Study of 15,847 people worldwide uncovers sex differences in the asymmetry of major brain structures

There are age and sex related differences in the asymmetry of major brain structures, according to a study recently published in Brain Imaging and Behavior.

Human functions such as language, cognition and movement are produced by areas of the brain that are split asymmetrically between the two hemispheres. This means that the neural mechanisms behind certain brain functions often reside primarily in one half of the brain. This phenomenon is referred to as lateralization.

Lateralization varies hugely across humans in general, as the structure of an individual brain is quite unique. Differences in lateralization are also pronounced between men and women. For example, MRI studies have revealed that men show larger asymmetry in language centres of the cerebral cortex than women. Abnormal lateralization of the cerebral cortex has been linked to language impairments and psychiatric disorders.

Although lateralization of the cerebral cortex is well studied, the lateralization of structures found deeper in the brain known as, subcortical structures is not as well understood.

A team of scientists led by Tulio Guadalupe (Max Planck Institute for Psycholinguistics, The Netherlands) conducted research into the effects of sex, handedness and age on differences in asymmetry of subcortical brain structures. The team collected data from a large sample of 15,847 people taken from 52 existing MRI datasets.

The results showed sex differences in the asymmetry of the globus pallidus and putamen. The putamen was also found to be susceptible to asymmetry with age. Handedness was found to be unrelated to subcortical asymmetry.

Among the brain structures analysed, asymmetry in the globus pallidus, putamen, hippocampus and thalamus were the most strongly inherited. Meaning that these subcortical brain regions are the most likely to influence cognition and vulnerability to brain disorders though genetic variation. These findings are in agreement with multiple twin-based studies which have also found that genetics play a part in varying the asymmetry of subcortical structures like the amygdala.

Overall, it was found that although some subcortical structures are asymmetrical as a result of sex and age, others are influenced by our genetic makeup.

“We found reliable sex differences in asymmetries of the globus pallidus and putamen which, together with the hippocampus and thalamus, were also the most strongly heritable asymmetries among the seven structures analyzed,” the researchers concluded.

The study provides a more detailed understanding of lateralization in subcortical brain structures. However, this study clearly highlights the need for further research into the more subtle subcortical asymmetry and the impact it has on human behaviour.