POSTER PRESENTATION Open Access Two different mechanisms alternate during

Brain states can be classified as synchronized (large amplitude low frequency oscillations) or desynchronized (small amplitude high frequency activity). [1] Synchro-nized states are marked by UP states/phases character-ized by global spiking and DOWN states/phases are characterized by global silence in the cortex. In awake animals, desynchronized states are associated with pro-cessing sensory input and behavior while synchronized states are associated with quiet idling conditions. During sleep, REM is considered desynchronized and slow-wave sleep is considered synchronized. While desynchronized brain states are often triggered by various kinds of neu-ronal input to cortical areas, the exact mechanism at work during synchronized brain states is still unclear. In particular, there are two hypothesized mechanisms for the slow oscillation during slow-wave sleep: UP phases can be produced either by traveling neocortical waves or a thalamo-cortical loop [2-4]. In our study, applying independent component analysis (ICA) to recordings from rat neocortex reveals two dif-ferent mechanisms during synchronized activity. The mechanisms are distinguished by two key neural sources identified by ICA: a strong broad source centered in layer 5 (BL5) and an apparent sub-cortical source producing clock-like oscillations which resemble hippocampal theta oscillations (SUB). The BL5-state often resembles corti-cally generated oscillations: UP phases are initiated in deeper layers akin to traveling neocortical waves and the oscillation is relatively slow. The SUB-state can resemble thalamo-cortically generated oscillations: UP phases are initiated in layer 4 as well as deeper layers and the oscilla-tion is faster. These findings suggest that both hypothe-sized mechanisms for the slow oscillation are at work in the cortex- in alternation