Origin of slow cortical oscillations in deafferented cortical slabs

An in vivo preparation has been developed to study the mechanisms underlyin g spontaneous sleep oscillations. Dual and triple simultaneous intracellula r recordings were made from neurons in small isolated cortical slabs (10 mm x 6 mm) in anesthetized cats. Spontaneously occurring slow sleep oscillati ons, present in the adjacent intact cortex, were absent in small stabs. How ever, the isolated slabs displayed brief active periods separated by long p eriods of silence, up to 60 s in duration. During these silent periods, 60% of neurons showed non linear amplification of low-amplitude depolarizing a ctivity. Nearly 40% of the cells, twice as many as in intact cortex, were c lassified as intrinsically bursting. In cortical network models based on Ho dgkin-Huxley-like neurons, the summation of simulated spontaneous miniature excitatory postsynaptic potentials was sufficient to activate a persistent sodium current, initiating action potentials in single neurons that then s pread through the network. Consistent with this model, enlarging the isolat ed cortical territory to an isolated gyrus (30 mm x 20 mm) increased the pr obability of initiating large-scale activity. In these larger territories, both the frequency and regularity of the slow oscillation approached that g enerated in intact cortex. The frequency of active periods in an analytical model of the cortical network accurately predicted the scaling observed in simulations and from recordings in cortical slabs of increasing size.