Saturday, February 23, 2008
Overtraining: You Can Learn Too Much
Naps may be helpful for learning tasks other than those involving movement (see earlier note on work by Korman et al.).* An early study on the effects of napping had developed a useful texture discrimination task in which a visual display of horizontal bars has superimposed on it a brief display of three diagonal bars, followed by a blank screen, and then by a mask. The interval between the target and the mask is varied and the interval needed to achieve 80% correct responses is used as a measure of perceptual ability and working memory.
After a single training session, performance on this task improves only after subjects have had a normal night's sleep after the day's training. To be effective, a normal amount of dream sleep, which occurs mostly in early morning, is needed.
In a follow up study by another investigator, subject performance unexpectedly deteriorated if they were given 60-minute training sessions four times at regular intervals on the same day. In other words, the more the subjects were trained, the poorer they performed. However, this interference did not occur if subjects were allowed to nap for 30-60 minutes between the second and third sessions.
It is hard to explain why over-training disrupts performance, but one has to suspect that as training trials are repeated the information starts to interfere with memory consolidation, perhaps because of boredom or fatigue in the neural circuits that mediate the learning. Napping must have a restorative function that compensates for the negative effects of overtraining. What all this suggests to me is that memory consolidation would be optimized if learning occurred in short sessions that are repeated but only with intervening naps and on different days with regular night-time sleep. In other words, repeating long study periods in the same day on the same task can be counter-productive. This is yet another reason why students should not cram-study for exams. Learning should be optimized by rehearsing the same learning material on separate days where normal sleep occurred each night.
See my book on what science reveals about improving everyday memory. I also give seminars and workshops.
Maquet, P. et al. 2002. Be caught napping: you're doing more than resting your eyes.Nature Neuroscience. 5 (7); 618-619.
Mednick, Sara, et al. 2002. The restorative effect of naps on perceptual deterioration.Nature Neuroscience. 5 (7): 677-681.