Scientists are appealing for more people to donate their brains for research after they die.
They say they are lacking the brains of people with disorders such as depression and post-traumatic stress disorder.
In part, this shortage results from a lack of awareness that such conditions are due to changes in brain wiring.
The researchers' aim is to develop new treatments for mental and neurological disorders.
The human brain is as beautiful as it is complex. Its wiring changes and grows as we do. The organ is a physical embodiment of our behaviour and who we are.
In recent years, researchers have made links between the shape of the brain and mental and neurological disorders.
More than 3,000 brains are storied at the Harvard Brain Tissue Resource Center at McLean Hospital just outside Boston. It is one of the largest brain banks in the world.Image caption Harvard Brain Tissue Resource Center is one of the largest such banks in the world
Most of their specimens are from people with mental or neurological disorders.
Samples are requested by scientists to find new treatments for Parkinson's, Alzheimer's and a whole host of psychiatric disorders.
But there is a problem. Scientists at McLean Hospital and at brain banks across the world do not have enough specimens for the research community.
According Dr Kerry Ressler, who is the chief scientific officer at McLean hospital, new treatments for many mental and neurological diseases are within the grasp of the research community. However, he says it is the lack of brain tissue that is holding back their development.
"We have the tools and the ability to do some great deep-level biology of the human brain now.
"What we are lacking are the tissues from those with the disorders we need to really understand."
One donor visiting the hospital, who wished to be known only as Caroline, told BBC News that she decided to donate her brain for medical research partly because her sister has schizophrenia.
She hopes that her donation will help researchers find a cure – and she's urging others to do the same.
“My parents were fine but why did my sister get schizophrenia? We are not sure where it came from. How are we going to find out if we don’t do the research on the brain, which is where the problem is."Image caption Prof Sabina Berretta wants to challenge the misconceptions that surround her field
There is a shortage of brains from people with disorders that are incorrectly seen as psychological – rather than neurological in origin. These include depression and post-traumatic stress disorder.
Prof Sabina Berretta, the scientific director of the Harvard Brain Tissue Resource Centre, said: "If people think that there are no changes in the brain of somebody that suffers from major depression or post-traumatic stress disorder then there is no reason for them to donate their brain for research because (they think that) there is nothing there to find.
"This conception is radically wrong from a biological point of view."