The state's Public Advocate, Colleen Pearce, said the $400,000 gift - provided on an anonymous basis - was the largest donation her office had ever received.

Ms Pearce said prisoners were about 20 times more likely (42 per cent of men and 33 per cent of women) to have an acquired brain injury than people in the general community (2 per cent). Yet many prisoners went undiagnosed and lacked specialist support, she said.

''They are doing criminal acts, that's why they're there. But what we need to do is understand why they're so overrepresented and what we can do to prevent them from entering the criminal justice system.''

Ms Pearce said the money will fund three research projects over the next three years, which she hoped would lead to ideas for policy and law reform ''to improve the way we treat people with an acquired brain injury within the criminal justice system''. Such injuries can be a result of stroke, a blow to the head or alcohol and drug abuse.

The donation will fund:

■ RMIT's Centre for Innovative Justice and the Jesuit Social Services to gather a focus group of people with acquired brain injuries who have previously been arrested or gone to prison, to help educate others on their experiences.

■ Monash University to interview people with acquired brain injuries and criminal justice professionals, including lawyers, police and prison officers, to identify potential law reform in the area.

■ Brain-injury specialist organisation Diverge to deliver training workshops on people with acquired brain injuries to workers in the disability and justice sectors.

Some of the symptoms of acquired brain injury could explain why many people with it were in prison, Ms Pearce said. They included a difficulty regulating emotional responses and inhibitions, and a lower capacity to learn from mistakes. ''They're impulsive but also likely to repeat behaviours,'' she said. ''Damage to the frontal and temporal lobes of the brain is also associated with an increase in the potential for aggressive, violent and criminal behaviour.''

Ms Pearce said many people living with an acquired brain injury in the community often also lacked support needed for daily tasks, such as how to use public transport or manage their money. ''They're some of the most vulnerable and disadvantaged in our community.''

She said it would be important to make sure such people had access to its services when DisabilityCare Australia was fully rolled out around the country: ''If you're not diagnosed, then you haven't even got past first base.''

jane.lee@fairfaxmedia.com.au