The paper has been corrected online, and we sincerely regret the errors.

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“(Neuron 74, 924–935; June 7, 2012) In the original publication of this paper, the y axis of Figure 4C was incorrectly labeled with values of 0.8, 0.6, 0.4, etc. The correct figure is displayed here, and the article has been corrected online. “
“The slow rhythmic activity that dominates the brain during sleep and anesthesia has been a fascinating topic of study since the first electroencephalographic studies of Hans Berger (1929). The large amplitude and low frequency of anesthesia-induced activity can be recorded with a high signal-to-noise ratio and has often been used to VE821 study how different populations of neurons throughout the brain interact to generate patterns of activity. A new oscillatory pattern was discovered by

Steriade and coworkers in 1993 (Steriade et al., 1993), termed the slow oscillation given its low frequency of 0.1–0.9 Hz. The slow oscillation is characterized intracellularly in cortical and thalamic cells by regularly recurring periods of depolarization and spike firing (up-states) and periods of hyperpolarization and quiescence with very little synaptic activity (down-states). The depolarizing and hyperpolarizing cycles are correlated between cortical cells across hemispheres as well as between thalamic and cortical neurons as shown by simultaneous dual intracellular

recordings in vivo and (Contreras and Steriade, IPI-145 purchase 1995; Steriade et al., 1993). During natural sleep, the slow oscillation groups the other two cardinal sleep rhythms of spindles and delta waves in a slow beating pattern (Steriade et al., 1993) observed in all mammals, including humans. The rhythm is generated intracortically as it survives removal of the thalamus in vivo (Steriade et al., 1993) and can be generated in cortical slices maintained in medium that mimics ionic concentrations observed in situ (Sanchez-Vives and McCormick, 2000). In this issue of Neuron, Stroh et al. (2013) combined imaging of population calcium (Ca2+) fluorescent signals from cortex and thalamus with optogenetic and visual stimulation in mouse in vivo to study the mechanism and spatiotemporal properties of the slow oscillation. The authors devised a method to record and stimulate brain activity by using an optical fiber that allows the excitation and recording of a fluorescent Ca2+ indicator as well as stimulation of channelrhodopsin (ChR2)-expressing neurons. Furthermore, the optical fiber allows excitation and recording of calcium signals in structures deep in the brain, such as the thalamus. To record suprathreshold activity from populations of neurons, Stroh et al.