Normal aging impacts the extent and diversity of neural plasticity induced in the mouse brain with repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation (rTMS) is an attractive tool to promote healthy brain ageing in older adults and treat age-related neurological conditions. Despite its popularity, the neurological processes and plasticity mechanisms altered by rTMS in the aged brain, and where these changes occur in the brain are unknown. Furthermore, it is not known why different rTMS protocols induce different changes in the aged brain, or why rTMS is less effective in older adults compared to younger adults. Using spatial transcriptomics, we uncovered that rTMS primarily acts on genes related to synaptic plasticity in both cortical and subcortical circuits in aged mice, but the specific changes were dependent on the brain region and even down to individual cortical layers in the motor and somatosensory cortices. Comparing our results from aged mice to young adult mice revealed that rTMS acts on a larger variety of neural plasticity mechanisms in the young adult brain, and that rTMS was less effective at altering gene expression related to neural plasticity in the aged brain, but this varied between brain regions and the protocol of rTMS applied. These findings provide a comprehensive map of the mechanisms altered by rTMS across the aged brain and highlight the need to consider the effect of ageing when optimising rTMS protocols for older populations.