A recent study from Concordia University lead by Professor Wayne Brake has shown that high levels of estrogen in female rats interfere with their learning of previously encountered stimuli.
The study confirms recent findings that high levels of a major female sex hormone, called estradiol, interfere with latent inhibition. Latent inhibition is a kind of “hidden” learning that results in decreased performance on tasks.
Brake’s study is a follow-up to a previous study in which estrogen was experimentally manipulated by removing the ovaries, replacing them with low or high doses of estrogen. Interestingly, both studies yielded the exact same results.
This study is the first to show that the interference of estrogen is based in the activational and not organizational actions of hormones. As U of T’s Gillian Einstein explains in her book, Sex and the Brain, the cornerstone in the field of hormones and behaviour is the organizational and activational hypothesis. This is the idea that the organization of hormones early in development forms a circuit that is later activated at puberty. Fro example, these circuits set up the behaviour of “mounting” and “lordosis,” in which a male rat will mount onto a female after she performs the receptive cue of arching her back.
Another key idea when thinking about estrogen is that its influence can either be beneficial, such as in memory and aging, or negative in that it can cause cancer. In response to the results of Brake’s study, Professor Einstein explains that “the picture is a lot more subtle for [estradiol].”
In other words, we don’t know whether the effects of estradiol on learning are “negative to behaviour, or positive to behaviour [when] interfering with latent inhibition. That could be positive in memory or it could be negative in memory. But it’s the first [study] to show that this is based on the activation of actions of hormones,” says Einstein.
So what does this mean for human females? As it turns out, ladies and female rats are quite different. In contrast to a female human’s average 28-day menstrual cycle, female rats cycle every four to five days, meaning that rats are continuously dominated by their estrous cycle. For the people out there wondering whether female rats experience PMS symptoms the same way female humans do, the short answer is no: the two species are riddled with complexities that make them difficult to compare.
As Professor Brake explains, “It’s hard to measure what we would call PMS in rodents, simply because what goes on with them is far more outlandish — because the female now only has one thing on her mind, and that’s to reproduce.”
Both researchers stress that the effect of estrogen on mental resources involves a highly complex relationship.
When asked whether there was any task that was most likely to tax a woman’s memory resources, Professor Brake responded, “I wouldn’t even try to guess that. There are lots of cognitive tasks that people use in psychology that tax resources. Some tasks show that estrogen helps with these tasks, and sometimes it hurts.”
Brake’s study also supports the idea that estrogen affects women’s abilities to problem-solve. “An example [of estrogen influence] would be mental rotation tasks. There is a huge sex difference in mental rotation tasks, in that men are much faster at figuring out this task than women. Women are usually only worse at this task when their estrogen levels are high. When their estrogen levels are lower, they perform just as well as men. The practical application of that is if you’re the navigator on a road trip, you’re going to be better at figuring out the map when your estrogen levels are low.”
Although rats provide a decent window into human nature, it would be far too early to conclude that estrogen has either a particularly adverse or advantageous effect on female cognition. However, researchers like Brake and Einstein bring science closer to the answers, one rat at a time.
