How are male and female brains different?
This is a question that we are asked routinely by both men and women alike. It is unsurprising that this is such a common question, given that as neuroscience theories go, this topic always seems to be enthusiastically picked up by news-media outlets. Unlike the peer-review process for publishing scientific research, mainstream media outlets will often share the most attention-grabbing snippets of studies, even before the research has been concluded.
Consequently, the idea that there is a typical ‘male brain’ and ‘female brain’, is one of the most common myths in the neuroscience space. This idea has many iterations, a common version being that men have bigger brains than women, and that this can be extrapolated to imply something about intelligence. There are several problems with this particular idea. Moving past the initial challenge that there is no real consensus on what defines ‘intelligence’ or how best to measure it, if brain size equated to intelligence, humans would be running a slow race compared to animals like the sperm whale. Even if you look at brain-to-body ratio as a predictor of intelligence, humans would not top the list. Even between male and female humans, brain size has not been found to definitively follow gender lines. For example, studies have found many examples of women who have brains bigger than males. Further, the notion of ‘brain size’ oversimplifies the complex nature of how our brains function. Overall size doesn’t account for things like the density of connections within the brain or specific brain regions, or the speed at which those connectors are able to fire off information across our brains.
So, what are the differences between male and female brains?
This is a tricky question to answer, as studying the brain to find differences between sexes, or similarities within a single sex, is particularly difficult. One significant challenge is ‘neuroplasticity’; the ability of our brains to adapt and change based on our intentional actions, and in response to our circumstances and needs. The changes to our brains through neuroplasticity introduces variability at an individual level. Further, the structure and function of our brains, as well as our cognitive abilities, are influenced and shaped by other external factors such as age, educational background, socio-economic upbringing, and culture. Consequently, a man and a woman who grew up in the same social economic circumstances, with shared educational backgrounds, ages, and cultures, will show a more similar performance on cognitive tasks than two males or two females with differing backgrounds. As such, in order to construct a rigorous scientific study that accurately measures how brains differ across sexes, researchers must have an exceptionally large pool of participants to accommodate all these variables. If a study were somehow able to capture a group of people who shared similar backgrounds and lifestyles to account for the neuroplasticity-based changes to the brain and these external factors, the results from this niche group could not be accurately extrapolated across all humans to make broader assumptions about general differences between male and female brains.
The regions of the brain that are commonly thought to differ between men and women (when corrected for body size) are the amygdala, the hippocampus, and the corpus callosum. The amygdala is an almond-shaped structure that plays a key role in the emotional modulation of memory; the hippocampus deals with long-term memories and spatial awareness; and the corpus callosum is the region of the brain primarily connecting the left and right hemispheres. Let’s look at each of these areas in more detail.
This part of our brain is responsible for recalling the details of emotional memories, like where you were when you received particularly bad news. The amygdala is a set of structures in the brain made up of nuclei activated by the presence of strong emotions. Studies have found the amygdala to generally be bigger in men than in women, and that there are differences between the amount of sex hormones the amygdala releases in men vs. women. While previously, this part of the brain was thought to only respond to negative emotions (like fear), there is now strong evidence that shows the amygdala is activated by any powerful emotion, to help us lay down strong, vivid memories of whatever we’re experiencing. Evidence has shown that on average, women are generally better able to recall details around emotional events than men. As we know, we are able to change our brains through intentional activities and other external forces; there have been studies showing that if we use certain parts of our brain more heavily, they can become enlarged. This is relevant to the example of women being better able to remember emotional events. From a very early age women are socially conditioned to recognise and engage with their emotions and the emotions of others, while men are conditioned to supress or ignore emotions. It is not inconceivable that this could contribute to the development, ultimate structure, and functioning of the brain. As a result, it is challenging to definitely infer causation; i.e. are women better at remembering emotional events because of the innate structure of their brains? Or, are women conditioned to engage with emotions in a way that influences brain structure?
The hippocampus is most commonly associated with memory, particularly long-term memory. The hippocampus is also the ‘fact’ centre of our brains and responsible for our spatial awareness. Studies have found that on average, this region of the brain is bigger in women compared to men. There are many challenges to studying the difference in hippocampi and attributing it to a specific sex. One particular challenge is that the hippocampus reduces in size as men age. Further, research has shown that over time, different kinds of stress under different conditions affects men and women’s hippocampi differently.
As previously mentioned, intentional activities can also affect the structure and functioning of the brain, complicating studies of the hippocampus. An example of this is a study of the hippocampi in people completing the London Cab drivers’ exam. This is a notoriously difficult two-year training program that Black Cab drivers must go through to obtain a licence. To successfully complete this exam, cab drivers must learn all road names and major landmarks in central London. A study of the brains of men who had completed the two-year course and passed the exam, found an increase in the volume of their hippocampi.
This reinforces how competing factors other than gender play an important role in influencing brain development. Notably, in 2015, a large scale meta-analysis published in the journal NeuroImage found no differences in hippocampal volume between men and women.
The Corpus Callosum
Another common idea is that the brains of men and women are ‘wired differently’. The corpus callosum connects the left and right hemispheres of the brain and is often purported to show definitive differences in men and women. One study argued that women had more ‘bulbous’ corpus callosum, indicating that women were better at ‘holistic thought’ as they could more easily engage all of their brain. In 1991 another study found that while women had more ‘bulbous’ corpus callosum compared with men’s more tubular corpus callosum, that the total area was typically the same. In 1997, a meta-analysis of 49 studies of the corpus callosum found that there were no discernible differences in this part of the brain between men and women. Then in 2003, another study found that the corpus callosum in Indian men was longer than in Indian women. These wide-ranging and differing results again reinforce just how complex it is to measure and understand even a single region of the brain.
It is important to remember when interpreting scientific studies, that it is very difficult to separate them from the social context in which they were conducted. When analysing the brain, it can be challenging to know what is a result of evolution, neuroplasticity or other external circumstances. We know that intentional activities and where we focus our energy changes the structure and function of the brain. So, to ascribe causation is an incredibly complex matter. For example, with the example of the amygdala, are women in fact better at remember emotional events because of the structure of their amygdala, or has social conditioning influenced and impacted the way in which the amygdala develops over the life of a women?
While it is clear that finding differences between the brains of men and women is very complex, it is something we must keep working towards. Differences between the sexes have potential implications for how we conduct broader medical research. An example of this is the testing of medicines and diagnosing certain disorders. Overwhelmingly, studies will use male humans or animals for conducting tests. A common argument has been, particularly for the use of male animals, that it alleviates the need to account for changes due to the menstrual cycle. This decision is made based on whether there are known differences between the brains of the male and female animals. As we have demonstrated above, this is a very problematic guide, as understanding and interpreting the differences between the brains of men and women is still an evolving topic in which there is a lot of competing information. This bias towards using male patients and animals in research means that there is not the same understanding of how diagnoses and medicines may affect women differently. This undermines the ability of medical professionals to provide the same level of care for women as exists for men.
There are wide discrepancies between studies arguing there are definitive differences between male and female human brains. While we can make generalisations about the brains of men and women, these are not useful for application at the individual level. The brains of men and women are more similar than they are different, and so it’s important that we stop perpetuating the myth that ‘men are from Mars and Women are from Venus’.
This article draws on the research of Dr Indre Viskontas in Brain Myths Exploded: Lessons from Neuroscience 2017 from The Great Courses
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