Frequency-specific effects of low-intensity rTMS can persist for up to 2 weeks post-stimulation: A longitudinal rs-fMRI/MRS study in rats

Brain Stimul. Nov-Dec 2019;12(6):1526-1536. doi: 10.1016/j.brs.2019.06.028. Epub 2019 Jul 3.

Abstract

Background: Evidence suggests that repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique, alters resting brain activity. Despite anecdotal evidence that rTMS effects wear off, there are no reports of longitudinal studies, even in humans, mapping the therapeutic duration of rTMS effects.

Objective: Here, we investigated the longitudinal effects of repeated low-intensity rTMS (LI-rTMS) on healthy rodent resting-state networks (RSNs) using resting-state functional MRI (rs-fMRI) and on sensorimotor cortical neurometabolite levels using proton magnetic resonance spectroscopy (MRS).

Methods: Sprague-Dawley rats received 10 min LI-rTMS daily for 15 days (10 Hz or 1 Hz stimulation, n = 9 per group). MRI data were acquired at baseline, after seven days and after 14 days of daily stimulation and at two more timepoints up to three weeks post-cessation of daily stimulation.

Results: 10 Hz stimulation increased RSN connectivity and GABA, glutamine, and glutamate levels. 1 Hz stimulation had opposite but subtler effects, resulting in decreased RSN connectivity and glutamine levels. The induced changes decreased to baseline levels within seven days following stimulation cessation in the 10 Hz group but were sustained for at least 14 days in the 1 Hz group.

Conclusion: Overall, our study provides evidence of long-term frequency-specific effects of LI-rTMS. Additionally, the transient connectivity changes following 10 Hz stimulation suggest that current treatment protocols involving this frequency may require ongoing "top-up" stimulation sessions to maintain therapeutic effects.

Keywords: Functional connectivity; Neurometabolites; Resting-state fMRI; Spectroscopy; rTMS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Magnetic Resonance Imaging / methods*
  • Magnetic Resonance Imaging / trends
  • Magnetic Resonance Spectroscopy / methods*
  • Male
  • Rats
  • Rats, Sprague-Dawley
  • Rest / physiology
  • Sensorimotor Cortex / diagnostic imaging*
  • Sensorimotor Cortex / metabolism*
  • Time Factors
  • Transcranial Magnetic Stimulation / methods*
  • Transcranial Magnetic Stimulation / trends