Cognitive Load in Mild Traumatic Brain Injury: A Pupillometric Assessment of Multiple Attentional Processes
Uniformed Services University of the Health Sciences Bethesda United States
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Background and Methods Individuals with a history of mild TBI may have an impaired ability to allocate sufficient neural resources necessary to complete cognitivetasks. Due to this reduced cognitive efficiency, cognitive tasks may impose greater demand, or cognitive load, on individuals with mild TBI compared to their uninjured counterparts. This is particularly relevant for specific attentional and executive function networks, as these networks are most vulnerable to injury, and may have behavioral consequences. Using pupillometric measures of cognitive load, the current study sought to test the effect of mild TBI on multiple attentional processes, including sustained tonic activation, and alerting, orienting, and controlled attention phasic activation. To test the effect of mild TBI on sustained attention, baseline pupil diameter and its variability during a sustained cued-attention task were compared between individuals with a remote history of mild TBI and uninjured controls. To test the effect of mild TBI on alerting, orienting, and controlled attention, group comparisons were made for percent change in pupil diameter relative to baseline and its variability in response to various cue-target combinations designed to index each of these three processes. Finally, the relationship between cognitive load as indexed by pupillometrics and behavior was assessed for both the mild TBI group and controls. Results The mild TBI group n25 had faster response time to controlled attention trials but were similar to controls n51 for alerting and orienting trials. Pupillometry data are mixed. They showed that the clinical sample had marginally smaller baseline pupil diameter, marginally greater baseline pupil diameter variability, and marginally greater cue-locked pupil diameter variability for controlled attention trials than controls. Moreover, a linear trend in pupil diameter variability was observed for the mild TBI group but not the control group.
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