Functional MRI of the immediate impact of transcranial magnetic stimulation on cortical and subcortical motor circuits

Abstract

Recent studies indicate that the cortical effects of transcranial magnetic stimulation (TMS) may not be localized to the site of stimulation, but spread to other distant areas. Using echo-planar imaging with blood-oxygenation-level-dependent (BOLD) contrast at 3 Tesla, we measured MRI signal changes in cortical and subcortical motor regions during high-frequency (3.125 Hz) repetitive TMS (rTMS) of the left sensorimotor cortex (M1/S1) at intensities above and below the active motor threshold in healthy humans. The supra- and subthreshold nature of the TMS pulses was confirmed by simultaneous electromyographic monitoring of a hand muscle. Suprathreshold rTMS activated a network of primary and secondary cortical motor regions including M1/S1, supplementary motor area, dorsal premotor cortex, cingulate motor area, the putamen and thalamus. Subthreshold rTMS elicited no MRI-detectable activity in the stimulated M1/S1, but otherwise led to a similar activation pattern as obtained for suprathreshold stimulation though at reduced intensity. In addition, we observed activations within the auditory system, including the transverse and superior temporal gyrus, inferior colliculus and medial geniculate nucleus. The present findings support the notion that re-afferent feedback from evoked movements represents the dominant input to the motor system via M1 during suprathreshold stimulation. The BOLD MRI changes in motor areas distant from the site of subthreshold stimulation are likely to originate from altered synaptic transmissions due to induced excitability changes in M1/S1. They reflect the capability of rTMS to target both local and remote brain regions as tightly connected constituents of a cortical and subcortical network.

A novel concurrent TMS‐fMRI method to reveal propagation patterns of prefrontal magnetic brain stimulation

“…The application of concurrent TMS‐fMRI is challenged by numerous technical difficulties, a few of which have already been addressed in other works (Bestmann et al, 2004; Ruff et al, 2008). A technical issue which was not previously described is that we observed short deflections (one sample) in baseline activity in a single slice in the vicinity of the TMS coil in EPI volumes during inspection of the BOLD signal (section “Data analysis”).…”

Imaging human brain networks to improve the clinical efficacy of non-invasive brain stimulation

“…Several studies have investigated the impact of local changes in cortical excitability induced by rTMS on the activity of functionally defined neural networks (Bestmann et al, 2004;Eldaief et al, 2011;Cocchi et al, 2015). For example, by combining restingstate functional neuroimaging and frequency-specific (5Hz vs 20Hz) rTMS over left inferior parietal lobule -a non-hub region (Power et al, 2013) -Eldaif and colleagues…”

New coil positioning method for interleaved transcranial magnetic stimulation (TMS)/functional MRI (fMRI) and its validation in a motor cortex study

“…For example, fMRI can be used to measure the blood oxygenation level-dependent (BOLD) activity induced by TMS to demonstrate the connectivity between the stimulated area and coactivated areas (1,2). Alternatively, in the so-called "virtual lesion approach," TMS disturbs task-related activity in a targeted brain region and fMRI monitors the effect on local and remote BOLD activations (3).…”