High brain network dynamics mediate audiovisual integration deficits and cognitive impairment in Alzheimer's disease

Background Audiovisual integration deficits are frequent in patients with Alzheimer's disease (AD). In addition, patients with AD have altered functional brain networks, such as those supporting auditory and visual processing. However, the mechanisms driving this association remain unclear. Objective To investigate whether dynamic functional network disruptions underlie audiovisual integration and cognitive deficits in AD. Methods Seventy-nine participants (41 AD, 38 controls) completed audiovisual stimuli tasks. A multilayer modularity algorithm was utilized to assess the resting-state fMRI-based brain dynamics of the primary sensory and higher-order functional networks. Mediation analysis was conducted to test our hypothesis. Results AD patients showed delayed response time and reduced peak benefit of audiovisual integration. Dynamic switching rates of primary sensory and higher-order networks were significantly increased in AD, particularly in the dynamic integration between the default mode network (DMN) and visual network (VN). The peak benefit of audiovisual integration negatively correlated with DMN-VN dynamic integration and positively with Mini-Mental State Examination, Montreal Cognitive Assessment, and Auditory Verbal Learning Test delayed scores. Notably, excessive integration between the DMN and VN mediated the relationship between audiovisual integration deficits and cognitive impairment in patients with AD. Conclusions These findings suggest that audiovisual integration impairment may disturb the dynamic integration between the DMN and VN, contributing to cognitive impairment in AD. The neural mechanisms underlying audiovisual integration deficit and cognitive decline might help with early diagnosis and intervention for AD.