Working memory deficits following traumatic brain injury in the rat.

This study was designed to examine working memory following fluid-percussion traumatic brain injury (TBI) using the Morris water maze (MWM). Rats were injured (n = 9) at a moderate level of central fluid percussion injury (2.1 atm) or were prepared for injury but did not receive a fluid pulse (sham injury) (n = 10). On days 11-15 postinjury, working memory was assessed using the MWM. Each animal received 8 pairs of trials per day. For each pair of trials, animals were randomly assigned to one of four possible starting points and one of four possible escape platform positions. On the first trial of each pair, rats were placed in the maze facing the wall and were given 120 sec to locate the hidden escape platform. After remaining on the goal platform for 10 sec, they were placed back into the maze for the second trial of the pair. The platform position and the start position remained unchanged on this trial. After the second trial, the animal was given a 4 min intertrial rest. Between pairs of trials, both the start position and the goal location were changed. Analyses of the latency to reach the goal platform indicated that sham-injured animals performed significantly better on the second trial than on the first trial of each pair. However, injured animals did not significantly differ between first and second trial goal latencies on any day. These results indicate that injured animals have a profound and enduring deficit in spatial working memory function on days 11-15 after TBI.