Intra‐hemispheric event‐related brain functional connectivity is resilient in patients with amnestic mild cognitive impairment, but not Alzheimer’s disease dementia: A study of event‐related EEG oscillations

Abstract

AbstractBackgroundAlzheimer’s disease (AD) causes abnormalities in structural and functional brain connectivity in relation to cognitive deficits and disabilities in daily living activities.Electroencephalographic (EEG) techniques revealed the part of those abnormalities based on neurophysiological oscillatory mechanisms underpinning the maintenance of quiet vigilance in AD patients (Babiloni et al.,2020).However, it is poorly known the extent to which the brain functional connectivity based on oscillatory mechanisms may be affected in mild cognitive impairment due to AD (ADMCI) and dementia (ADD) involved in the performance of cognitive tasks.In our previous studies, event‐related (ER) EEG oscillations at delta (<4Hz), theta (4‐7Hz), and alpha (8‐12Hz) frequencies were markedly altered in ADMCI and ADD patients engaged in a classical visual oddball‐paradigm requiring focused attention, short‐term memory, and mental counting (Yener et al.,2009,2014).In the present study, we tested the hypothesis that the brain functional connectivity revealed by the ER‐EEG oscillations may be affected in ADD and ADMCI patients as a function of their clinical status.MethodWe enrolled 67 ADMCI, 44 ADD, and 73 demographically‐matched healthy cognitively‐unimpaired persons.The EEG activity was recorded during a visual oddball paradigm with mental counting. The functional brain connectivity was estimated by computing the imaginary part of coherency (ICoh) from the target‐related EEG activity recorded at electrode pairs. Delta, theta, and alpha frequency bands were considered.ICoh values within the hemispheres were compared among ADD, ADMCI, and control groups by an ANOVA design (p<0.05).ResultAll participants tolerated well the experimental setting after instructions, an adequate support, and a preliminary familiarization with the experimental apparatus.They all performed the cognitive task.Notably, the intra‐hemispheric ER‐ICoh at delta, theta, and alpha bands were reduced in the ADD group as compared to ADMCI and control groups (p<0.05).No statistical differences were observed between ADMCI and control groups (p>0.05).ConclusionThe results of the present study suggest that the neurophysiological oscillatory mechanisms underpinning the intra‐hemispheric functional connectivity are resilient during a cognitive task engaging visual focused attention and short‐term memory as they are still normal in ADMCI patients.These mechanisms become abnormal in ADD patients possibly in relation to the worsening of cognitive functions and the occurrence of disabilities in daily living.