Why do we sleep?

Slow-wave sleep consists in slowly recurring waves that are associated with a large-scale spatio-temporal synchrony across neocortex. These slow-wave complexes alternate with brief episodes of fast oscillations, similar to th e sustained fast oscillations that occur during the wake state. We propose that alternating fast and slow waves consolidate information acquired previ ously during wakefulness. Slow-wave sleep would thus begin with spindle osc illations that open molecular gates to plasticity, then proceed by iterativ ely 'recalling' and 'storing' information primed in neural assemblies. This scenario provides a biophysical mechanism consistent with the growing evid ence that sleep serves to consolidate memories. (C) 2000 Elsevier Science B .V. All rights reserved.