Jaime de la Rocha, Cortical Circuit Dynamics Group, Barcelona

UP-DOWN cortical dynamics reflect stochastic state transitions in bistable cortical circuits

In the idling brain, neuronal circuits transition between periods of sustained firing (UP state) and quiescence (DOWN state). Despite the ubiquity of this pattern across many species and brain areas, the underlying mechanisms remain unclear. In this talk I will present results from the analysis and modelling of population cortical recordings during spontaneous and stimulus evoked conditions from anaesthetized rats. I will first address the role of UP-DOWN transitions generating pair-wise correlations across different brain states. I will show that the reduction of correlation accompanying brain state de-synchronization can be largely explained by a decrease in the density of the silent periods (DOWN states). Moreover, the presentation of a stimulus causes an initial drop of correlations followed by a rebound, a time course that is mimicked by the instantaneous silence density. A rate model showing fluctuation-driven transitions between a silent and an active attractor can reproduce the relation between correlation and silence density found in the data, both in spontaneous and evoked conditions. In the second part of the talk I will show that  UP and DOWN durations are highly variable and that population rates show no significant decay during UP periods. To explain these features of the data, I will present a network rate model with excitatory (E) and inhibitory (I) populations exhibiting a novel bistable regime between a quiescent and an inhibition-stabilized state of arbitrarily low rate. External fluctuations trigger state transitions, while adaptation in E cells paradoxically causes a marginal decay of E-rate but a marked decay of I-rate in UP periods.  I will show that this prediction is indeed found in our data. Finally, I will present a spiking network implementation of this bi-stable model that further predicts that DOWN-to-UP transitions must be caused by synchronous high-amplitude events. These findings provide evidence of bistable cortical networks that exhibit non-rhythmic state transitions when the brain is at rest.

Organized by

Henning Sprekeler, Laura Naumann & Loreen Hertäg