Variability in Stroop task performance and functional activation among a small brain-injured group

Genetic polymorphisms and traumatic brain injury: the contribution of individual differences to recovery

Recovery after Traumatic Brain Injury (TBI) is variable, even for patients with similar severity of brain injury. Recent research has highlighted the contribution that genetic predisposition plays in determining TBI outcome. This review considers the potential for genetic polymorphisms to influence recovery of cognitive and social processes following TBI. Limitations and considerations that researchers should make when assessing the potential impact of polymorphisms on TBI outcome are also discussed. Understanding the genetic factors that support neuroplasticity will contribute to an understanding of the variation in outcome following injury and help to identify potential targets for rehabilitation.

Lack of long-term fMRI differences after multiple sports-related concussions

INTRODUCTION

Mild traumatic brain injury (mTBI) or concussion has been acutely associated with several cognitive symptoms, including deficits in response inhibition, working memory and motor performance. The pervasiveness of these cognitive symptoms has been more controversial. The effects of multiple concussions on neuropsychological functioning and brain activation following at least 6-months post-mTBI were examined.

METHODS

Twenty right-handed male athletes with a history of at least two concussions and 20 age/pre-morbid IQ/athletic-experience matched controls underwent neuropsychological assessment and fMRI scanning where they performed versions of a colour-word Stroop interference task, an operation-span working memory task and a finger-tapping task.

RESULTS

The Attention index score on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was lower for the concussion group, but only at liberal statistical threshold. Total RBANS score approached statistical significance. Reaction time during neurobehavioural tasks was similar across groups, but accuracy was reduced in the concussed group on the working memory task. Despite expected activation patterns within each group, there were no group differences in neural activation on any functional tasks using either whole-brain or ROI-specific analyses at liberal statistical thresholds.

CONCLUSION

There were minimal differences between the two closely matched groups. Results point to the relative plasticity of younger adults' cognitive abilities following concussion.

Genetic polymorphisms influence recovery from traumatic brain injury

Traumatic brain injury (TBI) is a major public health concern in both civilian and military populations. Recently, genetics studies have begun to identify individual differences in polymorphisms that could affect recovery and outcome of cognitive and social processes following TBI. This review considers the potential for polymorphisms to influence six specific cognitive and social functions, which represent the most prominent domains of impairment following TBI: working memory, executive function, decision making, inhibition and impulsivity, aggression, and social and emotional function. Examining the influence of polymorphisms on TBI outcome has the potential to contribute to an understanding of variations in TBI outcome, aid in the triaging and treatment of TBI patients, and ultimately lead to targeted interventions based on genetic profiles.

Disturbed cortico-subcortical interactions during motor task switching in traumatic brain injury

The ability to suppress and flexibly adapt motor behavior is a fundamental mechanism of cognitive control, which is impaired in traumatic brain injury (TBI). Here, we used a combination of functional magnetic resonance imaging and diffusion weighted imaging tractography to study changes in brain function and structure associated with motor switching performance in TBI. Twenty-three young adults with moderate-severe TBI and twenty-six healthy controls made spatially and temporally coupled bimanual circular movements. A visual cue signaled the right hand to switch or continue its circling direction. The time to initiate the switch (switch response time) was longer and more variable in the TBI group and TBI patients exhibited a higher incidence of complete contralateral (left hand) movement disruptions. Both groups activated the basal ganglia and a previously described network for task-set implementation, including the supplementary motor complex and bilateral inferior frontal cortex (IFC). Relative to controls, patients had significantly increased activation in the presupplementary motor area (preSMA) and left IFC, and showed underactivation of the subthalamic nucleus (STN) region. This altered functional engagement was related to the white matter microstructural properties of the tracts connecting preSMA, IFC, and STN. Both functional activity in preSMA, IFC, and STN, and the integrity of the connections between them were associated with behavioral performance across patients and controls. We suggest that damage to these key pathways within the motor switching network because of TBI, shifts the patients toward the lower end of the existing structure-function-behavior spectrum.

Stroop effects in persons with traumatic brain injury: selective attention, speed of processing, or color-naming? A meta-analysis

The color word Stroop test is the most common tool used to assess selective attention in persons with traumatic brain injury (TBI). A larger Stroop effect for TBI patients, as compared to controls, is generally interpreted as reflecting a decrease in selective attention. Alternatively, it has been suggested that this increase in Stroop effects is influenced by group differences in generalized speed of processing (SOP). The current study describes an overview and meta-analysis of 10 studies, where persons with TBI (N = 324) were compared to matched controls (N = 501) on the Stroop task. The findings confirmed that Stroop interference was significantly larger for TBI groups (p = .008). However, these differences may be strongly biased by TBI-related slowdown in generalized SOP (r² = .81 in a Brinley analysis). We also found that TBI-related changes in sensory processing may affect group differences. Mainly, a TBI-related increase in the latency difference between reading and naming the font color of a color-neutral word (r² = .96) was linked to Stroop effects. Our results suggest that, in using Stroop, it seems prudent to control for both sensory factors and SOP to differentiate potential changes in selective attention from other changes following TBI.