Motherhood is good for the brain, causing neurological changes that make females braver, faster and less stressed, a US researcher says.

The finding, presented at this week's International Congress on Women's Mental Health in Melbourne may lead to chemical therapies that could help make 'good' mothers.

Craig Kinsley, Professor of Neuroscience at the University of Richmond's Department of Psychology, says all female mammals change some of their critical behaviours after giving birth.

These are normally behaviours that are linked to a mother's ability to care and protect her offspring.

In tests on rats young mothers showed better maze negotiation skills and memory, and decreased levels of stress and fear.

"Mothers become more protective of their offspring and will defend against a predator twice their size," he says.

"They overcome their fear and are very capable of defeating the predator."