Self-organized bistability and its possible relevance for brain dynamics

TL;DR

This paper compares self-organized bistability (SOB) with cortical dynamics theories, analyzing their similarities and differences, and explores SOB's potential role in explaining scale-invariant neuronal avalanches and cortical oscillations.

Contribution

It provides a detailed analytical and computational comparison of SOB and cortical dynamics models, highlighting key differences and the conditions under which SOB may be relevant.

Findings

In the limit of infinitely slow synaptic dynamics, SOB and cortical models become identical.

Biologically plausible timescales for SOB self-organization are unlikely.

Introduces the concept of self-organized collective oscillations in cortical activity.

Abstract

Self-organized bistability (SOB) is the counterpart of 'self-organized criticality' (SOC), for systems tuning themselves to the edge of bistability of a discontinuous phase transition, rather than to the critical point of a continuous one. The equations defining the mathematical theory of SOB turn out to bear strong resemblance to a (Landau-Ginzburg) theory recently proposed to analyze the dynamics of the cerebral cortex. This theory describes the neuronal activity of coupled mesoscopic patches of cortex, homeostatically regulated by short-term synaptic plasticity. The theory for cortex dynamics entails, however, some significant differences with respect to SOB, including the lack of a (bulk) conservation law, the absence of a perfect separation of timescales and, the fact that in the former, but not in the second, there is a parameter that controls the overall system state (in blatant contrast with the very idea of self-organization). Here, we scrutinize --by employing a combination of analytical and computational tools-- the analogies and differences between both theories and explore whether in some limit SOB can play an important role to explain the emergence of scale-invariant neuronal avalanches observed empirically in the cortex. We conclude that, actually, in the limit of infinitely slow synaptic-dynamics, the two theories become identical, but the timescales required for the self-organization mechanism to be effective do not seem to be biologically plausible. We discuss the key differences between self-organization mechanisms with/without conservation and with/without infinitely separated timescales. In particular, we introduce the concept of 'self-organized collective oscillations' and scrutinize the implications of our findings in neuroscience, shedding new light into the problems of scale invariance and oscillations in cortical dynamics.