Cellular Bases of Rhythmic, Recurrent Activity in the Cerebral Cortex
Mavi Sanchez-Vives and David A. McCormick
Section of Neurobiology
Yale University School of Medicine
Introduction
The brain is constantly active, even during deep sleep. In the cerebral cortex,
this spontaneous activity (activity that is not obviously driven by a sensory input
or a motor command) often occurs as periodic, rhythmic discharges. One form of
rhythmic cortical activity that recently has been investigated extensively in vivo
is the so-called "SLOW OSCILLATION" (see Steriade and colleagues, references here).
The slow oscillation is characterized by periods of sustained depolarization interweaved
with periods of hyperpolarization and silence at a rate of between once every 10 seconds
to approximately once per every 2 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, you guessed it, 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!
Figure 1. 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. 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.
The slow oscillation is generated in the Cerebral Cortex, since removal of the thalamus
does not block the slow oscillation and isolation of slabs of cortex retain this
activity (reference). However, previous investigators have not demonstrated the
slow oscillation in vitro in cortical slices. Here, we demonstrate the slow oscillation
in cortical slices maintained in vitro, and we use this preparation to demonstrate how
this activity is generated. Finally, we speculate on the functional significance of
the ability of the cerebral cortex to generate rhythmic, recurrent activity and the
possible functional significance of spontaneous activity in general.
For more information, please see the following publication:
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.
