The Impact of Posture on the Coupling Between Cerebral Blood Flow and Cortical Activity Evaluated via Mutual Information.

Abstract

We investigated the effect of posture on the link between cerebral circulation and cortical activity without applying cognitive tasks. We computed the zero-lag mutual information (MI) between spontaneous variations of mean cerebral blood velocity (MCBv) and the series of spectral powers computed over electroencephalographic (EEG) channels in traditional frequency bands. Estimation of MI was performed according to a fully linear approach and to a technique able to describe nonlinear components of the relationship as well. Time-shifting surrogate approach was utilized to reject the null hypothesis of uncoupling. Analysis was carried out in 27 healthy young individuals (age: 33±8 yrs; 13 males; 14 females) at rest in supine position (REST) and during active standing (STAND). Percentage of rejection of the null hypothesis of uncoupling peaked to 52% and did not vary across the MI estimates and experimental conditions. STAND did not affect MI regardless of the method utilized to its estimate. Results were consistent across brain areas and EEG frequency bands. In healthy young subjects in the absence of task-related activity, neurovascular coupling (NVC) can be assessed from spontaneous fluctuations of MCBv and EEG spectral powers, posture is not a confounding factor, and nonlinear components negligibly contribute to the information exchange between MCBv and resting-state brain activity. The significant values of MI suggest that NVC can be assessed from spontaneous variability of MCBv and EEG spectral power series and was not affected by orthostatic position.