Effects of Concussion on Attention and Executive Function in Adolescents

David Howell; Louis Osternig; Paul Van Donkelaar; Ulrich Mayr; Li-Shan Chou

Disclosures

Med Sci Sports Exerc. 2013;45(6):1030-1037. 

In This Article

Discussion

This investigation was a longitudinal analysis of two cognitive tests which examined how attention and executive function were influenced by concussion in adolescents. The results demonstrated that executive function as assessed in both the ANT and TST was disrupted in concussed adolescents for up to 2 months after injury when compared with a healthy cohort of matched control subjects. By contrast, the alerting and orienting components of attention were not affected by concussion.

The ANT conflict effect appeared to be considerably disrupted by concussion as the injured group had difficulties ignoring irrelevant information contained in the incongruent target configurations. This resulted in significantly longer RT scores than controls for this measure throughout the testing period. These findings are consistent with those of Halterman et al.,[15] who found the ability to focus while ignoring irrelevant but conflicting stimuli was impaired up to 1 month after concussion in young adults when compared with matched controls. In the present study, this impairment was evident in the concussed adolescent group for up to 2 months postinjury. This impairment was observed for an extended period when compared with results from the clinical symptom inventory, as the resolution of symptoms typically occurred between 2 wk and 1 month after injury.

Previous reports indicate that the ANT-orienting effect was negatively affected in young adults with concussion during the first 48 h after injury.[15] In contrast, the present study detected no differences between groups at any time points for the orienting effect. This may be due to a difference in subject age, or that the current study included those whose initial testing time was up to 72 h after injury, thus extending the amount of potential initial recovery from injury. However, the difference between healthy and concussed subjects at 72 h postinjury appears to be similar to those previously reported but statistically insignificant. In addition, the lack of any differences between groups or across testing days for the alerting effect is consistent to previous findings in young adult subjects.[15] The lack of significant differences between groups in both the orienting and alerting effects may also indicate that no preexisting attentional deficits were present between healthy and concussed subjects.

Previous literature identifies the anterior cingulate cortex and prefrontal cortex regions of the brain as the areas responsible for conflict resolution.[10] The anterior cerebral structures are believed to play a role in the ability to focus attention on relevant stimuli while filtering out extraneous information.[36,37] As these frontal regions of the brain are among the last to develop,[35] this region of the adolescent brain may be susceptible to concussion and deficits may last longer in this population than older age groups.[2]

In the TST, the reaction time cost of accurately switching from one task to another was significantly greater for the concussed group than the controls throughout the 2-month testing period. Task-switching tasks have previously been shown to probe executive function by requiring subjects to flexibly plan responses in a context-dependent manner.[26] Given that efficient and accurate performance of motor skills involves reaction to and behavior produced from multiple stimuli occurring simultaneously, the task-switching paradigm may provide useful information on the demands of changing internal cognitive configurations,[25] which must be addressed during multitasking endeavors, such as in academic, job-related, and sport activities.

Executive function has been considered to be responsible for the synthesis of external stimuli and preparation of action,[24] and individuals with mTBI often struggle to maintain or appropriately allocate their attentional resources while performing one or more concurrent tasks (5–7,34). The results of this study suggest that tests which isolate components of executive function (ANT and TST) are sensitive to the effects of concussion in adolescents and reveal cognitive 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. As task switching and conflict resolution are central to any activity that involves distribution of attention, this type of testing may help to understand how well an individual will respond to such a demand when required to do so. The identification of executive function disruption may help to assist in the assessment of recovery from concussion.

In this study, both the concussed and control subjects displayed improvements in the ANT conflict effect and TST switch cost across the 2-month testing period, indicating that performance on both tasks got better with practice and/or learning. Similar practice effects were observed for the first few days of testing on the ANT conflict effect by Ishigami and Klein,[17,18] and as a consequence, they noted the need for a control group in some designs. Given the significant between-group differences and the lack of an interaction between the concussed and the control groups across the testing sessions, these tasks appear to remain sensitive to the disruptions in executive function induced by concussion for up to 2 months postinjury.

The prospective study design and strict subject inclusion criterion related to recruiting and beginning testing within 72 h after injury was a limitation of this study as it resulted in the loss of some potential concussed subjects who were unable to enroll in the study as they could not report for testing within this initial 72-h time frame. However, there was no attrition of any of the 40 subjects during testing. This study was also limited in that no subject baseline data were reported. The inclusion of individually matched healthy control subjects to which the concussed population was compared for the same testing periods countered this limitation to some extent. Although all injured subjects were considered to have sustained a mTBI (concussion) as defined by the 3rd International Statement on Concussion in Sport,[28] there undoubtedly was variability in the extent of the injury possibly due to different mechanisms of injury. This variability was mitigated by the exclusion criteria.

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