# Cognitive adaptations for memory deficits in MCI and AD patients: A meta-analysis of EEG microstates

## TL;DR

This study uses EEG microstate analysis to identify brain network disruptions in patients with mild cognitive impairment and Alzheimer's disease, suggesting compensatory cognitive strategies.

## Contribution

A meta-analysis of EEG microstate changes in MCI and AD patients reveals distinct patterns of cognitive network disruption and compensation.

## Key findings

- AD patients show increased microstate A and B durations, and reduced microstate C/D occurrences.
- MCI patients exhibit increased microstate A and reduced microstate D parameters.
- Disrupted default mode network and cognitive control processes are linked to compensatory verbal and visual strategies.

## Abstract

•Meta-analysis of EEG microstates in MCI and AD patients versus healthy controls.•MCI and AD patients show increased microstate A reflecting auditory/language activity.•Decreased microstate D in MCI and reduced microstates C/D in AD patients.•Findings indicate a disrupted default mode network and cognitive control processes.•Patients may compensate for memory deficits by verbalizing and visualizing thoughts.

Meta-analysis of EEG microstates in MCI and AD patients versus healthy controls.

MCI and AD patients show increased microstate A reflecting auditory/language activity.

Decreased microstate D in MCI and reduced microstates C/D in AD patients.

Findings indicate a disrupted default mode network and cognitive control processes.

Patients may compensate for memory deficits by verbalizing and visualizing thoughts.

EEG microstate analysis enables the exploration of the brain’s neuronal network activity associated with distinct mental states and cognitive functions in neurodegenerative conditions, such as Alzheimer’s disease (AD). Some studies indicated that AD and patients with mild cognitive impairments (MCI) show a reduced presence of microstate C, which is related to self-related memory functions and mind-wandering and involves brain areas of the default mode network (DMN). However, other studies reported an increased presence of microstate A, which is associated with auditory/language functions. Here, we aimed to systematically investigate alterations in the four canonical EEG microstates (A, B, C, and D) in MCI and AD patients compared to healthy older adults.

We performed a meta-analysis that compared microstate temporal parameters − mean duration, occurrence rate, and time coverage − among MCI and AD patients and healthy older adults. We included 12 experimental studies that examined resting-state, eyes-closed EEG microstate parameters in 1347 participants (448 MCI patients, 514 AD patients, and 385 healthy controls).

We found that AD patients showed increased duration and time coverage of microstate A and increased duration of microstate B, while the occurrence of microstates C and D was reduced. MCI patients also exhibited increased duration, occurrence, and time coverage of microstate A, while all three parameters of microstate D were reduced compared to healthy controls.

These results suggest that MCI and AD patients suffer from disruption in their cognitive control, memory, and self-referential processes. They may compensate for these deficits by verbalizing and visualizing their inner thoughts to maintain cognitive engagement.