Toronto, CANADA - People who make a full recovery from head injury often report "mental fatigue" and feeling "not quite the same" - even though they scored well on standard cognitive tests.
Now brain imaging experts with Baycrest's Rotman Research Institute in Toronto have found a distinct "brain signature" in patients who have recovered from head injuries that shows their brains may have to work harder than the brains of healthy people to perform at the same level.
The patients in the study had diffuse axonal injury (DAI), the most common consequence of head injuries resulting from motor vehicle accidents, falls, combat-related blast injuries, and other situations where the brain is rattled violently inside the skull causing widespread disconnection of brain cells.
"Our imaging data revealed that the DAI patient brains had to work harder to perform at the same level as healthy, non-injured brains. Specifically, the brain injury patients showed a greater recruitment of regions of the prefrontal cortex and posterior cortices compared to healthy controls," said Dr. Gary Turner, who led the study as a part of his doctoral studies at Baycrest and the University of Toronto with senior author and Rotman scientist Dr. Brian Levine. The study is published in the Sept. 9th issue of Neurology, the medical journal of the American Academy of Neurology.
Even though the head injury patients performed as well as the healthy controls on a series of working memory tests that measured their ability to organize, plan and problem solve, the fact their brains had to work harder is an indication of "reduced cognitive efficiency", explained Dr. Turner, who is now completing a post-doctoral fellowship with the Helen Wills Neuroscience Institute at the University of California, Berkeley, where he is working to develop assessments and programs to enhance cognitive skills in people with head injury and normal aging patients.
Using standard techniques for imaging resting brain function, doctors typically look for reduced blood flow in certain regions to indicate neural damage. The Baycrest study used functional magnetic resonance imaging (fMRI) to assess brain activity during performance of a mentally challenging task involving the control and manipulation of information held in mind. This "executive" or high level cognitive operation is important to many daily tasks, such as problem solving and organization
"Our study adds to an emerging line of evidence that increased blood flow to areas not normally recruited during challenging mental tasks is related to reduced cognitive efficiency in patients with head injury," added Dr. Levine, who is internationally-recognized for his research on recovery and reorganization of brain function after traumatic brain injury.
The eight patients in the Baycrest study had been in motor vehicle accidents several years prior, sustaining significant brain injuries that left them comatose for various lengths of time; yet all patients made good recoveries as evidenced by a return to pre-injury employment or school. Their fMRI scans were compared to 12 healthy adults, matched to the patients for age and education.
The Baycrest study is the first to recruit patients and healthy controls that were evenly matched in cognitive performance from the outset. The study included only head injury patients with DAI and not other large brain lesions - thus yielding the strongest evidence to date that head injury patients' brains work harder than those of non-injured people despite equivalent performance on tests - and that this is caused by DAI and not by other accompanying brain damage that can occur with significant head injury.
Approximately 1.4 million Americans sustain head injuries each year, with associated costs estimated at $40 billion (according to the Centers for Disease Control and Prevention). The bulk of these costs are attributable to cognitive and behavioural changes, yet these changes are not well understood because DAI is widespread and difficult to pinpoint using standard brain imaging techniques. According to calculations in the Canadian Institute for Health Information's 2007 Report - The Burden of Neurological Diseases, Disorders and Injuries in Canada - over 200,000 Canadians sustain head injuries each year.
Drs. Turner and Levine say their findings are an important step in the future development of therapies that will help brain injury patients become more efficient in their cognitive processing. "Using neuroimaging methods to measure 'cognitive efficiency' in the brain, as indicated by altered functional recruitment of brain regions during a memory task, may one day become a standard metric of rehabilitation outcome," said Dr. Levine.
The study was funded by a grant from the NIH - National Institute of Child Health and Human Development. Baycrest, an academic health sciences centre affiliated with the University of Toronto, is internationally renowned for its care of aging adults and its excellence in aging brain research, clinical interventions, and promising cognitive rehabilitation strategies.
"Augmented neural activity during executive control processing following diffuse axonal injury" is published in the Sept. 9th issue of Neurology (Vol. 71, 812-818).