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

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.

Unilateral and bilateral MRI-targeted repetitive transcranial magnetic stimulation for treatment-resistant depression: a randomized controlled study

“…The strengths of this study include a focus on inclusion of participants with difficult to treat depression with stage 2 or higher treatment resistance, 28 use of sham rTMS as a control condition, localization of the DLPFC stimulation site using cortical coregistration techniques, 24 adjustment of stimulation intensity according to coil-to-cortex distance, 26 treatment duration up to 6 weeks and use of remission rates as a primary outcome. Furthermore, the inclusion of participants aged 18-85 years is another strength of the study as it broadens the clinical applicability of findings.…”

“…10 Second, stimulation intensity may have been insufficient to induce an antidepressant response, as most studies used an unadjusted motor threshold. 26 Adjusting the MT for coil-to-cortex distance increases the stimulation intensity and may improve treatment outcomes. 26,27 Third, several studies had a relatively short treatment duration (i.e., 4 wk).…”

“…26 Adjusting the MT for coil-to-cortex distance increases the stimulation intensity and may improve treatment outcomes. 26,27 Third, several studies had a relatively short treatment duration (i.e., 4 wk).…”

Efficacy of Repetitive Transcranial Magnetic Stimulation (rTMS) in the Treatment of Affective Disorders

“…Sources of variability across studies include differences in stimulation parameter settings, concomitant medications, and different characteristics of patient samples. In addition, simple and economical methods for precise and reproducible coil placement are needed, as this factor is likely to be important for effectiveness (Kozel et al, 2000). In much of this work, the magnitude of antidepressant effect, while often statistically significant, has been below the threshold of clinical usefulness (Berman et al, 2000) and has not lived up to expectations raised by encouraging results in animal studies.…”

Mobilization of Medial and Lateral Frontal-Striatal Circuits in Cocaine Users and Controls: An Interleaved TMS/BOLD Functional Connectivity Study

“…Given that the effects of TMS on cortical depolarization are proportional to the distance between the skull and the cortex (Kozel et al, 2000;Stokes et al, 2005), we calculated the distance from the scalp to the cortex on the transverse plane on MPRAGE images of each individual (Mango ver. Figure S1).…”