Slow waves during sleep in crayfish. Origin and spread.

Previous results show that when unrestrained crayfish sleep, the electrical activity of the brain changes from multiple spikes (frequencies above 300 Hz) on a flat baseline to continuous slow waves at a frequency of 15-20 Hz. To study the temporal organization of such activity, we developed a tethered crayfish preparation that allows us to place electrodes on visually identified regions of the brain. Recording the electrical activity of different brain areas shows that when the animal is active (awake), slow waves are present only in the central complex. However, simultaneously with the animal becoming limp (sleeping), slow waves spread first to deuto- and then to protocerebrum, suggesting that the central complex of the crayfish brain acts as the sleep generator.