A hierarchy of neurobehavioral tasks discriminates between mild and moderate brain injury in rats

Behavioral analysis commonly assesses cognitive deficits in rodents following traumatic brain injury (TBI). We examined rats that received sham, mild or moderate injury in the controlled cortical impact model of TBI. The rats were tested in a novel hierarchy of four behavioral tasks with increasing cognitive demand. All three groups had similar performance on the first two phases of training: open field exploration and passive place avoidance using a stationary shock zone on a non-rotating arena. The similar performance on the first two tasks suggested comparable sensory, motor skills and contextual memory in all three groups. In phase three, rats were tested on active place avoidance, their ability to avoid a stationary shock zone on the rotating arena. Control and mildly-injured rats learned this task within four ten-minute trials while moderately-injured animals were impaired. Moderately-injured animals were also impaired if tested 3 weeks after injury. One day after phase three, sham- and mildly-injured animals were tested on a phase four conflict active avoidance task with the shock zone shifted 180 degrees from its phase three location and mildly-injured animals were impaired. The speed in which the animals complete the four phases of testing as well as the ability to discriminate between differing injury severity suggests that this set of neurobehavioral tasks will be useful to understand cognitive deficits underlying TBI as well as a useful screening method for therapeutic drugs.