A majority of mildly brain injured patients, as well as those more severely injured, showed diminished NAA/creatine (Cr) levels in the splenium compared with normal control volunteers. The patients displaying lowered NAA/Cr in the splenium were also likely to exhibit lowered NAA/Cr in lobar white matter. Also, the levels of NAA/Cr in the splenium of normal volunteers were higher compared with those found in lobar white matter. Decreases in NAA/Cr levels in the splenium may be a marker for diffuse injury. A proton MRS examination may be particularly useful in evaluating mildly injured patients with unexplained neurological and cognitive deficits. It is concluded that MRS is a sensitive tool in detecting axonal injury.

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Disorders of visuomotor function are common following traumatic brain injury (TBI), but spatially directed visual attention has received little study in this population. 'Cancellation' testing is a common bedside method for assessing directed attention, which can provide information on how task properties influence visual scanning and search following severe TBI. Groups of 20 individuals after severe TBI and 21 healthy control subjects were matched for age and education. Participants performed finger tapping tests to assess motor speed as well as four cancellation tests employing letter and geometric figure stimuli in random and structured arrays. Control and TBI groups differed significantly on measures of accuracy, task completion time, and search quality. There was no significant effect of stimulus or array type on accuracy or time. Figure targets in a higher search quality, suggesting a right hemispheric dominance effect on these tasks. The findings support a deficit in visuomotor scanning performance in TBI beyond a purely motor effect. Interactions between stimulus and array types suggest that hemispheric cooperation is required for the optimal performance of these tasks, and that interhemispheric communication may be preferentially compromised by TBI.

The object of this study was to investigate stimulus effects and motor limitations on visuospatial performance after traumatic brain injury (TBI). Previous findings have not fully explained the basis of attentional impairments after TBI. There has been little study of the spatial aspects of attention and information processing in this group. We studied 20 patients after severe TBI and 21 healthy controls. Four random-array letter cancellation tasks, varying in number of stimuli (50 and 100) and target-to-distractor ratio (1:4 and 1:9) were employed. Performance was calculated from the number and proportion of cancelled targets, as well as time to completion. TBI subjects were slower on finger tapping and achieved lower cancellation performance scores. Both TBI subjects and controls performed better on tasks with target-to-distractor (T/D) ratios of 1:4 than on those with 1:9. There was no effect of stimulus number. We conclude that there are both quantitative (speed) and qualitative contributors to impaired visuospatial ability following TBI. Motor impairments may slow the overall cancellation performance, but the differential effect of T/D ratio in the two populations suggests that TBI impairs quality of research. Accounting for both speed and accuracy suggests increased utility for the cancellation paradigm in clinical and research assessment of visuospatial attention.

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