How brain folds differ between males and females – and why twins help us understand it

The brain’s surface is covered in folds called sulci, which vary from person to person. Our study focused on three folds in the temporal lobe: the rhinal sulcus (RS), collateral sulcus (CS), and occipito-temporal sulcus (OTS).

Working with international collaborators, we asked:

1. How often do these folds connect?
2. Do these connections differ between males and females?
3. How much is due to genetics?

Using twins from the Queensland Twin Imaging (QTIM) study, we found:

• Clear sex differences, especially in the right hemisphere.
• Genetics explain 28–45 per cent of variation in these brain connections.
• Some genes influence multiple sulcal connections

Brain structure isn’t one-size-fits-all—it varies by sex and is partly inherited. Twins were key to separating genetic from environmental effects, confirming that some brain folds run in families. This insight could improve understanding of brain health and disease for everyone.