Abstract
Background
Transcranial evoked potentials (TEPs) measured via electroencephalography (EEG) are widely used to study the cortical responses to transcranial magnetic stimulation (TMS). Immediate transcranial evoked potentials (i-TEPs) have been obscured by pulse and muscular artifacts. Thus, the TEP peaks that are commonly reported have latencies that are too long to be caused by direct excitation of cortical neurons.
Methods
In 25 healthy individuals, we recorded i-TEPs evoked by a single biphasic TMS pulse targeting the primary motor hand area (M1HAND) or parietal or midline control sites. Sampling EEG at 50 kHz enabled us to reduce the duration of the TMS pulse artifact to a few milliseconds, while minor adjustments of the TMS coil tilt or position enabled us to avoid cranial muscular twitches during the experiment.
Results
We observed an early positive EEG deflection starting after approx. 2 ms followed by a series of superimposed peaks with an inter-peak interval of ∼1.1–1.4 ms in multiple electrodes surrounding the stimulated sensorimotor region. This multi-peak i-TEP response was only evoked by TMS of the M1HAND region and was modified by changes in stimulation intensity and current direction.
Discussion
Single-pulse TMS of the M1HAND evokes an immediate local multi-peak response at the cortical site of stimulation. Our results suggest that the observed i-TEP patterns are genuine cortical responses evoked by TMS caused by synchronized excitation of pyramidal neurons in the targeted precentral cortex. This notion needs to be corroborated in future studies, including further investigations into the potential contribution of instrumental or physiological artifacts.
Transcranial evoked potentials (TEPs) measured via electroencephalography (EEG) are widely used to study the cortical responses to transcranial magnetic stimulation (TMS). Immediate transcranial evoked potentials (i-TEPs) have been obscured by pulse and muscular artifacts. Thus, the TEP peaks that are commonly reported have latencies that are too long to be caused by direct excitation of cortical neurons.
Methods
In 25 healthy individuals, we recorded i-TEPs evoked by a single biphasic TMS pulse targeting the primary motor hand area (M1HAND) or parietal or midline control sites. Sampling EEG at 50 kHz enabled us to reduce the duration of the TMS pulse artifact to a few milliseconds, while minor adjustments of the TMS coil tilt or position enabled us to avoid cranial muscular twitches during the experiment.
Results
We observed an early positive EEG deflection starting after approx. 2 ms followed by a series of superimposed peaks with an inter-peak interval of ∼1.1–1.4 ms in multiple electrodes surrounding the stimulated sensorimotor region. This multi-peak i-TEP response was only evoked by TMS of the M1HAND region and was modified by changes in stimulation intensity and current direction.
Discussion
Single-pulse TMS of the M1HAND evokes an immediate local multi-peak response at the cortical site of stimulation. Our results suggest that the observed i-TEP patterns are genuine cortical responses evoked by TMS caused by synchronized excitation of pyramidal neurons in the targeted precentral cortex. This notion needs to be corroborated in future studies, including further investigations into the potential contribution of instrumental or physiological artifacts.
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Brain Stimulation |
| Vol/bind | 17 |
| Udgave nummer | 4 |
| Sider (fra-til) | 802-812 |
| Antal sider | 11 |
| ISSN | 1935-861X |
| DOI | |
| Status | Udgivet - 2024 |
Bibliografisk note
Funding Information:This work was supported by a Grand Solutions grant \u201CPrecision Brain-Circuit Therapy - Precision-BCT\u201D from Innovation Fund Denmark to Hartwig R. Siebner (grant no. 9068-00025B) and a Collaborative Project grant \u201CADAptive and Precise Targeting of cortex-basal ganglia circuits in Parkinson\u00B4s Disease - ADAPT-PD\u201D from The Lundbeck Foundation to Hartwig R. Siebner (grant no. R336-2020-1035). Mikkel M. Beck is funded by a post doc grant from the Capital Region Denmark (Region H). Lasse Christiansen holds a postdoc grant from The Lundbeck Foundation (grant no. R322-2019-2406). Leo Tomasevic holds an \u2018Experiment grant\u2019 from The Lundbeck Foundation (grant no. R346-2020-1822). Axel Thielscher was supported by The Lundbeck Foundation (grant no. R313-2019-622). We would like to thank Sybren Van Hoornsweder (University of Hasselt) for technical assistance in relation to Figure 1 .
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