The Coolidge Effect and the sex life of a rat

John Calvin Coolidge Jr. was the 30^th United States president, holding office from 1923 to 1929. He came to prominence as the Governor of Massachusetts when he ended the 1919 Boston police strike by publicly supporting his Police Commissioner’s orders for three quarters of the police force to be sacked. Coolidge's presidency steered the US through the period of unprecedented economic growth that became known as the roaring twenties. A renowned leader whose reputation has remained strong to this day, one of Coolidge's more obscure legacies was the lending of his name to a psycho-biological phenomenon – thanks to a singularly trivial event.

The story goes that President Coolidge and his wife were being shown around a farm. For some reason they became separated, viewing different parts of the farm at different times. At the chicken yard, Mrs Coolidge observed a rooster mating very actively and asked how often this occurred. She was surprised to hear it was dozens of times a day and joked that the staff should tell the president when he came by. When the president's party later arrived, the farm staff duly recounted his wife's observations concerning the rooster. President Coolidge demonstrated a keen sharpness of mind when he asked the simple but revealing question of whether the cock was mating with the same hen every time. On hearing to the contrary the President suggested the staff might mention that to Mrs. Coolidge.

The Coolidge Effect, named after the 30^th President of the United States, is concerned not with industrial relations, economics or outstanding leadership. Rather, it concerns an aspect of sexual behaviour. Specifically speaking, it denotes the observation, which holds for many species, that males will be more eager to mate with a new female, as opposed to one that is familiar. In technical terms, males have been found to display a shorter refractory period (that is, the time between one copulating session and the next) if a new partner becomes available. The research underlying the Coolidge Effect was written up by scientists from the University of California in a paper published in 1963.

The study falls fairly and squarely in the field of experimental psychology, such that several similar scenarios were set up and different behaviours were observed, counted and compared across these different conditions. The particular behaviour under observation was rats having sex. Male rats were required to pass a simple test in order to be selected for the study. They were placed with a female on heat for half an hour and those that copulated to ejaculation a minimum of two times were chosen. Interestingly, how the researchers were able to detect the occurrence of a rat ejaculation I can scarcely imagine, and sadly the paper doesn't explain. Maybe a reader of this blog could enlighten the rest of us!

For the main experiment male rats were paired up with females on heat and allowed to mate until they stopped for at least 30 minutes, at which point they were declared to be sexually exhausted. Then the female was removed. Next, some of the males were introduced to a new on-heat female while others were re-introduced to the same on-heat female that they had reached sexual exhaustion with. Sexual activity during the re-introduction phase was measured, in particular the number of times the female was mounted and the percentage of male rats achieving first and second ejaculations.

At first nothing in the rats’ behaviour was untoward. The number of mountings and first ejaculations was similar whether or not a new female was reintroduced. However, none of the rats re-introduced to the original partner ejaculated for a second time, whereas several of the rats with new partners did enjoy what might be termed a "second coming". In addition, three male rats that were not at all interested in a re-introduced familiar female changed their tune and were seen to copulate with a new partner introduced later in an additional phase of the experiment. Final evidence for the Coolidge effect was an observation made among rats that copulated in a further re-introduction phase. When the partner was new 86% of males achieved ejaculation, a much higher proportion than the 33% managing this when the same partner was reintroduced.

So there is the evidence for the Coolidge Effect. It was based on the finding that male rats become more interested in sex with a new partner rather than an existing mate. But what does it mean? Why might it exist? It is probably easiest to understand from the perspective of evolution, that is, by considering the benefits to the continuation of the species. The evolutionary advantage of the Coolidge Effect is that it encourages a wider circle of copulation partners, so increasing the chances of pregnancy and procreation. Think of it as Nature's way of guarding against putting all your eggs in the same basket, as the old saying goes.

This paper is a worthy addition to the Cool Psychology Blog for several reasons. For one thing, it’s cool for rat ejaculations to be used as a variable in a psychology experiment. It just is. Also this would have been a fascinating experiment to run on a day-to-day basis – for instance, I wonder if any of the rats gained particular reputations for their prowess (or lack of). It's fairly well known that psychologists are fascinated by many different aspects of behaviour but who knew this stretched to an interest in rats having sex? On the other hand, you could say that the research is somewhat sexist. In the narrative only the males seem to be active participants in the mounting, copulating and ejaculating. It takes two to tango so it is likely that the females were more active than portrayed.

This line of research is still ongoing, but has grown in sophistication. A Mexican team published a Coolidge Effect paper in 2012 that measured sperm count and erection occurrence as well as the number of mounts and ejaculations. While evidence for the Coolidge Effect was apparent, still this recent paper doesn’t reflect societal trends towards sexual equality – it is still all about the males, with the female rats considered as passive sexual partners. On the other hand, a paper from the mid-1980s did show evidence of a Coolidge Effect in female hamsters re-introduced to the same or a new male partner.

The reference to the original research described in this blog that lead to the coining of the term “The Coolidge Effect” is included below. Unfortunately the article is copyright protected and so only available at libraries that pay to subscribe to it – for example university libraries. This link takes you to the paper’s official web page where you can read a short summary. 

References

Lester, G.L. & Gorzalka, B.B. (1988). Effect of novel and familiar mating partners on the duration of sexual receptivity in the female hamster. Behavioral & Neural Biology 49, 398-405.

Tlachi-Lópeza, J.L., Eguibarb, J.R., Fernández-Guastic, A. & Luciod, R.A. (2012). Copulation and ejaculation in male rats under sexual satiety and the Coolidge effect. Physiology & Behavior 106, 626–630.

Wilson, J.R., Kuehn, R.E. & Beach, F.A. (1963). Modification in the sexual behavior of male rats produced by changing the stimulus female. Journal of Comparative and Physiological Psychology 56, 636-644.

Do the summer months make us happy?

Happiness is defined by psychologists as the frequent experience of positive emotions, such as joy, interest and pride (see Lyubomirsky, King & Diener, 2005, listed below). A series of studies carried out by psychologists has assessed the popular belief that the weather can affect happiness and mood. These studies arose from everyday observations of people declaring how depressing they find the weather on a rainy day, or how uplifted they feel during a sustained spell of sunshine. Psychologists have applied a scientific approach to the investigation of how weather and mood might be related. To be scientific requires taking objective measurements of people’s mood and mapping that against an accurate record of the meteorological conditions at the time. When such an approach is taken, the relationship between weather conditions and happiness is rather a weak one.

A typical study was carried out recently by some Dutch psychologists (see Klimstra and colleagues, 2011, listed below). The happiness of over 800 volunteers was measured by having them rate three statements about their mood, e.g. “I feel content”, on a scale from “not at all” to “very much”. They did this several times over a 17 month period. For each day on which a questionnaire was completed, information was obtained from the Royal Netherlands Meteorological Institute on average temperature, hours of rainfall and hours of sunshine.

When the questionnaire responses were compared with the meteorological data, there was little correspondence between them. For half the participants, happiness was completely unaffected by sunshine, rainfall and temperature. For the other half of participants the relationships were more complicated, with some people being found to be more happy in typically summery weather, but others being found to be less happy in the same conditions. Even here, though, the relationships were not that strong with the greatest amount to which the weather influenced happiness being no more than 15%.

These findings, and similar ones from other studies, suggest that the relationship between the weather and our happiness is much less important than people think. Why might this be? One explanation is that a “focussing illusion” occurs (see Schkade & Kahneman, 1998, listed below). The illusion is such that in the depths of winter we imagine an idealised hot sunny day and focus on the differences, e.g. warmth rather than cold, and sunlight rather than cloud. In focussing on these differences we forget that a real-life hot summer day might include negative as well as positive features - such as having to go to work, child supervision, feeling too hot, and so on. Focussing on ideal examples rather than realistic ones makes us overestimate the extent to which warm sunny days will make us feel happy.

The generally held belief of a strong association between summer weather and happiness does not stand up to scientific scrutiny. Nevertheless, many people believe such a link exists, and therefore the connection between summer weather and happiness is a powerful psychological idea. The potency of such ideas should not be underestimated. After all, the placebo pill contains no drug and yet has been seen to be an effective treatment for a range of medical conditions (Eccles, 2002). A summer mind-set is likely to be a far more valuable asset in the pursuit of positive mood and happiness than summer weather itself.

References

Eccles, R. (2002). The powerful placebo in cough studies? Pulmonary Pharmacology & Therapeutics 15; 303-308.

Klimstra, T.A., Frijns, T., Keijsers, L., Denissen, J.J.A., Raaijmakers, Q.A.W., van Aken, M.A.G., Koot, H.M., van Lier, P.A.C. & Meeus, W.H.J. (2011). Come rain or come shine: Individual differences in how weather affects mood. Emotion 11, 1495-1499.

Lyubomirsky, S, King, L. & Diener, E. (2005). The benefits of frequent positive affect: Does happiness lead to success? Bulletin 131, 803-855.

Schkade, D.A. & Kahneman, D. (1998). Does living in California make people happy? A focusing illusion in judgments of life satisfaction.  Psychological Science 9, 340-346.

Is love a drug?

The heady rush of intense romantic love is, perhaps, a defining aspect of what is to be a human being. Psychologists named this feeling “limerance” in the 1970s, and by the 1980s they were measuring it using questionnaires with exciting sounding names like the “Passionate Love Scale”. Still, the 2000s arrived and several important psychological questions around the nature of romantic love still remained unanswered. Should love best be thought of as an emotion in its own right? What is the relationship between romantic love and sex? And is love really a drug, as Roxy Music suggested in their 1975 hit single?

In 2005, psychologist Arthur Aron and his colleagues decided to delve into these interesting issues. 17 young men and women who had recently fallen in love and were in a relationship responded to a newspaper advertisement. Each provided a photograph of their beloved and, to provide a point of comparison, a second photograph portraying a friend of the same age and sex. One by one, the volunteers were inserted, torpedo-like, into an fMRI machine. Magnetic resonance imaging (MRI) uses magnetization of atoms in the body to create images of the brain and other internal organs. Functional MRI (fMRI) is a further refinement that can measure changing activity over time by detecting increased amounts of oxygen in the blood.

While having their brains scanned the volunteers viewed their photographs through an angled mirror. The researchers compared the brain scan images showing parts of the brain “lighting up” for the beloveds’ photographs with the friends’ photographs. This showed which brain regions became active in response to intense romantic love, over and above friendship. The findings were intriguing.

Romantic love activated a number of well-known emotional areas of the brain, namely the caudate nucleus, ventral tegmental area, insular cortex and cingulate cortex. There was no evidence of any specialised or unique brain system for love, which tells us that love is probably not an individual emotion in its own right. Instead, romantic love is better thought of as an accumulation of motivations and emotions, described by the researchers as a “goal-directed emotional state”. In other words, love is a mind-set that causes the experience of other more fundamental emotions like euphoria. This makes sense from an evolutionary perspective; romantic love directs us towards the goal of obtaining a partner for reproductive purposes, and finding one’s partner is rewarded by feelings of extreme emotional pleasure. Having said that, next time you are smooching your lover, choose you words carefully. Whispering how intense a goal-directed emotional state they set-off in you isn’t particularly romantic!

Recording activation in the caudate nucleus and ventral tegmental areas of the brain is interesting because these are key parts of the brain’s reward pathways. These pathways respond to pleasurable stimuli like eating chocolate, receiving money or experiencing an intense “high” from drugs like cocaine. The objective demonstration of activation of the brain’s same reward pathways by romantic love and drugs provides a scientific backing for the poetic idea of love being a very potent drug. Bryan Ferry was right!

And what of the age-old question of the relationship between love and sex? On the whole, the brain areas activated by romantic love were different to those activated during sexual arousal. We know this thanks to a 2002 study of 14 young men asked to watch an erotic video while undergoing an fMRI scan. At the same time, a strategically positioned electrical “cuff” verified physical signs of sexual arousal. The brain areas activated were the visual areas, the insula, the temporal and cingulate gyri, the caudate and the putamen. Because the brain regions activated for romantic love and sexual arousal were different, this shows that love and sex are distinct entities. More profoundly, the findings provide a scientific validation for the feeling of sexual desire in the absence of romantic love, otherwise known as “lust”. 

Rarely does one scientific study shine a light on so many quintessential issues. The patterns of brain activation in lovers viewing pictures of their darlings validate the lyrical concept of love being like a drug. In so doing, they underline the powerful hold romantic love can exert on people. Considering love as apart from lust informs how, as people age and sexual activity lessens, fulfilling long-term romantic relationships still evolve and thrive. Coming to think of romantic love not as one single emotion but as an accumulation of motivations and emotions provides insights into the complexity of love and hints at why humans remain inherently fascinated by it. This fascination is reflected in the portrayal of romantic love in music and the arts since time immemorial. And now, at last, science has joined the party.

The reference to the full paper describing this study is included below. If you access it from a library that subscribes to the journal you will be able to download the pdf file containing the article for free. If not, the link contains an e-mail address for one of the authors, Lucy L Brown. If you contact Dr Brown and ask very politely I’m sure she would send you a pdf copy of the paper for free.

Arthur Aron, Helen Fisher, Debra J. Mashek, Greg Strong, Haifang Li and Lucy L. Brown (2005). Reward, Motivation, and Emotion Systems Associated With Early-Stage Intense Romantic Love. Journal of Neurophysiology 94, 327-337. Link.