Exploring causality and phase diversity in brain signals

Different measures of directional influence have been employed to infer functional connectivity in the brain. When the connectivity between two regions is such that one of them (the master) strongly influences the other (the slave), a positive phase lag is often expected. The assumption is that the time difference implicit in the relative phase reflects the transmission time of neuronal activity. However, it has been observed that, in monkeys engaged in processing a cognitive task, a dominant directional influence from one area of sensorimotor cortex to another may be accompanied by either a negative or a positive phase relation.
Here we show that EEG data from humans can also exhibit unidirectional causality with diverse phase relations. We also present a model of two brain regions, coupled with a well-defined directional influence, that displays similar features to those observed
in the experimental data. This model is inspired by the theoretical framework of Anticipated Synchronization developed in the field of dynamical systems. Anticipated Synchronization is a form of synchronization that occurs when a unidirectional influence is transmitted from a sender to a receiver, but the receiver leads the sender in time. This counterintuitive synchronization regime can be a stable solution of two dynamical systems coupled in a master–slave configuration when the slave receives a negative delayed self-feedback.