Cerebellar rTMS ameliorates cognitive impairment in Alzheimer's disease: A randomized trial

BACKGROUND: Developing effective neuromodulatory therapies for Alzheimer's disease (AD) is a critical unmet need. While repetitive transcranial magnetic stimulation (rTMS) shows promise, its optimal targets and mechanisms remain incompletely understood. The cerebellum, a key modulator of large-scale brain network dynamics, represents a novel therapeutic target for addressing the distributed cognitive network dysfunction in AD. OBJECTIVE: This study aimed to evaluate the cognitive efficacy and safety of cerebellar rTMS in AD and to elucidate its potential mechanism of action through the lens of structural network topology. METHODS: In this randomized, double-blind, sham-controlled trial, patients with AD were assigned to receive active or sham rTMS targeting the bilateral cerebellar Crus II region. Cognitive assessments were conducted at baseline, post-treatment (4 weeks), and at a 12-week follow-up. Diffusion tensor imaging (DTI) was employed to analyze changes in whole-brain structural network topology. RESULTS: Compared to the sham group, the active rTMS group demonstrated significantly greater improvement in global and domain-specific cognitive function at 4 weeks, with benefits sustained at the 12-week follow-up. Response rates on the MMSE and MoCA were also significantly higher in the active group. Neuroimaging revealed that active rTMS enhanced global network efficiency, indicated by significant increases in global/local efficiency and clustering coefficient, alongside a decreased characteristic path length, signifying an optimization toward small-world topology. Furthermore, treatment selectively enhanced nodal efficiency within core hubs of the default mode, frontoparietal, and salience networks. Critically, these structural improvements correlated with cognitive gains; increased nodal efficiency in the precuneus and posterior cingulate cortex was associated with improved episodic memory and visuospatial function. CONCLUSION: Cerebellar rTMS is a safe and effective intervention that confers sustained cognitive benefits in AD. Its therapeutic mechanism likely involves the reinforcement of structural connectivity and enhanced integrative capacity within supraordinate cognitive networks, particularly the default mode network, via cerebello-cortical pathways.