That a sports concussions have an adverse short-term effect on cognitive functioning has long been known. But a number of recent studies support a growing body of evidence that the effects of concussions may linger for many months, even years.
Subtle and persistent deficits
A 2009 study1 by researchers at the University of Illinois found that a group of club and intercollegiate athletes averaging 3 ½ years post-injury and who performed normally on standard tests a sports-medicine practitioner would use to diagnose and evaluate concussion, had subtle and persistent decreases in the area of their brains used to process information about things going on in their environment which could only be detected using sensitive electromagnetic instruments.
"The issue becomes as they age, as natural aging takes over and cognitive processes slow down and decline, whether [the concussion] has an exacerbating effect," says Steven Broglio, Ph.D, A.T.C. co-author of the study and now an assistant professor of kinesiology in the Department of Kinesiology at the University of Michigan and director of the Neurotrauma Research Laboratory . "With age, you are less likely to pay attention to things going on around you that make you more susceptible to injury."
In a follow-up investigation,2 Broglio and his colleagues evaluated how 30 young adults with a history of concussion about 4 years prior and 36 control subjects with no history of concussion performed on an ImPACT neurocognitive assessment and how well they were able to suppress inappropriate responses after making an error (i.e. making more errors after making an error) while their brain activity was recorded (e.g. EEG). They found that, while there were no differences between groups on any of the ImPACT measures of cognitive function, the previously concussed group not only showed poorer response accuracy on the tests and poorer response accuracy after an erroneous response, but a suppressed response in the area of the brain used to correct those errors, with the response decreasing as the number of concussions increased.
These findings, Broglio suggests in a 2012 article,3 support the view that "sport concussion can no longer be thought of as a transient injury resulting from short-lived neurological impairment. "The young adults evaluated in these investigations showed a decreased ability to maintain attentional resources towards infrequent, yet expected events; less ability to inhibit incorrect responses to their environment; and a lessened ability to recognize that they had made a mistake. This represents clear evidence that persistent electrophysical changes do exist well beyond the acute injury stage," he writes.
Long-term deficits in working memory greater in teens
More recently, a Canadian study,4 found that concussed athletes of all ages - not just adults, but children and adolescents - continue to have subtle but persistent deficits in the area of their brains associated with working memory more than six months after injury,
Surprisingly, the study found that concussed teenage athletes not only performed significantly worse than younger children and adults on neuropsychological tests of short-term memory, but that activity in an area of their brains associated with working memory was significantly more impaired.
The authors, including Dave Ellemberg, PhD, a professor in the university's Department of Kinesiology, speculated that the greater vulnerability of teenagers to the effects of sport concussion may be related to the fact that the frontal part of the brain responsible for working memory and other executive functions is in its final stages of maturation during adolescence, so "that a blow to the head during this critical period of development could result in more severe deficits for adolescents compared to the other age groups."
Like the Illinois researchers, the Canadian researchers admitted that the implications of such deficits for a concussed athletes everyday life are not yet known.
More conservative approach to return to play suggested
While Broglio said it was "not clear if or how" the subtle cognitive deficits found in athletes with a history of concussion would "impact their day-to-day life," his first 2009 study concluded that a conservative approach to mTBI was clearly warranted.
"At the very least, those suspected of sustaining a concussion should be withheld from activity until they perform at or above a pre-[concussion] level of [cognitive functioning]" on standard neuropsychological tests.
Indeed, in light of the study's findings and those from other studies, Broglio suggested that a return to sports within one week following a concussion might be "extended out" to a month, as recommended by one college team doctor in a 2008 article in the Archives of Neurology, or at least by three weeks, as recommended by MomsTEAM's expert sports neuropsychologist, Rosemarie Scolaro Moser, Ph.D., in her 2012 book, Ahead of the Game: The Parents' Guide to Youth Sports Concussions.5
Cause for concern?
The deficits in working memory found in these studies may be present even in athletes with no concussion diagnosis.
A groundbreaking 2010 study by researchers at Purdue University6 found that high school football players who sustained a large number of hits in the 40 to 80 g range (i.e. subconcussive hits) also experienced impairment of visual working memory on neuropsychological tests, as well as altered activation in neurophysiologic function using sophisticated brain imaging tests (fMRI), although such impairment was not seen on re-testing before the next football season.
More concerning, "these players not only may be representative of the group associated with ‘unreported' concussions, but also are also likely to meet the criterion" for inclusion in a group which, because they suffer repetitive, sub-concussive blows to the head, may be at increased risk of further, long-term brain injury, such as CTE, said the study.
Taken together, the studies appear to provide additional support for those calling for youth and high school sports to reduce exposure of athletes, not just to the kind of hard hits that lead to concussion, but to repetitive subconcussive blows, both of which the studies show lead to cognitive deficits in working memory.
It remains to be seen if, as Randall Benson, a Wayne State University neurologist told Sports Illustrated, the Purdue, Illinois, and Montreal studies provide a "real-time snapshot" of the early stages of the corrosive creep that wears away at the frontal lobe" and, ultimately, to long-term brain injury, such as CTE.
1. Broglio SP, Pontifex MB, O'Connor P, Hillman CH. The persistent effects of concussion on neuroelectric indices of attention. J. Neurotrauma 2009;26:1463-1470.
2. Pontifex MB, O'Connor PM, Broglio SP, Hillman CH. The association between mild traumatic brain injury history and cognitive control. Neuropsycholgia 2009;47:3210-6.
3. Broglio SP, Eckner JT, Paulson HL, Kutcher JS. Cognitive Decline and Aging: The Role of Concussive and Subconcussive Impacts. Exer. and Sports Sciences Review. 2012;40(3):138-144.
4. Baillargeon A, Lassonde M, Leclerc S, Ellemberg D. Neuropsychological and neurophysiological assessment of sport concussion in children, adolescents and adults. Brain Injury 2012;26(3):211-220.
5. Moser RS, Ahead of the Game: The Parents' Guide to Youth Sports Concussions (Dartmouth College Press 2012).
6. Talavage T, Nauman E, Breedlove E, et. al. Functionally-Detected Cognitive Impairment in High School Football Players Without Clinically-Diagnosed Concussion. J Neurotrauma. 2010; DOI: 10.1089/neu.2010.1512.
Updated and substantially revised October 11, 2012
