Factors that appear to impair

cognitive performance are a history of previous concussion, number and duration of postconcussion symptoms, and being a younger-aged high school athlete compared with a collegiate or professional athlete. Five studies9, 15, 21, 22, 23 and 24 assessed the effect of concussion history on cognitive function. Two phase II9 and 15 and 1 phase I21 study indicated worse cognitive function for those with a history of previous concussion 5-FU manufacturer compared with those without, while 2 phase I studies22, 23 and 24 found no group differences. In the first group of studies, statistically significant impairments in verbal memory and reaction time were found in college athletes approximately 1 week after a new concussion. In another study,21 college athletes with a previous history of concussion reported more cognitive symptoms than

those without (P<.05), with 32% endorsing 1 or more cognitive symptoms at the 1-week assessment versus 8% in those without a previous history of concussion. Additionally, professional Australian footballers with a history of concussion performed significantly worse than those without on visual motor speed (d=−.55; 95% confidence interval [CI], −1.02 to −.08), impulse control (d=−.88; 95% CI, −.40 to −1.36), and processing speed tests (d=−.41; 95% CI, −.88 to .05). 9 In the other group of studies, an association between concussion history and cognitive performance was not found in college or professional American football/National Football League players as assessed by traditional Bortezomib mouse 22 and 23 and computerized tests. 24 The amount of time between concussions is a potentially important confounding variable but was only reported in 1 of the studies9 that suggested worse cognitive function in those with a history of previous concussion. In

those MTMR9 with 3 or more concussions, the mean ± SD number of days since the previous concussion was reported to be 561±672.9 The amount of time between successive concussions may affect the outcome and account for some of the different findings. For instance, 2 concussions within a 6-month period may lower cognitive performance more than, say, 2 concussions within 12 months. Commonly reported postconcussion symptoms include headaches, balance problems, dizziness, fatigue, depression, anxiety, irritability, and memory and attention difficulties.27 Six studies15, 16, 17, 20, 23, 25 and 26 examined the relationship between postconcussion symptoms and objective evidence of cognitive impairment, as assessed with neuropsychological tests within 2 weeks postinjury. Postconcussion symptoms were mainly self-reported and included cognitive symptoms (eg, memory problems) and physical symptoms (eg, headache).