Background: Investigating approaches for determining a functionally meaningful dorsolateral prefrontal cortex (DLPFC) stimulation site is imperative for optimising repetitive transcranial magnetic stimulation (rTMS) response rates for treatment-resistant depression. One proposed approach is neuro-cardiacguided rTMS (NCG-TMS) in which high frequency rTMS is applied to the DLPFC to determine the site of greatest heart rate deceleration. This site is thought to index a frontal-vagal autonomic pathway that intersects a key pathway believed to underlie rTMS response. Objective: We aimed to independently replicate previous findings of high-frequency NCG-TMS and extend it to evaluate the use of low-frequency rTMS for NCG-TMS. Methods: Twenty healthy participants (13 female; aged 38.6 ± 13.9) underwent NCG-TMS on frontal, fronto-central (active) and central (control) sites. For high-frequency NCG-TMS, three 5 s trains of 10 Hz were provided at each left hemisphere site. For low-frequency NCG-TMS, 60 s trains of 1 Hz were applied to left and right hemispheres and heart rate and heart rate variability outcome measures were analysed. Results: For high-frequency NCG-TMS, heart rate deceleration was observed at the left frontal compared with the central site. For low-frequency NCG-TMS, accelerated heart rate was found at the right frontal compared with central sites. No other site differences were observed. Conclusion: Opposite patterns of heart rate activity were found for high-and low-frequency NCG-TMS. The high-frequency NCG-TMS data replicate previous findings and support further investigations on the clinical utility of NCG-TMS for optimising rTMS site localisation. Further work assessing the value of lowfrequency NCG-TMS for rTMS site localisation is warranted.

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