Neuroscience and Gender Politics

Last year, students taking the subject ‘Sex and Gender in the Sciences’ took direct part in the public debates over neuroscience and gender politics. Led by Professor Cordelia Fine (HPS), the students held a focused class discussion on sensationalised research findings comparing female and male brains. Later, the students co-authored a statement on this issue, which was published by the Proceedings of the National Academy of Sciences (PNAS). HPS student Christine Polowyj reflects on this experience below.

In September 2024, the University of Washington published a media release promoting research conducted by Neva Corrigan, Ariel Rokem and Patricia Kuhl, which claimed that female brains are more vulnerable than male brains. The context surrounding this conclusion was the COVID-19 pandemic lockdowns which disconnected teens from direct contact with their peers.

“New research from the University of Washington, published online Sept. 9 in the Proceedings of the National Academy of Sciences, found the pandemic also resulted in unusually accelerated brain maturation in adolescents. This maturation was more pronounced in girls. When measured in terms of the number of years of accelerated brain development, the mean acceleration was 4.2 years in females and 1.4 years in males.”

Corrigan et al. interpreted these findings as indicating “the greater vulnerability of the female brain, as compared to the male brain”, to the social isolation of pandemic lockdowns, referencing research reporting teen girls as having higher levels of anxiety, depression and stress during the pandemic.

When this research was published, I was studying the History & Philosophy of science subject Sex and Gender in the Sciences (HPSC20023), coordinated by Professor Cordelia Fine. The paper was discussed in the context of feminism and values in science – serendipitously, our weekly topic. Our tutorial discussion led to our class co-authoring a letter replying to Corrigan et al., titled Uncertainty of Adolescent Brain Maturation Sex Difference Claims.

Our critique, together with a letter from neuroscientist Gina Rippon, was published by Proceedings of the National Academy of Sciences (PNAS). More recently, the journal published a letter focused on statistical issues, co-authored by Andrew Brown and colleagues. Corrigan et al. have directly responded to these letters, defending the validity of their neurobiological claims and the proposed role in poorer mental health outcomes for females.

While these exchanges are about science – hypotheses, measurement, statistics, inferences and conclusions – they take place within a bigger political picture. The vicious circle of gender bias is perpetuated when implicit gender norms and stereotypes are baked into scientific hypotheses and amplified through the media. Females – child, adolescent, adult or postmenopausal – are vulnerable to being labelled ‘weak’ or ‘crazy’. The mental stability of females has long been misunderstood and trivialised or declared pathological. Despite good intentions, neuroscience risks doing the same.

The gist of the exchanges in which our class participated is disagreement regarding whether the evidence offered by the researchers supports their assumptions and conclusions about the sex difference itself, why it might have arisen, and what it might mean.  

Disputes over the Sex Difference Claim

The emergence of COVID-19 and the resulting pandemic lockdowns presented an opportunity for the authors to use data collected from their original longitudinal study, mapping changes in adolescent brain structure under typical social conditions, to test a new hypothesis. Were there sex differences in the effects of the pandemic on adolescent brain development?

But how to compare the sexes? Corrigan et al. used a method of statistical analysis which has been dismissed as lacking rigour. As Brown et al. explain:

“Instead of comparing the sexes statistically to support their claims, Corrigan et al. tested for effects within each sex separately, declaring a sex difference when the null hypothesis was rejected in one sex but not the other. This approach has, for decades, been widely recognized as invalid. When applied to sex differences, it has been called the “Difference in Sex-Specific Significance” (DISS) error.”

This flawed statistical approach to testing for sex differences, they continue, “can result in false positive findings of difference up to 50% of the time – no better than flipping a coin.” After re-analysing the researchers’ open-sourced data and code, Brown et al. concluded that sex differences in cortical thinning was far less dramatic than Corrigan et al. had reported: only one brain region showed greater female to male cortical thinning relative to pre-pandemic counterparts – compared to the 30 regions identified by Corrigan et al.

In their reply, Corrigan and colleagues contest Brown et al.’s conclusion, reasserting the statistical significance of the sex difference (and acknowledging the contribution of an error on their part in the shared code provided to enable other researchers to run their own analyses on the dataset).

The exchange serves as a good reminder that scientists don’t unearth ‘pure’ facts about nature. Instead, scientific claims are the product of many, often highly technical and sometimes contested, decisions.

As such, scientists recruit values when deciding whether to make a particular claim, or how confidently to make it. Pointing to the inappropriate statistical comparisons in the original research, Gina Rippon criticised the researchers’ description of their findings as “notable” and “stunning” to the media. Other experts pointed out that the small sample sizes involved – ten or fewer participants in each sex-by-age group – was insufficient to make generalised claims.

Isolation, or (Gendered) Exposure?

As noted, the study originally intended to map changes in adolescent brain structure under typical social conditions. However, the pandemic lockdowns presented an historic opportunity to test a new hypothesis about sex differences under atypical social conditions.

But how to conceptualize those conditions? The researchers characterized the effect of lockdowns on adolescent brain development in terms of social isolation. However, adolescents might, in fact, have been in close social contact with others in the household, day in and day out. Lockdowns may also have increased social exposure between family members, potentially exacerbating existing tensions and dysfunctional dynamics in parent-parent, parent-child and sibling-sibling relationships.

These conditions might well have been gendered. Simply comparing the sexes on a neurobiological measure, without much considering what tends to ‘go with’ being a boy or girl in any particular time and place, risks mistaking social inequality for sex difference. Not accounting for other psychological stressors arising from gender norms, roles and stereotypes meant there was little chance to produce data that could challenge biological sex as the explanation for the observed neurobiological differences, or identify variables that have more explanatory power.

In our letter, we indicated it is likely that gendered expectations such as cleaning and caretaking would have burdened adolescent females, and that lockdown exposure increased the risk of harms from verbal, psychological and physical violence. These exposure stressors may have been more harmful than the stress experienced from peer isolation.

No Measurement of Purported Mechanism

The researchers state ‘typical adolescence’ is a time during which ‘many neuropsychiatric disorders’ emerge – namely anxiety, depression and behavioural disorders, and they emphasise emotional support as characteristic of female friendships.

Consequently, Corrigan et al. claim to have found evidence that the ‘lifestyle disruptions’ of the lockdowns had a ‘more severe impact’ on female brain biology. Supposedly, the ‘dramatic decrease’ in peer-to-peer connection during the lockdowns was reflected in female adolescent brains being more affected than male adolescent brains in the brain regions linked to social cognition.

However, our letter notes that the authors “offer no measure of the proposed mechanism of reduced social interaction (despite lockdown experiences being diverse)”. Nor did they take measures of the purported outcome to which females were apparently more vulnerable, such as depression, or show correlations of either with accelerated brain thinning.

Reverse Inference

The claim that social isolation from peers increases the risk of neuropsychiatric pathology in adolescent females also deserves some scrutiny. Questions arise: are the researchers unfairly pathologising the female experience?

It is often tempting for sex difference researchers to infer functional implications from structural differences. Known as ‘reverse inference,’ it can occur even when no actual behavioural differences have been identified. There is a long history of reverse inferences, infused with gender stereotypes, shoring up biological explanations of gender inequality.

Inferring greater psychiatric vulnerability in adolescent females from sex differences in the brain is a form of reverse inference. Indeed, pre-empting anxiety about the implications of accelerated cortical thinning, one of the researchers, Ariel Rokem, softened the claims in an interview to reassure parents. Besides stating the sex difference finding is speculative, he acknowledged thinning is typical in development, and acceleration may even be a protective mechanism.

In their reply, Corrigan et al. acknowledge this concern, stating that “[t]his is perhaps a situation in which careful research and judicious discussion can be helpful for science and society”. But we can ask to what extent the original research achieved this.

Nonetheless, it’s important to note the good intentions at play. Corrigan et al. argue for the importance of ‘ongoing monitoring’ of individuals whose adolescence coincided with the pandemic lockdowns, in order to support those who may be at risk of developing neuropsychiatric and behavioural disorders.

Conclusion

Critical engagement with sex difference in neuroscience research is crucial. Potentially over-generalised claims of accelerated brain maturation in females, inferred as indicating increased risk of developing mental disorders, reinforces the misconstrual of female as ‘the vulnerable sex’. Pushing back on research claims that are better described as speculative, rather than ‘notable’ or ‘stunning’, is both a feminist and scientific responsibility.

Hence, our letter. Being part of a critical engagement in the prestige publication PNAS alongside Gina Rippon and Donna Maney – whose work we studied – was a powerful experience that transformed tutorial discussion into critical engagement on the world stage.

Christine Polowyj is an HPS major interested in examining the epistemology of mental disorders. Christine is aiming to study honours in HPS to investigate how knowledge and belief formation intersects with causal theories of mental disorders, particularly Bipolar Affective Disorder.

Feature image: Self Preservation by Christine Polowyj