The reduction in intrinsic excitability in fosGFP+ cells may be a homeostatic adjustment to limit participation of these neurons in positive feedback loops that might otherwise lead to epileptic-like activity. This may be an intermediate step in hobbling highly active cells, in order to make way for a new population of cells to step in and take their place; alternatively, the suppressed input-output function may represent a new set-point for a stable subset of highly-active

Kinase Inhibitor Library mw neurons. It has been controversial whether there is structure that repeats itself during episodes of spontaneous activity. The search for recurrent motifs of activity has been evaluated at the levels of patterns of EPSCs received by a single cell or in the temporal pattern of spikes in neurons across epochs of activity (Ikegaya et al., 2004, Ikegaya et al., 2008, Luczak Vorinostat nmr et al., 2007 and Mokeichev et al., 2007). Previous analyses may have inadvertently focused on the specific temporal dynamics of these motifs, when in fact the precise sequence of neuronal activation is less conserved than the particular cells that are recruited over time. In other words, the singers may be more conserved than the song. Although the absolute number of neurons that exhibited a direct synaptic connection was low, it is notable that in all cases synaptically connected pairs were fosGFP+ neurons receiving input from other fosGFP+ neurons. Consistent with this,

other studies have shown that coactive neurons are more likely to share strong synaptic connections (Yoshimura

et al., 2005). Neurons transform synaptic input into spikes, and it is well accepted that the information encoded by a cell is determined almost exclusively by its firing output. Neurons that fire more 17-DMAG (Alvespimycin) HCl are thus likely to convey more information within a neural circuit. In addition, neurons that fire earlier during a stimulus are thought to convey more information than neurons firing later (Johansson and Birznieks, 2004 and VanRullen et al., 2005). Although it has been disputed whether rate codes or timing codes are more important, fosGFP+ cells show both a higher rate of firing and earlier recruitment during network activation and as such their spikes may carry more information than other neurons. These data do not resolve the questions of whether neural activity leads to the development of a synaptically connected cell assembly (i.e., neural activity is the independent variable) or whether this population of fos-expressing neurons is developmentally specified (and neural activity might be the dependent variable linking this subpopulation). However, the dynamic network properties of these cells indicate that a subpopulation of highly active neurons may dominate the way information is transmitted across the neocortex. Because these cells may constitute the neural substrate of “sparse coding” in the cerebral cortex (Wolfe et al.