Applicability of neural reserve theory in mild traumatic brain injury

Feasibility of using normobaric hypoxic stress in mTBI research

Studies of mild traumatic brain injury (mTBI) recovery generally assess patients in unstressed conditions that permit compensation for impairments through increased effort expenditure. This possibility may explain why a subgroup of individuals report persistent mTBI symptoms yet perform normally on objective assessment. Accordingly, the development and utilization of stress paradigms may be effective for enhancing the sensitivity of mTBI assessment. Previous studies, discussed here, indirectly but plausibly support the use of normobaric hypoxia as a stressor in uncovering latent mTBI symptoms due to the overlapping symptomatology induced by both normobaric hypoxia and mTBI. Limited studies by our group and others further support this plausibility through proof-of-concept demonstrations that hypoxia reversibly induces disproportionately severe impairments of oculomotor, pupillometric, cognitive and autonomic function in mTBI individuals.

Long-term consequences: effects on normal development profile after concussion

Each year in the United States, approximately 1.7 million people are diagnosed with a traumatic brain injury (TBI), about 75% of which are classified as mild TBIs or concussions. Although symptoms typically resolve in a matter of weeks, both children and adults may suffer from postconcussion syndrome for months or longer. A progressive tauopathy, chronic traumatic encephalopathy, is believed to stem from repeated brain trauma. Alzheimer-like dementia, Parkinsonism, and motor neuron disease are also associated with repetitive brain trauma. Effective diagnoses, treatments, and education plans are required to reduce the future burden and incidence of long-term effects of head injuries.

Validation of the Abbreviated Westmead Post-traumatic Amnesia Scale: a brief measure to identify acute cognitive impairment in mild traumatic brain injury

OBJECTIVE

To validate the use of the Abbreviated Westmead Post-traumatic Amnesia Scale (A-WPTAS) in the assessment of acute cognitive impairment in mild traumatic brain injury (mTBI).

METHODS

Data previously collected from 82 mTBI and 88 control participants using the Revised Westmead Post-traumatic Amnesia Scale (R-WPTAS) was converted to A-WPTAS scores and pass/fail classifications were calculated for both scales.

RESULTS

The proportion of failures on the R-WPTAS and the A-WPTAS did not differ and a similar number of mTBIs were classified on each. For mTBIs the relationship between the independent memory test and a pass/fail classification was the same for both scales. Bivariate logistic regressions revealed that mTBIs, relative to controls, were around 8 times more likely to fail the assessment (R-WPTAS: 95% CI: 3.70-18.87; A-WPTAS: 95% CI: 3.70-20.14). As verbal learning improved the likelihood of failure was reduced. Greater education was associated with a decreased likelihood of failure. The relationship between education and a fail performance was not sustained when education was adjusted for the effect of age, prior mTBI, blood alcohol level, injury status, verbal learning, and morphine administration.

CONCLUSIONS

The A-WPTAS is a valid measure. The A-WPTAS may reduce the risk of failing to classify patients with mTBI by identifying and documenting acute cognitive impairment.

A longitudinal proton magnetic resonance spectroscopy study of mild traumatic brain injury

Despite the prevalence and impact of mild traumatic brain injury (mTBI), common clinical assessment methods for mTBI have insufficient sensitivity and specificity. Moreover, few researchers have attempted to document underlying changes in physiology as a function of recovery from mTBI. Proton magnetic resonance spectroscopy (¹H-MRS) was used to assess neurometabolite concentrations in a supraventricular tissue slab in 30 individuals with semi-acute mTBI, and 30 sex-, age-, and education-matched controls. No significant group differences were evident on traditional measures of attention, memory, working memory, processing speed, and executive skills, though the mTBI group reported significantly more somatic, cognitive, and emotional symptoms. At a mean of 13 days post-injury, white matter concentrations of creatine (Cre) and phosphocreatine (PCre) and the combined glutamate-glutamine signal (Glx) were elevated in the mTBI group, while gray matter concentrations of Glx were reduced. Partial normalization of these three neurometabolites and N-acetyl aspartate occurred in the early days post-injury, during the semi-acute period of recovery. In addition, 17 mTBI patients (57%) returned for a follow-up evaluation (mean = 120 days post-injury). A significant group × time interaction indicated recovery in the mTBI group for gray matter Glx, and trends toward recovery in white matter Cre and Glx. An estimate of premorbid intelligence predicted the magnitude of neurometabolite normalization over the follow-up interval for the mTBI group, indicating that biological factors underlying intelligence may also be associated with more rapid recovery.

Material-specific difficulties in episodic memory tasks in mild traumatic brain injury

The study examines acute, material-specific secondary memory performance in 26 patients with mild traumatic brain injury (MTBI) and 26 healthy controls, matched on demographic variables and indexes of crystallized intelligence. Neuropsychological tests were used to evaluate primary and secondary memory, executive functions, and verbal fluency. Participants were also tested on episodic memory tasks involving words, pseudowords, pictures of common objects, and abstract kaleidoscopic images. Patients showed reduced performance on episodic memory measures, and on tasks associated with visuospatial processing and executive function (Trail Making Test part B, semantic fluency). Significant differences between groups were also noted for correct rejections and response bias on the kaleidoscope task. MTBI patients' reduced performance on memory tasks for complex, abstract stimuli can be attributed to a dysfunction in the strategic component of memory process.