How Coil–Cortex Distance Relates to Age, Motor Threshold, and Antidepressant Response to Repetitive Transcranial Magnetic Stimulation

TLDR

Repetitive transcranial magnetic stimulation (rTMS) delivers a powerful magnetic field via a scalp‑mounted coil that directly stimulates only the outermost cortex and has antidepressant potential. The study aimed to examine how the distance between the rTMS coil and the cortex influences clinical outcomes. MRI scans were collected from 29 depressed adults undergoing rTMS treatment and analyzed to assess coil‑to‑cortex distance effects. Greater motor cortex distance was associated with higher motor thresholds, but distance did not predict antidepressant response; responders were younger, suggesting an age‑distance threshold for efficacy.

Abstract

Repetitive transcranial magnetic stimulation (rTMS) is a tool with antidepressant potential that uses a coil placed on the scalp to produce a powerful magnetic field that directly stimulates only the outermost cortex. MRI scans were obtained in 29 depressed adults involved in an rTMS antidepressant clinical treatment. These scans were analyzed to investigate the effect of distance from coil to cortex on clinical parameters. Longer motor cortex distance, but not prefrontal distance, strongly correlated with increased motor threshold (P<0.01). Clinical antidepressant response did not correlate with either distance. The rTMS antidepressant responders, however, were significantly younger (t=–2.430, P<0.05), and there appears to be a maximum threshold of age and distance to prefrontal cortex for response.