Study of sleep spindles in the rat: a new improvement.

The two kinds of sleep spindles, previously described in the rat, were studied in intact animals, cerveau isole preparations and unilaterally neodecorticated rats. The anterior (frontal) spindles reach their maximum during deep slow sleep, when accompanied by theta activity, during the so-called intermediate stage which occurs just before and after paradoxical sleep. This stage is extended by low doses of barbiturate and similar patterns are induced by an intercollicular transection. The anterior spindles are suppressed by unilateral nedecortication and become abortive on contralateral hemisphere. The posterior ones, larger when recorded in the dorsal hippocampus than an the occipital cortex precede the appearance of the theta activity of intermediate stage. They are absent when the theta rhythm is present, during the long-continued intermediate stage under barbiturate ad in the cerveau isole preparation; but an unilateral neodecortication does not prevent the occurrence of posterior spindles on the white matter. Thus, during deep slow sleep, the rat shows both frontal cortex spindles, fully spread out during intermediate stage, and posterior spindles, probably originating from structures implied in the theta genesis and heralding the occurrence of this rhythmic slow activity.