A brain area presumed to be involved only in co-ordinating movement also controls higher functions, such as vision, mounting evidence suggests.
The cerebellum sits below the larger cerebrum
Traditionally, higher mental processing has been seen as the cerebrum's job - the evolutionary newest and largest part of the brain.
The cerebellum or "little brain", which sits below the cerebrum, was thought to control balance and movement.
A study of brain-injured infants shows this view is too simplistic.
The research in Pediatrics looked at 74 babies born prematurely who had varying degrees of brain damage.
The Harvard team from the Children's Hospital in Boston used magnetic resonance imaging (MRI) brain scans to look at the injuries in detail.
When there was injury to the cerebrum, the cerebellum also failed to grow to a normal size.
When the cerebral injury was confined to one side, it was the opposite half of the cerebellum that failed to grow normally.
Similarly, when injury occurred in one cerebellar hemisphere, the opposite side of the cerebrum was smaller than normal, which the researchers said suggested there was an important developmental link between the two parts of the brain.
Other work by Dr Catherine Limperopoulos and her colleagues suggests in addition to motor problems, children born with cerebellar injuries have problems with higher cognitive processes such as communication, social behaviour and visual perception.
Dr Limperopoulos said: "Until recently, cerebellar injury was under-recognised.
"Doctors downplayed it, saying, 'Oh, maybe Johnny will be a little clumsy'.
"Our research has made us aware that cerebellar injury is not a benign finding.
"We now know to look for it and can counsel families that their children are likely to have deficits that extend beyond motor, and that may benefit from early intervention."
Studies suggest that the cerebellum grows rapidly in babies while in the womb during the latter stages of pregnancy and therefore those who are born prematurely are at much greater risk of damage to this part of the brain.
As more premature babies are surviving, thanks to advances in medical treatment, more children are growing up with cerebellar damage, they said.
Professor Mitchell Glickstein, from University College London, said: "It's an interesting study."
He said the idea of the cerebellum involved in cognition was not new, but the study authors had looked at the anatomical detail with modern imaging.
He said there was controversy over how much involvement the cerebellum might have in functions other than movement, such as language and cognition.
In his view, he does not think it is directly involved in language, but is definitely involved in speech.
He said its role was more complex than simple motor co-ordination.
"Although the evidence for it being involved in cognition is modest, the evidence for anatomical linkage with the cerebral cortex is powerful.
"It may be that the cerebellum and its connections can help in patients with severe motor disability caused by diseases of the basal ganglia."
For example, some patients with Parkinson's disease are still able to carry out some actions swiftly and surely, such as catching a ball, even though their general motor control is poor.
"It may be that if the sensory mechanism is appropriate for the cerebellum, they can do these remarkably skilled things like catching a ball."