Limit hits
But the study, along with several others (most notably, by researchers at Purdue (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.
Concussion not a transient injury
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(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.
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.
