Imaging the brain before, during, and after transcranial magnetic stimulation

doi:10.1016/S0028-3932(98)00096-7

Neuropsychologia

Volume 37, Issue 2, 1 November 1998, Pages 219-224

https://doi.org/10.1016/S0028-3932(98)00096-7 Get rights and content

Abstract

This article provides a brief overview of current trends in combining neuroimaging and transcranial magnetic stimulation (TMS). First, I outline the utility of magnetic-resonance imaging (MRI) and frameless stereotaxy for planning, monitoring and documenting the location of the TMS coil relative to the subjects brain. Second, I describe two novel methods, based on the combination of TMS with positron emission tomography (PET) or with electroencephalography (EEG), for the assessment of connectivity and excitability of the human cerebral cortex. Finally, I point out the utility of PET and MRI for evaluating possible long-term effects of repetitive TMS.

Introduction

In the last two decades, we have witnessed the emergence of two powerful tools for investigating brain mechanisms of behaviour: functional neuroimaging and transcranial magnetic stimulation (TMS), the former capable of measuring and the latter of changing activity in the human brain. Until recently, these two methodological approaches lived somewhat independent lives. In this article, I provide an overview of the potential that lies in combining TMS with brain imaging. Several examples will be used to illustrate that such a combination can be useful in three principal ways: (1) imaging the brain before TMS, to identify and target the site of stimulation, (2) imaging the brain during TMS, to assess cortical connectivity and excitability, and (3) imaging the brain after TMS, to evaluate possible long-term effects of TMS.

Section snippets

Imaging the brain before TMS

In neuropsychology, the classical paradigm is that of studying the effects of brain lesions on behaviour. With TMS, we can apply this paradigm in spatially and temporally restricted fashion to healthy volunteers. The spatial extent of the effective stimulation depends on the coil design. Using a three-layer (scalp, skull, cortex) spherical model of the head, Roth et al. [34]calculated that, in the case of a figure-eight coil, the magnitude of the induced electric field drops to about 75% of the

Imaging the brain during TMS

While stimulating the brain with TMS, we can measure central effects of this stimulation with a variety of methods. Several early studies employed single-photon emission computerized tomography (SPECT) to quantify changes in brain perfusion during TMS 4, 36. More recently, we have combined TMS and positron emission tomography (PET) to study connectivity of the human cerebral cortex [26]. In this and similar studies 6, 27, 28, TMS is applied while changes in regional cerebral blood-flow (rCBF)

Imaging the brain after TMS

Very little is known about the long-term effects of repetitive TMS (rTMS). At the cognitive level, it seems that a single session of suprathreshold rTMS does not interfere with performance on such tasks as story recall, word fluency or naming [21]. A slight facilitation of the finger-tapping rate and/or delayed recall of a story was observed 1–2 h after rTMS session in some subjects under certain stimulation conditions [44]. TMS of the left and right frontal cortex was shown to change

Conclusion

Transcranial magnetic stimulation is a non-invasive tool for manipulating neuronal activity in the human brain. Functional brain imaging provides a variety of ways to measure the effects of such manipulation, while structural imaging produces a spatial frame-of-reference for both. Thus, combination of brain imaging and TMS should further our understanding of brain–behaviour relationships and the potential of rTMS as a therapeutic tool.15, 39

Acknowledgements

Thanks to Drs Gabriel Leonard, Brenda Milner and Chris Thompson for comments on the manuscript. The authors research was supported by the MNI McDonnell-Pew Center in Cognitive Neuroscience, the Medical Research Council of Canada, Cadwell Laboratories Inc. and Siemens.

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Imaging the brain before, during, and after transcranial magnetic stimulation

Abstract

Introduction

Section snippets

Imaging the brain before TMS

Imaging the brain during TMS

Imaging the brain after TMS

Conclusion

Acknowledgements

Cerebello-frontal cortical projections in humans studied with the magnetic coil. EEG Clin Neurophysiol

Temporal aspects of visual search studied by transcranial magnetic stimulation. Neuropsychologia

Comparison of human transcallosal responses evoked by magnetic coil and electrical stimulation. EEG Clin Neurophysiol

Safety aspects of transcranial brain stimulation in man tested by single photon emission-computed tomography. Neurosci Lett

Transcranial magnetic stimulation of extrastriate cortex degrades human motion direction discrimination. Vision Res

Safety of rapid-rate transcranial magnetic stimulation in normal volunteers. EEG Clin Neurophysiol

A theoretical calculation of the electric field induced in the cortex during magnetic stimulation. EEG Clin Neurophysiol

Topographic mapping of trans-cranial magnetic stimulation data on surface rendered MR images of the brain. EEG Clin Neurophysiol

Transcranial magnetic stimulation of the human frontal eye field. J Neurol Sci

MEG-compatible multichannel EEG electrode array. EEG Clin Neurophysiol

Locating the motor cortex on the MRI with transcranial magnetic stimulation and PET. NeuroImage

Use and safety of a new repetitive transcranial magnetic stimulator. EEG Clin Neurophysiol

Imaging human intra-cerebral connectivity by PET during TMS. NeuroReport

Daily repetitive transcranial magnetic stimulation (rTMS) improves mood in depression. NeuroReport

Changes in mood and hormone levels after rapid-rate transcranial magnetic stimulation (rTMS) of the prefrontal cortex. J Neuropsychiat Clin Neurol

Neuronal responses to magnetic stimulation reveal cortical reactivity and connectivity. NeuroReport

Speech localization using repetitive transcranial magnetic stimulation. Neurology