Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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Monday, 31.01.2011 17 c.t.

Criticality in Cortical Neurons: Up states are critical, Down states are subcritical

by Prof. Dr. Ernst Niebur
from Mind/Brain Institute, Johns Hopkins University, Baltimore, MD, USA

Contact person: Florentin Wörgötter


Seminarraum Haus 2, 4. Stock (Bunsenstr.)


During sleep, under anesthesia and in vitro, cortical neurons in sensory, motor, association and executive areas fluctuate between Up and Down states (UDS) characterized by distinct membrane potentials and spike rates. While Down states are quiescent, Up state activity resembles that of REM sleep and wakefulness, suggesting similar network processing. Another network phenomenon observed in preparations similar to those that exhibit UDS, such as anesthetized rats, brain slices and cultures devoid of sensory input, as well as awake monkey cortex, is self-organized criticality (SOC). This is characterized by activity "avalanches" whose size distributions obey a power law with critical exponent of about -3/2 and branching parameter near unity. We report an intimate connection between the two phenomena, SOC and UDS. We show analytically that networks of leaky integrate-and-fire neurons with short-term synaptic depression typically have 2 stable activity levels corresponding to UP and Down states, and that Up states are critical and Down states are subcritical. Our analytical results are confirmed by simulations of networks with different connectivity structures which also switch spontaneously between Up and Down states.

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