Individual aged rats are impaired on repeated reversal due to loss of different behavioral patterns

Aged rodents compared to young rodents are impaired in making repeated reversals and more variable in performance on many tasks. In the present study, a comparison of ten aged (21 months) and 10 young (3 months) Sprague-Dawley rats on a repeated spatial discrimination reversal water escape task revealed that the deficient and variable performance of the aged rats was due to the aged animals developing deficits in different behavioral patterns that were necessary to perform the task. Individual aged rats had deficits in inhibiting an unlearned first choice tendency (perseveration), repeating a first choice that lead to escape on the preceding trial (win-stay deficit) or inhibiting a first choice that lead to confinement and delayed escape on the preceding trial (lose-shift deficit). Because the aged animals were deficient on one or more of the necessary behavioral processes, as a group they were deficient on the repeated reversal task. However, because the aged rats differed on the specific behavioral process(es) on which they were deficient, when evaluated on any one process they were more variable than were the younger rats.