Concussed adolescents have difficulty recovering the ability for high level thinking after injury and may require extended recuperation before full recovery of so-called 'executive function' is achieved, a new study finds. 
Researchers at the University of Oregon and University of British Columbia found that executive function was disrupted in concussed adolescents for up to 2 months after injury when compared to healthy control subjects.
The concussed teens had difficulties ignoring irrelevant but conflicting information when taking the Attentional Network Test (ANT), a widely used and well-studied test probing attention by assessing the relative change in reaction time to different stimuli, and that the impairment continued for up to 2 months post-injury, well beyond the time they reported being symptom-free on a concussion inventory, which typically occurred between 2 weeks and 1 month after injury, about twice as long as the impairment found in young adults.
The concussed teens also performed significantly worse than their uninjured peers on a Task-Switching Test (TST), which, as its name suggests, tests the ability to flexibly switch between competing task or stimulus-response rules, which previous studies had found to be highly sensitive to mild traumatic brain injury (mTBI) in adults but had not been studied in the concussed adolescent population.
"The results of this study suggest," said lead author David Howell of the Department of Human Physiology at the University of Oregon, "that tests which isolate components of executive function (ANT and TST) are sensitive to the effects of concussion in adolescents and reveal deficiencies that may last for at least 2 months after concussion. These data suggest that executive function testing may be a highly useful assessment to identify disturbances and track recovery following concussion for the adolescent population."
"This was a well-conducted study which adds further support to using neuropsychological testing as a supplement to the management of sport-related concussion," said William P. Meehan, III, a MomsTEAM concussion expert, and Director of both the Sports Concussion Clinic and the Micheli Center for Sports Injury Prevention in the Division of Sports Medicine at Boston Children's Hospital.
The study also suggests, said Dave Ellemberg, Ph.D., a Professor in the Department of Kinesiology at the University of Montreal, that expensive baseline neuropsychological testing is not required to determine cognitive impairment from concussion, and that comparing an athlete's post-concussion neuropsychological test results to those of athletes of the same age and gender (e.g. 'normative values') may be enough as a diagnostic tool. Ellemberg viewed the study as lending "strong confirmation" to a pair of 2012 studies [2,3] which concluded that clinicians, can, in most cases, identify the same cognitive impairments in a concussed athlete by using normative neurocognitive values as by comparing their post-concussion performance to individual pre-injury baselines.
Teens uniquely vulnerable to concussion?
Because the frontal areas of the brain believed to play a role in the ability to focus attention on relevant stimuli while filtering out extraneous information are among the last to develop, the study authors speculated that this region of the adolescent brain may be more susceptible to concussion and deficits may last longer in this population than older age groups.
Included among the studies they cited in support of the view that teens may be especially vulnerable was a 2012 study  in which Ellemberg and his colleagues found that adolescents displayed persistent neuropyschological deficits at least 6 months after concussion and were more sensitive to the effects of concussion than adults.
Like the current study, the authors of the 2012 study speculated that the adolescent age group may be more vulnerable to concussion effecting the frontal region of the brain responsible for working memory and executive function, which is undergoing a period of rapid growth in adolescence.
What constitutes 'full recovery'?
Commenting on the study, sports concussion neuropsychologist and MomsTEAM expert, Rosemarie Scolaro Moser, PhD. said that, "Howell and colleagues have addressed a very important issue in return to play: when is the athlete fully recovered from concussion? Although their study is small in nature and has its limitations, it is an addition to the current research that suggests that symptom report is not enough  to determine that athletes have fully recovered."
"In adults, we have typically thought that most athletes recover from uncomplicated concussion in 10 days or so. Yet, in a 2010 study (6) demonstrated that brain metabolites such as creatine and n-acetylaspartate normalized after approximately one month, even when athletes reported feeling back to normal by day 15 or earlier. We know that youth are more vulnerable to the effects of concussion. The Howell study joins others [7-11] in its call to keep kids out longer than is current practice."
"All the more reason to not rush kids back to school or sports and to give their brains time to heal and restabilize. Thus, concussion healthcare professionals need to advocate for these athletes to provide them with the appropriate medical leave and academic accommodations, even in the face of insistent parents, coaches, and school personnel who may want to rush them back to their usual activity," says Moser.
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Posted June 5, 2013; revised June 8, 2013 to include Dr. Moser's comments; revised further on June 17, 2013 to reflect Dr. Ellemberg's comments and include studies at footnotes 2 & 3.