Reflecting on mirror mechanisms: motor resonance effects during action observation only present with low-intensity transcranial magnetic stimulation

Michela Loporto, Paul S. Holmes, David J. Wright, Craig J. McAllister

Research output: Contribution to journalArticle

Abstract

Transcranial magnetic stimulation (TMS) studies indicate that the observation of other people's actions influences the excitability of the observer's motor system. Motor evoked potential (MEP) amplitudes typically increase in muscles which would be active during the execution of the observed action. This 'motor resonance' effect is thought to result from activity in mirror neuron regions, which enhance the excitability of the primary motor cortex (M1) via cortico-cortical pathways. The importance of TMS intensity has not yet been recognised in this area of research. Low-intensity TMS predominately activates corticospinal neurons indirectly, whereas high-intensity TMS can directly activate corticospinal axons. This indicates that motor resonance effects should be more prominent when using low-intensity TMS. A related issue is that TMS is typically applied over a single optimal scalp position (OSP) to simultaneously elicit MEPs from several muscles. Whether this confounds results, due to differences in the manner that TMS activates spatially separate cortical representations, has not yet been explored. In the current study, MEP amplitudes, resulting from single-pulse TMS applied over M1, were recorded from the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles during the observation of simple finger abductions. We tested if the TMS intensity (110% vs. 130% resting motor threshold) or stimulating position (FDI-OSP vs. ADM-OSP) influenced the magnitude of the motor resonance effects. Results showed that the MEP facilitation recorded in the FDI muscle during the observation of index-finger abductions was only detected using low-intensity TMS. In contrast, changes in the OSP had a negligible effect on the presence of motor resonance effects in either the FDI or ADM muscles. These findings support the hypothesis that MN activity enhances M1 excitability via cortico-cortical pathways and highlight a methodological framework by which the neural underpinnings of action observation can be further explored. © 2013 Loporto et al.

Original languageEnglish
Article numbere64911
Number of pages7
JournalPLoS ONE
Volume8
Issue number5
DOIs
Publication statusPublished - 28 May 2013

Fingerprint

Transcranial Magnetic Stimulation
Mirrors
Observation
evoked potentials
muscles
Muscle
Scalp
Motor Evoked Potentials
Bioelectric potentials
Muscles
neurons
Fingers
Neurons
axons
Mirror Neurons
Supine Position
Motor Cortex
Axons

Bibliographical note

© 2013 Loporto et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Cite this

Loporto, Michela ; Holmes, Paul S. ; Wright, David J. ; McAllister, Craig J. / Reflecting on mirror mechanisms : motor resonance effects during action observation only present with low-intensity transcranial magnetic stimulation. In: PLoS ONE. 2013 ; Vol. 8, No. 5.
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Reflecting on mirror mechanisms : motor resonance effects during action observation only present with low-intensity transcranial magnetic stimulation. / Loporto, Michela; Holmes, Paul S.; Wright, David J.; McAllister, Craig J.

In: PLoS ONE, Vol. 8, No. 5, e64911, 28.05.2013.

Research output: Contribution to journalArticle

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