Damage to the frontal lobes can affect a person’s ability to ‘stay on the job’
Toronto, CANADA — A new study sheds light on why brain injury patients have difficulty performing tasks consistently — a necessary requirement for holding a job. The findings may influence how clinical assessments of brain injury are conducted in future, encouraging doctors to pay closer attention to ‘variability’ of performance as a marker for impairment.
The study is published in the November issue of the journal BRAIN. It was led by Dr. Donald Stuss, Director of The Rotman Research Institute at Baycrest Centre for Geriatric Care, with Dr. Michael Alexander, Associate Clinical Professor, Neurology, Harvard Medical School in Cambridge, Mass.
“Our study has shown that damaging certain areas of the frontal lobes can impair our ability to perform consistently — a key requisite for holding a job,” says Dr. Stuss. “Many people who suffer brain injuries from an accident, tumor, or stroke for example, may make considerable progress in their rehabilitation, but somehow have difficulty in daily life. The one area that may give them trouble — performing consistently on tasks, both within a task and at different times — may be the most difficult and nuanced for doctors to pick up on with a ‘single’ clinical assessment. The patient may need to be assessed more than once over a period of time. Inconsistency over repeated assessments is an important measure of impairment.”
The inspiration for this frontal lobe study came about 15 years ago when Dr. Stuss and his colleagues were testing brain injury patients in studies. They discovered that some patients would perform normally on the first test, but then one week later perform poorly on the same test. Because the data was not replicable over the short interval, it was assumed to be statistical “noise” — that is, scientifically unimportant. The results had to be rejected due to inability to replicate the findings. Fortunately, a parallel study in mild head injury patients who were tested not twice but five times over several weeks on the same test, revealed similar variability in performance.
“What we came to realize was that what we had been taught for years as the death knell of an experiment — the lack of replicable findings — in certain circumstances is the finding itself. The “noise” in the data was the data! It was the source of considerable information for us,” says Dr. Stuss. This realization became the basis for developing the study that is now published in BRAIN.
Since the earlier publications, numerous studies have confirmed reduced consistency in patients with traumatic brain injury at all levels of severity, with or without focal frontal lesions. Performance variability has also been reported in dementing illness, attention deficit disorder and schizophrenia. However, there has been no direct experiment to determine if lesions in ‘any’ focal region of the frontal lobes are critical for performance variability. Dr. Stuss wanted to investigate whether different frontal lobe lesions were particularly important in impairing sustained attention and task performance. The importance of this study is that it addresses the mechanisms underlying the observation, a necessary step in developing targeted rehabilitation.
Thirty-six patients who had suffered brain injuries as a result of trauma, stroke, hemorrhage or removal of a benign tumor, were part of the study. The patients were divided into five groups depending on the location of their primary lesion. Eleven patients had lesions located in nonfrontal regions. The other 25 patients had focal frontal lesions and were divided into four groups based on the location of their primary lesions — left dorsolateral frontal, right dorsolateral frontal, inferior medial, and superior medial. The five patient groups were compared to 12 normal, control subjects.
The subjects completed four different reaction time computer tasks that ranged from simple to increasingly more complex; the latter supposedly demanding more involvement from the executive functions located in the frontal regions of the brain. Each task required the subject to press a button with their dominant hand when they saw a particular target image that they were told to watch for. There were four primary image shapes — circle, square, triangle and cross. They were alerted to a particular target to watch for that had specific characteristics of shape, color and internal texture — for example a red circle with horizontal lines. Subjects were instructed to respond as quickly and as accurately as possible when they saw this target. If they saw a non-target image, they were to press the other button that was in their non-dominant hand. This testing session was repeated on two additional occasions, each a week apart. Researchers focused on two major measures: a) the variability while doing a task over time at one sitting; and b) “consistency of performance” — the ability of an individual to perform comparably across different testing sessions. Results were correlated to task complexity as well as location of brain lesion.
While there was minimal variability with nonfrontal lesions, all of the frontal patient groups (except the inferior medial) had some degree of inconsistency of performance. Those with frontal lesions in the dorsolateral (right and left) and superior medial areas, showed the most performance variability — even on the simplest tasks. “We found that individual variability is significantly increased in most patients with frontal injury, but the effects are not uniform across all frontal regions,” says Dr. Stuss. “Most importantly, we discovered that different frontal brain regions result in variability for different reasons.”
Investigators made four conclusions from the study: (1) Performance variability may be caused by damage to specific brain regions. Lesions in the frontal lobes, in particular, impair stability of behavior; (2) These fluctuations of performance in an individual are not simply statistical noise but an important measure of impairment; (3) Different types of variablity are affected by damage in different brain regions; (4) Task factors have important effects on demonstration of variability.
These results provide a means for investigating why some patients seem to recover fully, yet are not able to hold down a job. Understanding that different brain regions result in variability of performance for different reasons is the first step in treating these disorders. Dr. Stuss says future research should look more closely at the interaction of frontal lesion involvement, specific task demands and task complexity.
Funding for the study was provided by the Canadian Institutes of Health Research. Dr. Stuss’s team included Dr. Michael Alexander, Harvard Medical School; and statistician Malcolm Binns and post-doctoral student Kelly Murphy, both with The Rotman Research Institute at Baycrest.