-aged experimental groups (continuous and discontinuous sexual behaviour). The first experimental group of male rats were (individually) exposed to a sexually receptive female once daily for 28 consecutive days to assess the effect of continuous sexual experience on adult neurogenesis. Likewise, the other experimental group of male rats were (individually) exposed to a sexually receptive female once daily for 14 consecutive days followed by a 14-day rest period to assess the effect of discontinuous sexual experience on adult neurogenesis. Additionally, to assess the effects of these continuous and discontinuous sexual experiences on hippocampal-related behaviours (i.e. memory), all rats underwent a novel object recognition test.
The results of the novel objection recognition test showed that continuous sexual experiences in middle-aged breeder rats increased cell proliferation and neurogenesis in the dentate gyrus. Continuous sexual experience rats showed improvement in their object recognition memory after completing the object recognition test; in fact, the level of improvement was similar to that of the young adult controls. These middle-aged rats spent, in comparison to the middle-aged controls, more time exploring the novel object than the familiar object. However, discontinuous sexual experience rats did not show improvement in their object recognition memory – meaning the repeated but discontinued sexual experiences did not benefit their cognitive functioning. Although the middle-age breeder controls had been exposed to a lifetime of sexual experiences, the effects of the continuous mating were not present when it was discontinued. It appears that in order to exhibit the beneficial effects in cognition, rats require stimulation through sexual experience on a regular basis; otherwise the enhanced recognition remains dormant. This is suggestive that sexual experiences may, in fact, restore the levels of adult neurogenesis in middle-aged rats to those of young adults as long as mating stimuli occurs regularly. The researchers attributed these findings to the rewarding aspect of sexual behaviour, which caused dopamine, endogenous opiates, testosterone and/or oxytocin to be released and in turn, override the negative effects of elevated glucocorticoid levels associated with the sexual behaviour. Even though this study was conducted on rats, the generalized finding of the study could pertain to the human population as well. The topic of adult neurogenesis and rewarding experiences should be investigated further, perhaps one day this study’s findings will be able to translate to humans. It would be beneficial to humans if rewarding experiences could stimulate neurogenesis as it could consequently lead to a method of preventing cognitive impairment and decline in aging populations.
References:
Adult neurogenesis. (n.d.). – Scholarpedia. Retrieved March 15, 2014, from http://www.scholarpedia.org/article/Adult_neurogenesis
Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. Philadelphia, PA: Lippincott Williams & Wilkins, 2007.
Dentate gyrus. (n.d.). Merriam-Webster. Retrieved March 15, 2014, from http://www.merriam-webster.com/medical/dentate%20gyrus
Glasper, E. R., & Gould, E. (2013). Sexual experience restores age-related decline in adult neurogenesis and hippocampal function. Hippocampus, 23(4), 303-312. Retrieved March 14, 2014, from http://onlinelibrary.wiley.com/doi/10.1002/hipo.22090/abstract?systemMessage=Wiley+Online+Library+will+be+disrupted+Saturday%2C+15+March+from+10%3A00-12%3A00+GMT+%2806%3A00-08%3A00+EDT%29+for+essential+maintenance
