Brain Dynamics During Delirium: An Exploratory Study.

Abstract

Objective: Disrupted Brain dynamics are implicated in delirium. We aimed to better understand the characteristics of functional brain activity as a model for delirium.

Methods: Measurement of functional brain connectivity at rest and during task-based activities in acutely delirious patients in a convenience sample of patients with delirium versus controls. Dynamic jumps between discrete brain states were modelled using the hidden Markov modelling (HMM), an analytical framework that posits the existence of distinct states. Fractional occupancy (FO); the percentage (%) of time any state was active, lifetime; the average time in a given state and switchrate; number of switches per minute, were calculated during rest and task.

Results: Eleven patients were recruited, six had delirium. In the delirious group, 3 were female and the average age was 81 years. In the non-delirious group, 3 were female and the average age was 82 years. Fractional occupancy was no different between delirious and controls across the 10 canonical states (range p=0.09-0.89). Lifetime state dwell time was no different between delirium and controls (range of p=0.11-0.96). The switchrate between all states was no different between delirious cases and controls at rest (6.76 vs. 6.71; p=0.1) and during task (7.26 vs. 7.92; p=0.71). Delirium severity and switchrate correlation was r=-0.29; p=0.39.

Conclusion: A functional MRI paradigm including incorporation of novel task state has shown proof of principle in delirium. Whilst there has been previously shown to be hierarchical dissolution during delirium, there was no difference in functional brain activity shown in this study. The study was approved by the Metro North Reviewing Ethics Committee [Ref No: HREC/17/QRBW/622].