The intrinsic properties of the brain: the resting state

Abstract:

A growing body of neuroimaging research has documented that, in the absence of an explicit task, the brain shows temporally coherent activity. This so-called "resting state" activity or, more explicitly, the default-mode network has been associated with day dreaming, free association, stream of consciousness or inner rehearsal in humans, but similar patterns have also been found under anaesthesia and in monkeys. Spatio-temporal activity patterns in the default-mode network are both complex and consistent, which raises the question whether they are the expression of an interesting cognitive architecture or the consequence of intrinsic network constraints. In numerical simulation we studied the dynamics of a simplified cortical network using 38 noise-driven (Wilson-Cowan) oscillators, which in isolation remain just below their oscillatory threshold. Time delay coupling based on lengths and strengths of primate cortico-cortical pathways leads to the emergence of two sets of 40 Hz oscillators. \chng{The sets showed synchronisation that was anti-correlated at less than 0.1 Hz} across the sets in line with a wide range of recent experimental observations. Systematic variation of conduction velocity, coupling strength and noise level indicate a high sensitivity of emerging synchrony as well as simulated blood flow blood-oxygen-level-dependent (BOLD) on the underlying parameter values. Optimal sensitivity was observed around conduction velocities of 1-2 m/s, with very weak coupling between oscillators. An additional finding was that the optimal noise level had a characteristic scale indicating the presence of stochastic resonance, which allows the network dynamics to respond with high sensitivity to changes in diffuse feedback activity.