One Example of Intracortically Generated Periods of Persistent Activity Occurs as the Slow Oscillation During Sleep
One example of rapid changes in neuronal activity and excitability that can be readily analyzed with modern techniques is the generation of the so-called slow oscillation in the cerebral cortex during sleep (see Figure 4 below). The slow oscillation is characterized by periods of sustained depolarization interweaved with periods of hyperpolarization and silence at a rate of between once every 2-10 seconds. The depolarized state is associated with low frequency neuronal firing and is termed the UP state, while the hyperpolarized state is referred to as the DOWN state. The frequent transitions between the UP and DOWN state can make the membrane potential of the cortical neuron appear as a single channel recording, even though the slow oscillation is generated by the interaction of thousands of cells!
Slow oscillation in vivo and its disruption by stimulation of the brainstem. The top trace is an intracellular recording from a cortical pyramidal cell during the slow oscillation in an anesthetized animal. The bottom trace is the electrocorticogram (EcoG). Repetitive stimulation of the brainstem results in activation of the EEG and suppresses the "down" state of the slow oscillation. From Steriade, M Amzica, F, Nunez A. 1993. Cholinergic and noradrenergic modulation of the slow (approximately 0.3 Hz) oscillation in neocortical cells. J. Neurophysiol. 70: 1385-1400.
We have developed a slice preparation that also exhibits UP and DOWN states of activity (Sanchez-Vives and McCormick, 2000) and here we have utlized this behaving slice to investigate how local networks in the cortex may generate periods of balanced, low frequency action potential activity. We demonstrate that a basic operation of the cortex is the generation of multiple states of activity through a propotionality and balance between recurrent excitation and inhibition.
For more information, please see the following publication: Shu, Y-S., Hasenstaub, A., and McCormick, D.A. (2003) Turning on and off recurrent, balance cortical activity. Nature 423: 288-293. Sanchez-Vives, M.V. and McCormick, D.A. (2000) Cellular and network mechanisms of rhythmic, recurrent activity in the cerebral cortex. Nature Neuroscience 3: 1027-1034.