An estimated 3.8 million sports-related traumatic brain injuries (TBIs) occur in the United States every year (Langlois et al., 2006), many of which are concussions (Gessel et al., 2007). Repeated concussions have been linked to early-onset Alzheimer's disease (Guskiewicz et al., 2005), depression (McCrory et al., 2009), dementia (Guskiewicz et al., 2005), and chronic traumatic encephalopathy (McKee et al., 2009).
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The models relating the left and right middle frontal gyrus (MFG; Table 3 and Table 4) are of particular interest because neuropsychological tests have indicated that changes in MFG activation are related to measureable decreases in verbal and visual working memory that have been documented in concussed indivdiuals (Hoskison et al., 2009).
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During this time, individuals may be in a vulnerable state, so that the blow that results in symptoms is the “straw that broke the camel's back.” If this concern is valid, a particular blow may cause a “physiological bifurcation” that places the brain in a distinct pathophysiological regime, much in the way that minor injuries precondition an eventual catastrophic tear in musculoskeletal soft tissues. Certainly, if concussion were a purely acute injury, the very strong connection we observed between blow history and neurophysiological changes should not exist.
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