How does functional connectivity relate to induced TMS effects on brain activity?

In past years, several studies have found better depression treatment outcomes to repetitive transcranial magnetic stimulation (rTMS) to be associated with high functional connectivity to the subgenual anterior cingulate cortex (sgACC). New targeting methods are thus emerging relying on resting state fMRI to a priori pick optimal stimulation sites. However, the relationship between functional connectivity at the site of stimulation and TMS induced effects remains poorly understood. This talk will shortly cover the latest studies investigating this question before presenting recent findings obtained from our group with interleaved TMS/fMRI. Using baseline resting state functional connectivity mapping to individualize sites of stimulation, we probed cortical targets in the fMRI scanner with single pulses TMS to capture the induced downstream effect in the sgACC. In a cohort including healthy (N=79) and depressed participants (N=32), we found a significant association between the functional connectivity amplitude of our targets and the sgACC evoked response. Sites of stimulation with higher functional connectivity to the sgACC were associated with stronger TMS induced percent signal change in this subcortical region. These findings suggest that the use of functional connectivity targeting and single pulse TMS probing may be a relevant method to optimize TMS stimulation of a given subcortical target. Keywords: TMS, sgACC, target, interleaved TMS/fMRI