Paradoxical sleep increases predict successful learning in a complex operant task.

The sleep of 16 Sprague-Dawley rats was continuously monitored both before and during task acquisition. Eight rats were exposed in turn to autoshaping, 10-response fixed-ratio (FR 10), and sequential operant (SO) tasks. They all learned the autoshaping and FR 10 tasks with equal ease. However, 4 rats were unable to solve the SO task and were labeled as slow learning (SL). The other 4 rats did learn the task and were labeled as fast learning (FL). FL rats exhibited more paradoxical sleep than either the SL group or the two control groups. The results suggest a subtle, but as yet unknown, biological difference between FL and SL rats within the Sprague-Dawley strain.