Spontaneous Rhythmic Activity in the Adult Cerebral Cortex In Vitro

The cerebral cortex in vivo generates different patterns of rhythmic activities with frequency rates ranging from below 1 Hz to fast frequencies well above 10 Hz. Some of these activities occur in the absence of external input and are a consequence of recurrent connectivity within the cortical network. The cerebral cortex in vitro maintains its recurrent connectivity, at least partly, and thus is able to generate some spontaneous rhythmic patterns as far as there is a certain level of intrinsic excitability in the network. An artificial cerebrospinal fluid (ACSF) with an ionic composition that mimics that in situ (Sanchez-Vives and McCormick, Nature Neuroscience. 3:1027, 2000) provides sufficient excitatory drive for the cortical network in vitro to generate not only slow (<1 Hz) rhythmic activity similar to the one that occurs during slow-wave sleep but also fast rhythms (10–80 Hz). Here, the methods and techniques used to prepare and study active cortical slices from adult animals are described, as well as the importance of methodological variables like temperature and oxygenation.