Neuroscience explains differences between sex and gender
When it comes to mental health, we lump males and females into the same treatment programs without taking into account the differences between a male and a female brain. Perhaps now that we know the difference, better treatment outcomes can be gained if we start to look at the treatment programs taking into account the differences in brain structure between males and females.
As a caveat, in a patriarchal society, gender roles, personal identity, social media, and exposure to other mental health risk factors have adverse effects on the psychological perceptions of both men and women. This article about the differences in brain structure is written to provide treatment insights and not to be used for gender arguments.
Data on Males and Females Mental Disorders Data shows that gender correlates with certain mental disorders. Women are more likely to be diagnosed with major depression, general anxiety disorder (GAD), panic attacks, phobias, eating disorders and social anxiety disorders (SAD). Men, on the other hand, are more likely to be diagnosed with substance abuse and antisocial personality disorder. The data on depression might be skewed because research shows that men are less likely to speak about their experiences with depression and to seek treatment for depression. This data somewhat correlates with the data that more women attempt suicide and engage in self-harm while more men die from suicide. In 2019, the successful suicide rate in the US was 3.7 times higher for men than women. Men also suffer from eating disorders, but gender bias, stigma, and shame led to a serious case of under-reporting, under-diagnosed and under-treated. Clinicians are also not well-trained and lack the resources to treat men with eating disorders. Signs of men having eating disorders are muscle dysmorphia. Data also shows that there are no differences in diagnosis rates between genders for disorders like schizophrenia, bipolar and obsessive-compulsive disorders (OCD). For Post-Traumatic Stress Disorder (PTSD), the data shows that men are more at risk of PTSD due to past violent experiences such as accidents, wars and witnessing deaths. At the same time, women are more at risk of developing PTSD dues to sexual assault, rape and child sexual abuse. This indicates that besides biological factors, societal and cultural conditioning also plays a role in determining the development of different mental illnesses in men and women. In a patriarchal society, gender roles, personal identity, social media and exposure to other mental health risk factors have adverse effects on the psychological perception of both men and women.
Neuroscience of Sex Differences
Volume: In terms of structure, the average weight and size of adult male brains surpass those of females by approximately 11–12% and 10%, respectively.While statistical variances exist in the percentages of white matter and gray matter between sexes, proponents posit that the overall brain size distinction between men and women primarily influences these differences. Some argue that even after accounting for brain volume, these sex-related disparities in gray and white matter percentages persist.
Researchers have observed greater cortical thickness and complexity in females, both before and after adjusting for overall brain volume. In contrast, males exhibit greater surface area, brain volume, and fractional anisotropy, both before and after adjusting for overall brain volume. Although attributes remain greater for both genders, the overall differences in these attributes diminish after adjusting for overall brain volume, except for the increased cortical thickness in females.
Cortical complexity and features have shown some positive correlation with intelligence, leading researchers to hypothesize that these differences may have evolved in females to compensate for their smaller brain size and equalize overall cognitive abilities with males. However, the specific reasons for the environmental selection of this trait remain unknown. Further analysis of brain volume, surface area, and cortical thickness involved testing men and women separately on verbal-numerical reasoning and reaction time. Men slightly outperformed women in both tests. Subsequent examination to what extent these performance differences were mediated by various attributes of the male and female brain revealed that in verbal-numerical reasoning tests, surface area and brain volume mediated performance by more than 82% in both groups. Cortical thickness mediated performance to a lesser extent, with 7.1% and 5.4% in each group. In reaction time tests, total brain and white matter volumes mediated performance by over 27%, while other attributes mediated performance by smaller percentages (less than 15.3%), especially mean cortical thickness (mediating less than 3% of performance).
According to the neuroscience journal review series Progress in Brain Research, males possess larger and longer planum temporale and Sylvian fissure, while females exhibit significantly larger proportionate volumes to total brain volume in the superior temporal cortex, Broca's area, the hippocampus, and the caudate. Additionally, the midsagittal and fiber numbers in the anterior commissure connecting the temporal poles and the mass intermedia connecting the thalami are larger in women. Lateralization: Sex differences in brain lateralization are often discussed, with men frequently described as having a more lateralized brain, often associated with distinct "left-" and "right-" brained abilities. The higher prevalence of left-handedness in men is considered a supporting factor for the idea of sex-based differences in brain lateralization, although it remains unclear whether left-handedness directly correlates with this lateralization.
A 2014 meta-analysis examining grey matter in the brain revealed sexually dimorphic areas in both volume and density. The synthesis of these findings suggests that volume increases in males tend to occur on the left side of brain systems, whereas females generally exhibit greater volume in the right hemisphere. However, a prior meta-analysis from 2008 contradicted these findings, stating that the difference in brain lateralization between males and females was not statistically significant.
Amygdala: Behavioral variances between males and females may hint at distinctions in amygdala size or function. A 2017 review of studies on amygdala volume revealed an initial raw size difference, indicating that males possessed a 10% larger amygdala. However, this discrepancy was deemed misleading upon normalization for brain size, as there was no significant difference in amygdala size across sexes.
Regarding activation, there is no discernible difference in amygdala activation between sexes. Behavioral disparities observed in tests may stem from potential anatomical and physiological variations in the amygdala between males and females rather than differences in activation.
Emotional expression, understanding, and behavior appear to exhibit variations between males and females. A 2012 review concluded that there are differences in the processing of emotions between the two sexes. Males tend to display more robust reactions to threatening stimuli, and their responses may involve a greater inclination towards physical violence.
Hippocampus: Atrophy of the hippocampus is linked to several psychiatric disorders that exhibit a higher prevalence in females. Moreover, variations in memory skills between males and females may imply differences in hippocampal volume (HCV). A 2016 meta-analysis, initially noting a greater HCV in males without accounting for total brain size, later revealed that after adjusting for individual differences and total brain volume, no significant sex difference in HCV was observed. This result was unexpected, given the anticipation that women might have a larger hippocampus volume.
Grey Matter: In a 2014 meta-analysis where differences were examined, various distinctions in grey matter levels between the sexes were identified.
For females, the findings revealed greater grey matter volume in the right frontal pole, inferior and middle frontal gyrus, pars triangularis, planum temporale/parietal operculum, anterior cingulate gyrus, insular cortex, and Heschl's gyrus. Additionally, larger volumes were observed in both thalami and precuneus, the left parahippocampal gyrus, and lateral occipital cortex (superior division). Particularly pronounced increases in volume for females were noted in right hemisphere areas related to language, along with several limbic structures such as the right insular cortex and anterior cingulate gyrus.
Conversely, males exhibited greater grey matter volume in both amygdalae, hippocampi, anterior parahippocampal gyri, posterior cingulate gyri, precuneus, putamen, and temporal poles. This included areas in the left posterior and anterior cingulate gyri and bilateral lobes VIIb, VIIIa, and Crus I in the cerebellum, as well as left VI and right Crus II lobes.
Density differences were also observed between the sexes. Males tended to have denser left amygdala, hippocampus, insula, pallidum, putamen, claustrum, and areas of the right VI lobule of the cerebellum, among others. Females, on the other hand, tended to have denser left frontal pole.
The significance of these differences lies in both the lateralization—males having more volume in the left hemisphere and females having more volume in the right hemisphere—and the potential utility of these findings in exploring distinctions in neurological and psychiatric conditions. Transgender Studies: Initially, investigations into the neurological distinctions of transgender individuals after death concentrated on the hypothalamic and amygdala regions of the brain. Through the application of magnetic resonance imaging (MRI), certain trans women were observed to possess putamina with dimensions akin to those typical of females, exceeding the sizes observed in cisgender males. Additionally, specific trans women exhibited a central region of the bed nucleus of the stria terminalis (BSTc) and the interstitial nucleus of the anterior hypothalamus number 3 (INAH-3) that resembled the female pattern, as determined by the number of neurons within each structure. Mental Health treatment should be personalised to a certain degree to cater to the differences between men's and women's brains. By doing so, we see better outcomes and more area-specific treatment results. For example, men may need coping skills related to the way they express aggression and stigma when faced with mental health issues, and women similarly would need to be more empowered and taught to handle their role better despite the patriarchal bias within society.