Date of Award
Doctor of Philosophy
Cognitive impairment is the most frequent cause of disability in humans following traumatic brain injury (TBI), yet the behavioral tasks used to assess cognitive behavior in rodent models of brain injury are underrepresented in the field. Additionally, few of these tasks have been used to assess behavior across degrees of injury severity. The goal of the present study was to compare four behavioral tasks commonly used in the field in frontally-injured rats with both mild and moderate-to-severe brain injuries. At the start of the study, rats were assigned to two of the following behavioral tasks: Dig scent discrimination (Dig) task, novel object recognition (NOR) task, Morris water maze (MWM), and passive avoidance (PA) task. Four days prior to injury, Dig rats were trained to dig in unscented sand and MWM rats were trained to locate a hidden platform positioned in the northeast quadrant of the MWM. Following training, bilateral controlled cortical impact injuries were induced (mild bilateral frontal TBI, moderate-to-severe bilateral frontal TBI, or non-injured, sham). Following a seven day recovery period, rats were tested on the two assigned behavioral tasks. Following testing, linear mixed effects modeling was performed assessing performance differences on the four tasks as a function of injury (injured vs. non-injured), injury severity (mild TBI vs. moderate-to-severe TBI), and task interaction. The results indicated that, while all four behavioral tasks were effective at assessing injury, some of the tasks were more effective at differentiating between injury severities than others. Specifically, the Dig task and MWM were effective at differentiating between rats with mild TBIs and rats with moderate-to-severe TBIs. Interactions between tasks also occurred such that Dig rats also assigned to the NOR task had significantly higher learning curves on the scent discriminations. The results from the current study indicate that all four behavioral tasks have the potential to assess cognitive impairment after TBI. However, these results are only a beginning. More work is needed before we can fully understand the efficacy of each of these tasks as behavioral assessment measures for cognitive functioning after TBI.
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