CELLULAR SUBSTRATES AND LAMINAR PROFILE OF SLEEP K-COMPLEX

We describe the cellular mechanisms that underlie the generation of th e K-complex, a major grapho-element of sleep electroencephalogram in h umans. First we demonstrate the similarity between K-complexes recorde d during natural sleep and under ketamine-xylazine anaesthesia in cats . Thereafter, we show by means of multi-site cellular and field potent ial recordings that K-complexes are rhythmic at frequencies of less th an 1 Hz (mainly 0.5-0.9 Hz) and that they are synchronously distribute d over the whole cortical surface as well as transferred to the thalam us. The surface K-complex reverses its polarity at a cortical depth of . about 0.3 mm. Al the cortical depth, the K-complex is made of a shar p and high-amplitude negative deflection that reflects cellular depola rization, often preceded by a smaller-amplitude, positive slow-wave re flecting cellular hyperpolarization. The sharp component of the K-comp lex may lead to a spindle sequence and/or to fast (mainly 20-50 Hz) os cillations. K-complexes appear spontaneously or triggered by cortical or thalamic stimulation, and they arise within cortical networks. We s uggest that K-complexes, either in isolation or followed by a brief se quence of spindle waves, are the expression of the spontaneously occur ring, cortically generated slow oscillation. (C) 1997 IBRO. Published by Elsevier Science Ltd.