Differential modulation of EEG microstate spatiotemporal dynamics by rTMS and iTBS correlates with clinical improvement in Alzheimer's disease.

BACKGROUND: Transcranial magnetic stimulation (TMS) is an effective therapy for patients with Alzheimer's Disease (AD), potentially modulating aberrant functional connectivity. Electroencephalography (EEG) microstates represent transient large-scale resting networks and have emerged as candidate markers for AD. However, their modulation by repetitive TMS (rTMS) and intermittent theta burst stimulation (iTBS) protocols remains to be elucidated. METHODS: Resting-state EEG was recorded from 28 AD patients at baseline and following the 1st, 7th, and 14th sessions of rTMS or iTBS treatment. Polarity-insensitive modified k-means clustering was used to segment EEGs into constituent microstates, which were then subjected to source localization to identify their corresponding cortical regions. Longitudinal changes within subjects in clinical status and microstate parameters (duration, occurrence, coverage, transition probability) were evaluated with one-way repeated-measures analysis of variance, and differences between rTMS and iTBS groups were assessed using t-tests. RESULTS: Four microstates (MS A-D) were identified from EEG data. rTMS predominantly induced sustained suppression of MS-B, whereas iTBS elicited early-phase increases in MS-C activity. Clinical symptoms improvement following TMS correlated with increased MS-C and decreased MS-B activity. Source localization revealed rTMS predominantly modulated MS-B generators in the occipital cortex (impacting visual and dorsal attention networks), while iTBS preferentially engaged MS-C generators in the parietal cortex (affecting sensorimotor and frontoparietal networks). CONCLUSIONS: We identified distinct EEG microstates and their underlying cortical generators associated with clinical improvement in AD following treatment with rTMS and iTBS protocols. The results demonstrate protocol-specific spatiotemporal modulation profiles and temporal dynamics, highlighting differential neural mechanisms of rTMS and iTBS.