Changes in balance and gait
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.
Implications
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
