Abstract
Behavioral performance is the gold standard for assessing treatments designed to facilitate recovery from brain injury. Distinguishing between recovery and behavioral compensation is necessary in order to properly evaluate therapeutic efficacy, yet most current studies fail to assess the potential role of compensatory strategies on behavioral performance. The beamwalk task has been used extensively to evaluate sensorimotor ability following CNS damage. Although enhanced performance has traditionally been attributed to recovery, recent data using a modified version of the task suggest that in rats, post-operative beamwalk improvements are primarily due to behavioral compensation.The purpose of this dissertation was to evaluate the sensitivity of the modified beam relative to the traditional beam for detecting chronic sensorimotor deficits in mice. A second aim was to identify subcomponents of gait dysfunction following a moderate injury. Lastly, compensatory strategies were identified to reveal potential methods the animals' use in order to perform the beamwalk task. Video recording and foot inking measures were used to identify gait dysfunction and compensation.Results revealed more chronic sensorimotor deficits using the modified beam than with the traditional beam. Whereas post-operative mice tested on the traditional beam improved over time, mice trained on the modified beam continued to show gait deficits by using the side-attached ledges rather than walking atop the beam. Subcomponents of TBI-induced sensorimotor deficits were also revealed. Among these dysfunctions were flexion and adduction impairments. Injured animals could adduct their impaired limb when evaluated under easier testing conditions, but had significant impairments adducting when tested on a more challenging task. Thus, adduction deficits following TBI were evident dependent on task difficulty. Flexion dysfunction was also revealed as a long-lasting gait deficit, as post-operative animals had reduced ability to pull up their impaired hindlimb in order traverse the beam.In identifying compensatory strategies, the ledge was determined to be an easily measurable form of compensation. In addition, tail use was detected as an effective compensatory technique. Mice would contralaterally deviate or cling with their tails depending on the degree of task difficulty.The experiments described in this dissertation were effective in establishing the modified beam as a useful behavioral task for evaluating chronic sensorimotor deficits in the mouse. Subcomponents of gait dysfunction, flexion and adduction deficits, were identified and may be useful dependent measures in future studies. In addition, these experiments provide the first quantitative evaluation of compensatory tail use. Together, the results reveal the utility of the modified beamwalk task for detecting locomotor deficits and compensatory strategies in a mouse model of brain injury. This task could be employed for determining the efficacy of treatments designed to promote recovery following CNS injury.