Finding Our Way Through the Fog of Concussion Research

Neuropsychologists and the general public have become increasingly aware of the prevalence and potential consequences of concussions. With this rising awareness, a practicing clinical neuropsychologist may see more people with concussions knocking at the office door but lack familiarity with the existing research on concussion.

This practitioner may head to Google Scholar, typing in "concussion," "cognition," return to play," and other keywords to become familiar with the existing research, hoping to figure out, for example, the expected duration of recovery, the sequelae of multiple head injuries, and the cognitive domains affected by the injury.

To the dismay of the clinician, the search results in thousands of hits, including case studies, empirical articles, and meta-analyses, all reporting results confounded by the nature of the injury (e.g., sports related, falls, car crashes), the design of the research (e.g., cross-sectional, prospective), and the selected outcomes (e.g., executive functions, memory). Even the meta-analyses, intended to synthesize and clarify the literature, report some inconsistent findings, and — given that more than 10 meta-analyses on concussion have been published to date — the clinician has trouble deciding which one to trust.

To help this overwhelmed clinician, Justin E. Karr, Corson N. Areshenkoff, and Mauricio A. Garcia-Barrera (2014) just published a systematic review of meta-analyses in the May issue of Neuropsychology. They evaluated the common and diverse contributions of recent meta-analyses to furthering the scientific understanding of cognitive recovery following concussions. Each meta-analysis differed in its scope, with some examining only sports-related concussions and others evaluating concussions in the general population, known as mixed-mechanism concussions.

For analysis, meta-analyses rely on effect sizes that quantify the difference between the concussed group and control group in units of standard deviations, with a larger, more positive effect size indicating a worse average performance by participants with concussion. The meta-analyses differed significantly in their overall effect sizes, with sports-related concussion effects ranging from medium to large (range: .40–.81) and mixed-mechanism concussion effects ranging from virtually zero to medium (range: .07–.61).

Multiple design and sample characteristics explain the variability in these reported effect sizes, resulting in four key conclusions to facilitate research, practice, and policy-related decision making:

• Cognitive recovery following concussion occurs for the majority of individuals by 90 days postinjury, with a more rapid recovery window observed among athletes (i.e., 7 days).
• Among participant characteristics, greater age and level of education, along with belonging to the male gender, resulted in smaller cognitive deficits within 14 days of injury.
• These recovery expectations derive from an average estimate across all cognitive abilities, but cognitive domains vary in recovery trajectories. Effect sizes divided by cognitive domain varied significantly across meta-analyses (e.g., effect sizes for executive functions ranged from -.11 to .72), indicating a limited scientific understanding of postconcussion impairment on the basis of cognitive construct.
• An early meta-analysis on concussion labeled it a frontal-executive injury. However, more recent reviews have found much smaller effects for executive functions, although these self-regulatory abilities appear to be most sensitive to multiple concussion and second-most sensitive to head injury exposure (e.g., heading frequency in soccer), potentially implicating executive dysfunction as a marker of repeated minor head injury.

These conclusions, among others reported within the article itself, provide a snapshot of the existing research on concussion. Although these statements can refresh and update clinicians through one summative article, the neuropsychological research on concussions remains a dynamic and burgeoning field.

Scientists have yet to explore multiple moderators that potentially impact the cognitive sequelae of concussion (e.g., location of impact, injury mechanism). Moving forward, future researchers should further examine these variables within their designs, helping predict individual differences in recovery on the basis of the characteristics of both the individual and the injury itself.

Citation:
Karr, J. E., Areshenkoff, C. N., & Garcia-Barrera, M. A. (2014). The neuropsychological outcomes of concussion: A systematic review of meta-analyses on the cognitive sequelae of mild traumatic brain injury. Neuropsychology, 28, 321–336. doi: 10.1037/neu0000037

Note: This article is in the Health Psychology & Medicine topic area. View more articles in the Health Psychology & Medicine topic area.