Rouping of Brain Rhythms in Corticothalamic Systems

bstract—Different brain rhythms, with both low-frequency nd fast-frequency, are grouped within complex wave-seuences. Instead of dissecting various frequency bands of he major oscillations that characterize the brain electrical ctivity during states of vigilance, it is conceptually more ewarding to analyze their coalescence, which is due to neuonal interactions in corticothalamic systems. This concept f unified brain rhythms does not only include low-frequency leep oscillations but also fast (beta and gamma) activities hat are not exclusively confined to brain-activated states, ince they also occur during slow-wave sleep. The major actor behind this coalescence is the cortically generated low oscillation that, through corticocortical and corticothaamic drives, is effective in grouping other brain rhythms. The xperimental evidence for unified oscillations derived from imultaneous intracellular recordings of cortical and thaamic neurons in vivo, while recent studies in humans using lobal methods provided congruent results of grouping diferent types of slow and fast oscillatory activities. Far from eing epiphenomena, spontaneous brain rhythms have an mportant role in synaptic plasticity. The role of slow-wave leep oscillation in consolidating memory traces acquired uring wakefulness is being explored in both experimental nimals and human subjects. Highly synchronized sleep osillations may develop into seizures that are generated intraortically and lead to inhibition of thalamocortical neurons, ia activation of thalamic reticular neurons, which may exlain the obliteration of signals from the external world and nconsciousness during some paroxysmal states. © 2005 ublished by Elsevier Ltd on behalf of IBRO.