Perceptual Asymmetries

From cognition and perception to language in the brain

Sexing the Brain, Part 4: Function and Neuroimaging

What do we know about sex differences in the brain?

This post wrestles with this question: Are males and females using different parts of the brain when tackling a given task?

I chose the word “wrestle” because, when exploring relevant literature that addresses this question, the issues of specific task and brain localization become difficult to tease apart. For starters, in keeping with a conclusion implied in my previous post [Sexing the brain 3 (lateralization and neuroimaging)], I will focus on areas where behavioral sex differences have been reported. Furthermore, I will focus on meta-analyses rather than summarizing what has been published. Therefore, this leaves us mostly with spatial abilities, especially mental rotation (Voyer, Voyer, & Bryden, 1995), emotion recognition (Thompson & Voyer, 2014), and object location memory (Voyer , Postma, Brake, & Imperato-McGinley, 2007) as relevant areas of where to look for meta-analyses of imaging studies examining specific regions of interest. Math and verbal abilities, long believed to be male and female domains, respectively, are now known to produce only trivial sex differences (Hyde & Linn, 1988; Lindberg et al., 2011), so that excludes these areas as potentially meaningful in the search for sex differences in functional brain activation. Essentially: What is the point of looking for differences in the brain if they do not result in observable differences in behavior?

So, let us start with emotion recognition. Here, the meta-analysis by Stevens and Hamann (2012) showed sex differences in activation as a function of emotional valence (negative, positive). For negative emotions, they found greater activation in women than men in the left amygdala, left thalamus, hypothalamus, mammillary bodies, left caudate, and medial prefrontal cortex. For positive emotions, men typically have greater activation than women in the left amygdala, bilateral inferior frontal gyrus, and right fusiform gyrus. Essentially, aside from the left amygdala, there is little correspondence between the areas involved so there are actually sex differences in localization but it depends on emotional valence. In contrast, Wager, Phan, Liberzon, and Taylor (2003) had found no influence of valence but their analysis of this aspect did not include sex of participants as another moderating factor.

For spatial abilities and object location memory, it seems that a meta-analysis examining sex differences in activation observed in functional neuroimaging has yet to be done. Nevertheless, for mental rotation, a summary of some findings is presented in Voyer et al. (2006), testifying to the variability of results. One could argue that the absence of a meta-analysis for spatial abilities could be a reflection of the scarcity of relevant research. However, considering that Zacks (2008) included 32 articles in a meta-analysis focusing on the brain regions involved in mental rotation alone, scarcity of relevant research is unlikely. Unfortunately, Zacks did not consider gender differences in his analysis.

Although an analysis specific to object location memory also has yet to be done, lack of relevant research cannot account for this either, at least from the perspective of the review conducted by Postma, Kessels, and van Asselen (2008). Nevertheless, a meta-analysis by Hill, Laird, and Robinson (2014) examined sex differences in activation during working memory tasks. They found that, in females, such tasks activate more limbic areas such as the amygdala and hippocampus as well as prefrontal structures such as the right inferior frontal gyrus. In contrast, males tend to show more distributed activation that includes parietal regions. Whether such findings would extend to object location memory in the literature as a whole remains an empirical question.

Having considered the meta-analyses available so far, an important point arising from the above is that it is crucial to consider details of the tasks to draw conclusions on sex differences in activation. For example, in emotion recognition, neglecting emotional valence could produce invalid results in that particular case. In fact, for any cognitive ability, the specific task used or how it was implemented could have dramatic effects on activation patterns. From this perspective, I would argue that researchers need to standardize tasks and methods when investigating sex differences. Essentially, we need to validate our behavioral tasks before neuroimaging testing to ensure that they show the expected effects under “normal” circumstances (i.e., outside of the scanner).

In reality, the meta-analyses required to draw solid conclusions concerning functional sex differences in the brain in this post have yet to be done. Therefore, it might be a good idea for me to revisit this blog post in a few years.

In the meantime, as a conclusion to this series of posts, I would say that, aside from an overall size difference, there are no sex differences in anatomy and structure. Some differences in lateralization and localization of emotions might exist. Other areas are still waiting for quantitative summaries. In short, sex differences are not in the shape of the brain, but how we use it!

 

References

Hill, A. C., Laird, A. R., & Robinson, J. L. (2014). Gender differences in working memory networks: A BrainMap meta-analysis. Biological Psychology. Advance online publication. doi: 10.1016/j.biopsycho.2014.06.008

Hyde, J. S., & Linn, M. C. (1988). Gender differences in verbal ability: A meta-analysis. Psychological Bulletin, 104, 53–69.

Lindberg, S. M., Hyde, J. S., Petersen, J. L., & Linn, M. C. (2011). New trends in gender and mathematics performance: A meta-analysis. Psychological Bulletin, 136, 1123–1135.

Postma, A., Kessels, R. P.C., & van Asselen, M. (2008). How the brain remembers and forgets where things are: The neurocognition of object–location memory. Neuroscience & Biobehavioral Reviews, 32, 1339-1345.

Stevens, J. S., & Hamann, S. (2012). Sex differences in brain activation to emotional stimuli: A meta-analysis of neuroimaging studies. Neuropsychologia, 50, 1578– 1593

Thompson, A. E., & Voyer, D. (2014). Sex differences in the ability to recognise nonverbal displays of emotion: A meta-analysis. Cognition & Emotion. Advance online publication. doi:10.1080/02699931.2013.875889

Voyer, D., Postma, A., Brake, B., & Imperato-McGinley, J. (2007). Gender differences in object location memory: A meta-analysis. Psychonomic Bulletin and Review, 14, 23-38.

Voyer, D., Butler, T., Cordero, J., Brake, B., Silbersweig, D., Stern, E., & Imperato-McGinley, J. (2006). The Relation between Computerized and Paper-and-Pencil Mental Rotation Tasks: A Validation Study. Journal of Clinical and Experimental Neuropsychology, 28, 928-939.

Voyer, D., Voyer, S., & Bryden, M.P. (1995). Magnitude of sex differences in spatial abilities: A meta-analysis and consideration of critical variables. Psychological Bulletin, 117, 250-270.

Wager, T.D., Phan, K.L., Liberzon, I., & Taylor, S.F. (2003). Valence, gender, and lateralization of functional brain anatomy in emotion: A meta-analysis of findings from neuroimaging. Neuroimage, 19, 513–531.

Zacks, J. M. (2008). Neuroimaging studies of mental rotation: A meta-analysis and review. Journal of Cognitive Neuroscience, 20, 1–19.

Daniel Voyer, Ph.D., is a professor at the University of New Brunswick in Canada.

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