Cortical synchrony is reduced in Alzheimer's disease and relates to arousal state.

INTRODUCTION

The brain is a complex dynamical system, influenced by arousal state. Cortical synchrony supports information processing and is disrupted in Alzheimer's disease (AD). Locus coeruleus (LC) integrity and pupillometry index arousal system structure and function.

METHODS

Sixty-four AD and 26 controls underwent resting-state pupillometry-fMRI. Neuromelanin MRI and Addenbrooke's Cognitive Examination were conducted. Mean and standard deviation of blood oxygen level dependent (BOLD) phase coherence yielded synchrony and metastability, respectively. Leading Eigenvector Dynamics Analysis (LEiDA) produced coherence-based states.

RESULTS

AD had reduced global synchrony [b = -0.90, p < 0.001], metastability [b = -0.61, p < 0.01], LEiDA "global coherence state" occupancy [b = -0.06, p < 0.01], and LC integrity [b = -0.37, p = 0.01]. Synchrony [b = 0.19, p = 0.01] and LC integrity [b = 0.17, p < 0.01] related to cognition and one another [b = 0.27, p = 0.01]. Pupil-linked arousal correlated with synchrony and global coherence state maintenance.

DISCUSSION: In health, cortical activity shows widespread but dynamic synchrony across regions to meet changing demands. In AD, arousal dysfunction appears to disrupt these dynamics, impacting cognition.