Many women believe that hormone fluctuations during menstruation affect their memory, their ability to think rationally and their ability to multitask. But a new study casts doubt on the idea of so-called “period brain”.
The study, conducted by researchers at University Hospital Zurich in Switzerland, put the concept of period brain to the test by following 68 women over two menstrual cycles, and subjecting them to a battery of cognitive tests. At various stages of their cycle, the women were asked to complete computer-based tests for memory, bias and multitasking. An analysis of the results, over both cycles, showed that changes in hormone levels (oestrogen, progesterone and testosterone) as a result of the menstrual cycle were not associated with changes in performance on any of the cognitive tests.
Case closed? Well, not quite. The link between hormones and the brain is far from straightforward. But before I get into that, a bit about how the links between hormones and brain states were first identified.
In 1995, scientists at Umea University in Sweden discovered proteins that were activated by oestrogen receptors in several areas of the brain, including in areas involved in thinking, memory and attention. Given that oestrogen was known to fluctuate considerably across the menstrual cycle, scientists now had a reason to believe there was a link between sex hormones and the brain. It was thought that this might explain why some women complain of “brain fog” and forgetfulness when they are on their period.
Unfortunately, findings in this field are often inconclusive or contradictory. For example, it has been found that oestrogen can influence aspects of cognition, such as working memory and attention, with some studies suggesting that higher levels of oestrogen can lead to poor cognitive performance, while others have suggested that high oestrogen levels are associated with improved cognitive functioning. Why these results are inconsistent is not clear. However, when the vast range of chemical systems that oestrogen interacts with in the brain are considered, it’s perhaps not surprising that the relationship between the menstrual cycle and cognition is complex.
Oestrogen helps, but only for tough tasks
One factor that may influence the relationship between the menstrual cycle and cognition is the precise demands of the task we ask participants to do in the lab. This was one conclusion my colleagues and I came to following a series of studies. In our first experiment, participants were presented with two bits of auditory information (in this case, consonant-vowel syllables such as “ba”, “ta”, or “ga”), one to the left ear and one to the right ear. The participants were asked to tell us whether they heard the left ear or the right ear more clearly.
Most participants will report that they heard the information presented to the right ear more clearly. This is because auditory information presented to the right ear has direct access to the left side of the brain, which is specialised for language processing. The results indicated that relatively naturally high levels of oestrogen resulted in participants reporting a similar amount of information from both the left and the right ear. This would suggest that both side of the brain are equally involved in language processing when oestrogen levels are high. We concluded that naturally high levels of oestrogen were associated with changes in the way the brain is organised.
We then attempted to replicate this using a different task that followed the same procedure but using real words, such as “power” and “tower”. This made the task much easier for the participants. We could not replicate the effect of the first study. We think that because participants found the task easier. We were observing a “ceiling effect” – participants performed well in the task, regardless of their oestrogen levels. As such, we concluded that the easier task might have prevented any influence of oestrogen on the brain. This suggests that oestrogen may only have an effect on cognitive abilities in more difficult tasks.
Does personality contribute?
Another factor that may complicate the relationship between hormones and cognition is the biological differences underlying personality traits. There are a number of reasons to think that this might be the case. First, oestrogen interacts with a number neurotransmitters – including serotonin, dopamine, glutamate and noradrenaline – in the brain. Second, levels of these neurotransmitters, particularly dopamine, are thought to naturally differ between different people. As these neurotransmitters (again, dopamine in particular) are known to influence cognitive functioning, it is possible that certain people may be more sensitive to the effects of oestrogen than others.
In a different study, we investigated the effect of oestrogen on memory in people with a specific set of personality traits. These traits included being easily distracted, often daydreaming and being confused when several things happen at once.
Participants completed a task designed to create false memories (memories of an event that didn’t occur). We were interested to see, given that oestrogen may influence the formation of true memories, whether oestrogen could improve (reduce) the number of false memories our participants reported. To do this, we tested participants’ memory abilities at different stages of their menstrual cycle. We also measured their oestrogen levels from their saliva.
It appeared that the effect of oestrogen on memory and cognition may differ depending on the personality of the participant. Those who scored highly on a questionnaire measuring “cognitive disorganisation” (muddled thinking) showed improvements in memory when their oestrogen levels were high. In contrast, participants with low levels of cognitive disorganisation did not show any oestrogen-related improvements in memory. Unlike the new Swiss study, this suggests that natural differences in oestrogen might influence cognition, but only in a particular group of individuals.
Scientists generally accept that the effect of hormones on the brain extends far beyond behaviour related to sexual reproduction. Recent studies suggest that the relationships between hormones, the brain and behaviour are more complex than previously thought. Although the latest study provides more clarity on the link between sex hormone and how the brain functions, it is unlikely to be the final word.