Concussions and, even lesser "subconcussive" head trauma [1], may speed up the brain's natural aging process says a recent study (1).
Researchers from the University of Michigan School of Kinesiology and the U-M Health System looked at college students with and without a history of concussion and found changes in gait, balance, and in the brain's electrical activity, specifically in the areas measuring attention and impulse control.
The declines were present in the brain injury group up to six years after injury, though the differences between the study groups were very subtle, and outwardly all of the participants looked and acted the same.
Lead author Steven Broglio, Assistant Professor of Kinesiology and Director of the Neurotrauma Research Laboratory at UM, stressed that, at this point, the study is only advancing a yet-to-be-proven theory that concussions and head impacts may accelerate the brain's natural aging process.
"The last thing we want is for people to panic. Just because you've had a concussion does not mean your brain will age more quickly or you'll get Alzheimer's," Broglio was quick to emphasize. "We are only proposing how being hit in the head may lead to these other conditions, but we don't know how it all goes together just yet."
Broglio stressed that the influence of various lifestyle and environmental factors, such as smoking, alcohol consumption, physical exercise, family history (genetics), whether or not a concussed athlete "exercises" their brain, and even how dense the gray matter in a person's brain is, which gives them greater "cognitive reserve" to draw upon may also impact the brain's aging process, and that "concussion may only be one small factor."
In addition, he said, this line of research is still in its infancy. "'It's not entirely clear," Broglio told the Kalamazoo News [2], "if and how the brains of young athletes are affected by the sports they play. 'We are realizing it's probably not how many concussions you have that makes a difference, but the total exposure' to concussive and sub-concussive blows."
To begin to understand how concussions might impact brain activity and its signaling pathways, researchers asked the participants to perform certain tasks in front of a computer, while their brain activity was measured via electroencephalogram (EEG. The brains of the nonconcussed group showed a greater area of electrical activation than the participants with a history of brain injury.
"What we don't know is if you had a single concussion in high school, does that mean you will get dementia at age 50?" Broglio said. "Clinically, we don't see that. What we think is it will be a dose response.
"So, if you played soccer and sustained some head impacts and maybe one concussion, then you may have a little risk. If you went on and played in college and took more head balls and sustained two more concussions, you're probably at a little bigger risk. Then if you play professionally for a few years, and take more hits to the head, you increase the risk even more. We believe it's a cumulative effect."
Does the average high school athlete face risks similar to those of former professional football players - such as those whose brains, upon examination after death, show signs of chronic traumatic encepholapathy (CTE) [3], or who, even if still alive, exhibit signs of serious depression or early-onset dementia which researchers have linked to their years on the playing field?
Broglio says that there is little to no evidence that they do. "We're not seeing an epidemic of men in their early 50s with early Alzheimer's because they played high school football," Broglio told a Michigan newspaper [2] in commenting on the study.
But the study, along with several others (most notably, by researchers at Purdue [1] (2)), appears to provide additional support for those calling for limits to be placed on the amount of repetitive brain trauma exposure to which athletes playing contact and collision sports at the youth and high school level are exposed.
The Purdue study, among others, shows that football players can experience as many as 1,000 impacts or more over the course of a single season, much of it in practices. The National Football League, the Ivy League, and, at the youth level, Pop Warner, have adopted rules limiting the number of full contact practices in an effort to reduce the number of subconcussive hits football players experience.
So far, however, such limits have not been adopted at the high school level, where four or five days per week of full contact practices are still the norm.
Sport-related concussions has been traditionally viewed as a transient injury without long-term consequences, although the studies on this relationship are mixed, and the tests used were not designed to detect subtle long-term decline in cognitive performance after injury. Over the past several years, Broglio and his colleagues have wondered whether, if more sensitive cognitive measures were utlized, differences in cognitive function between those with and without a history of concussion might be detected.
Utilizing a particular aspect of electroencaphograms (EEG) known as event-related brain potentials (ERPs), and focusing within the ERP assessment on the ability of test subjects to attend to and discriminate between stimuli in the split second after stimulation (called the P3 response), Broglio found in a 2009 study [4](3) significant reductions in the amplitude of the P3b wave (a subcomponent of the P3 signal, which occurs in the brain in reaction to an expected but infrequent event) for those with a concussion history compared to those without a history of concussion. They also found a significant reduction in the amplitude of the N2 component of ERP, which measures one's ability to monitor responses and inhibit inappropriate motor responses. Both of these subtle yet statistically significant deficits were found in the concussed group despite a lack of significant clinical differences in results between groups on the ImPACT neurocognitive test [5].
In a follow-up investigation (4), Broglio and his colleagues also found poorer response accuracy after an erroneous response among the previously concussed group, and that is as the number of concussions increased, the ability to self-correct declined.
In the most recent study (1), Broglio views the findings in the two 2009 studies as showing that "sport concussion can no longer be thought of as a transient injury resulting in a short-lived neurologic impairment" because "the young adults evaluated in these investigations showed a decreased ability to maintain attentional resources toward 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 electrophysiological changes do exist well beyond the acute injury stage." (1)
In addition, Broglio noted, the decreased ability to maintain attentional resources documented in young adults with a concussion history mimicked those seen in older adults transitioning from a stage of mild cognitive impairment to Alzheimer's disease.
Combining the knowledge that concussion is a diffuse brain injury and their work showing persistent electrophysiological changes in brain function, Broglio and his colleagues then set out to test a theory that concussion may also have a lasting effect on motor control, specifically balance and gait, comparing a group of 162 collegiate athletes with no previous injuries and 62 who reported between 1 and 4 concussions.
On the balance tests, the results indicated a shift in balance strategy by those with a concussion history demonstrating less control over medial/lateral (e.g. side to side) sway, similar to what has been reported in otherwise healthy older adults and has been correlated with an increased risk for falls.
"This raises the likelihood that individuals with a concussion history may be at greater risk for falls, especially as they age," the study suggests, and provided additional support for the findings in the 2009 studies of permanent changes in cerebral function after concussion as measured by ERP, with the changes not isolated to cognitive functioning but extending to motor functions such as postural control" (i.e. balance).
Having established that concussive injuries can have a lasting effect on motor control, Broglio and his colleagues then sought to evaluate how the injury may affect gait. They found that those with a concussion history "subconsciously elect to maintain a more safer and secure gait pattern," which they speculated may be a protective mechanism to reduce the risk of further injury from falling. Unlike the balance changes, Broglio said, "changes to gait after concussion have a much greater implication for influencing injury risk with age," especially, because of the strong link between age-related declines in cognitive functioning that are known to influence walking negatively, and because impaired gait has been shown to predict chronic disability, long-term nursing home care, and mortality.
Given the clear subclinical differences on cognitive and motor control tests between the concussed and control groups, Broglio speculated that, as the concussion group ages, the changes may manifest into clinically significant functional impairments.
While the cognitive reserve of previously concussed young adults likely compensates for the subtle deficits the three studies documented, "as these individuals age and the anticipated cognitive declines associated with aging ensue, these differences may become larger and more meaningful in some portion of the population," writes Broglio.
While some may be able to withstand a concussion without a clinicallly meaningful decline in function later in life, and intrinsic factors may play a role in the cognitive decline of otherwise healthy individuals, the concern is that "those with a concussion history may experience a faster rate of deterioration and face clinically meaningful declines at an earlier age and to a greater degree than their uninjured counterparts. Conversely, there likely is a subset of the population that may be able to sustain a concussion without clinically meaningful declines because of their reliance on cognitive reserve."
In the final analysis, writes Broglio, this line of research:
supports the hypothesis that concussion can no longer be thought of as a transient injury void of long-term consequences. Individuals sustaining a single concussive episode in the teen years show subtle negative alterations in brain function and motor control. The magnitude of those changes in later life remains in question. Anecdotal findings suggest that many athletes with a limited number of injuries have continued on to be high-functioning adults, whereas others are at risk for earlier and more severe declines in cognitive and motor performance. ... Despite the subtle changes in brain functioning, alternate cerebral pathways are recruited to achieve the same goal without clinical deficit. With time, aging, and the influence of various lifestyle and environmental factors, these alternate pathways may become less effective with clinical consequences in both cognitive and motor function.
In the next phase of study, researchers will look at people in their 20s, 40s and 60s who did and did not sustain concussions during high school sports. They hope to learn if there is an increasing effect of concussion as the study subjects age.
1. 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.
2. 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.
3. 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.
4. Pontifex MB, O'Connor PM, Broglio SP, Hillman CH. The association between mild traumatic brain injury history and cognitive control. Neuropsychologia 2009; 47:3210-6.
Some of the material in this article originally appeared in another form in a press release issued by the University of Michigan.
Posted October 10, 2012
Links:
[1] https://mail.momsteam.com/node/4492
[2] http://www.mlive.com/news/kalamazoo/index.ssf/2012/10/concussions_hit_home_what_the.html#incart_river_default
[3] https://mail.momsteam.com/node/3289
[4] https://mail.momsteam.com/node/2604
[5] https://mail.momsteam.com/node/801
[6] https://mail.momsteam.com/sub-concussive/sub-concussive-hits-growing-concern-in-youth-sports
[7] https://mail.momsteam.com/health-safety/seven-ways-to-reduce-risk-of-brain-trauma-in-contact-and-collision-sports
[8] https://mail.momsteam.com/repetitive-brain-trauma-and-chronic-traumatic-encephalopathy-CTE-cause-and-effect-relationship-scientifically-premature
[9] https://mail.momsteam.com/5-7/limiting-hits-head-in-youth-sports-aim-innovative-hit-count-program
[10] https://mail.momsteam.com/subconcussive/frequent-soccer-heading-linked-brain-damage-impaired-memory-study-finds
[11] https://mail.momsteam.com/health-safety/cte-what-risk-athletes-who-stop-playing-football-after-high-school