Scopolamine impairs spatial working memory in the radial maze: an analysis by error type and arm choice.

The effects of scopolamine hydrobromide on performance in uninterrupted and delayed radial maze trials were studied in the rat. In addition to defining errors as incorrect arm entries, errors were defined by incorrect nose pokes in a food trough and were summed across the number of correct choices remaining. The average time elapsed from arm entry to nose poke was also calculated as a new measure of motivation and mobility. Working memory errors increased significantly following scopolamine injection in the uninterrupted trials and occurred significantly more often before the last correct choice. Errors in nonbaited arms during the last portion of a 3-h delay task increased significantly following scopolamine injection both before and after the first portion of the task and occurred more often before the last correct choice. However, nonbaited errors occurred more readily and at lower doses when scopolamine was injected 20 min before the onset of the task than when scopolamine was injected immediately after the completion of the first portion of the task. These data indicate that scopolamine affects current working memory and specifically affects acquisition more than consolidation of working memory.