Sex Differences in Human Brain Structure at Birth

Context: A recent study published in the Biology of Sex Differences journal has examined the brain differences between newborn male and female infants.

Different Brain Size and Composition

• Boys:
  • Larger brain volumes: On average, male infants had significantly larger intracranial and total brain volumes, even after controlling for birth weight.
  • More white matter: Boys had more white matter.
• Girls:
  • More grey matter: Female infants showed larger volumes of grey matter in areas linked to learning, speech and cognition, such as memory and emotional regulation.
  • Regional differences: Grey matter was particularly larger in regions related to memory and emotion regulation.

Significance of White and Grey Matter

• White matter consists of long nerve fibers that facilitate communication within the brain.
• Grey matter is critical for cognition, memory and learning.

Functional Implications

• Boys’ Brains: Larger volumes of white matter in areas involved in sensory processing and motor control, reflecting more developed capabilities in these areas at birth.
• Girls’ Brains: Larger grey matter volumes in regions crucial for learning, speech, and cognitive processes, suggest a possible advantage in early development related to memory and emotions.

This study has proved that Sex-specific brain differences are already present in the earliest days of life, i.e. these are inherent to brain development before external environmental factors come into play.

Brain Structure and Function

Male and female brains have been found to differ in terms of both structure and function. Some studies suggest that males generally have a larger brain volume, but females tend to have a higher proportion of grey matter.

• Certain areas of the brain, such as the hippocampus (related to memory) and the amygdala (related to emotions), may show sex differences in size and activity.
• Males and females also tend to exhibit different cognitive and emotional processing, which may be linked to hormonal influences during development.

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