The cerebral cortex generates spontaneous activity in the form of a slow rhythm while maintained in vitro ^[1]. This activity is organized in alternating up and down states similarly to the cortical activity occurring during anesthesia and slow wave sleep ^[2]. Different studies of conductance suggest that there is an excitatory / inhibitory balance during up states, although some give a predominant role to inhibition. Previous results from our laboratory suggest that the accumulation of excitatory and inhibitory events at the beginning of up states is remarkably synchronized in the cortex both in vitro and in vivo ^[3]. The same pattern prevails during the transition from up to down states. The absolute number of detected synaptic events is also compatible with excitation and inhibition being well balanced during up states (Compte et al., Springer, 2009, in press). In this seminar I will also present how the progressive blockade of inhibition affects different properties of up states as well as their propagation rate, in an attempt to understand how inhibition modulates cortical spontaneous activity.

1. Sanchez-Vives, M.V. and D.A. McCormick, Cellular and network mechanisms of rhythmic recurrent activity in neocortex. Nat Neurosci, 2000. 3(10): p. 1027-34.
2. Steriade, M., A. Nunez, and F. Amzica, A novel slow (< 1 Hz) oscillation of neocortical neurons in vivo: depolarizing and hyperpolarizing components. J Neurosci, 1993. 13(8): p. 3252-65.
3. Compte, A., Reig, R., Descalzo, V.F., Harvey, M. A., Puccini, G.D., and Sanchez-Vives, M. V. (2008). Spontaneous high-frequency (10-80 Hz) oscillations during up states in the cerebral cortex in vitro. J Neurosci 28, 13828-13844.