SELECTIVE COGNITIVE IMPAIRMENT FOLLOWING TRAUMATIC BRAIN INJURY IN RATS

Impairment of cognitive abilities is a frequent and significant sequel ae of traumatic brain injury (TBI). The purpose of this experiment was to examine the generality of the cognitive deficits observed after TB I. The performance of three tasks was evaluated. Two of the tasks (pas sive avoidance and a constant-start version of the Morris water maze) were chosen because they do not depend on hippocampal processing. The third task examined was the standard version of the Morris water maze which is known to rely on hippocampal processing. Rats were either inj ured at a moderate level (2.1 atm) of fluid percussion brain injury or surgically prepared but not injured (sham-injured control group). Nin e days after fluid percussion injury, injured (n = 9) and sham-injured rats (n = 8) were trained on the one-trial passive avoidance task wit h retention assessed 24 h later. On days 11-15 following injury, injur ed (n = 9) and sham-injured (n = 8) rats were trained on a constant-st art Version of the Morris water maze that has the animals begin the ma ze from a fixed start position on each trial. Additional injured (n = 8) and sham-injured (n = 8) animals were trained on days 11-15 after i njury on the standard (i.e. using variable start positions) version of the Morris water maze. The results of this experiment revealed that p erformance of the passive avoidance and the constant-start Version of the Morris water maze were not impaired by fluid percussion TBI. Howev er, performance on a task that is usually disrupted by hippocampal dam age (variable-start version of the Morris water maze) was significantl y impaired by TBI. Thus, the hippocampus appears to be selectively dam aged following TBI.