Lateralization in motor facilitation during action observation: a TMS study (original) (raw)

Abstract

Action observation facilitates corticospinal excitability. This is presumably due to a premotor neural system that is active when we perform actions and when we observe actions performed by others. It has been speculated that this neural system is a precursor of neural systems subserving language. If this theory is true, we may expect hemispheric differences in the motor facilitation produced by action observation, with the language dominant left hemisphere showing stronger facilitation than the right hemisphere. Furthermore, it has been suggested that body parts are recognized via cortical regions controlling sensory and motor processing associated with that body part. If this is true, then corticospinal facilitation during action observation should be modulated by the laterality of the observed body part. The present study addressed these two issues using TMS for each motor cortex separately as participants observed actions being performed by a left hand, a right hand, or a control stimulus on the computer screen. We found no overall difference between the right and left hemisphere for motor-evoked potential (MEP) size during action observation. However, when TMS was applied to the left motor cortex, MEPs were larger while observing right hand actions. Likewise, when TMS was applied to the right motor cortex, MEPs were larger while observing left hand actions. Our data do not suggest left hemisphere superiority in the facilitating effects of action observation on the motor system. However, they do support the notion of a sensory-motor loop according to which sensory stimulus properties (for example, the image of a left hand or a right hand) directly affect motor cortex activity, even when no motor output is required. The pattern of this effect is congruent with the pattern of motor representation in each hemisphere.

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Authors and Affiliations

1. Ahmanson Lovelace Brain Mapping Center, UCLA School of Medicine, 660 Charles E. Young Dr. South, Los Angeles, CA, 9005-7085, USA
   Lisa Aziz-Zadeh, Fumiko Maeda, John Mazziotta & Marco Iacoboni
2. Department of Psychology, University of California, Los Angeles, USA
   Lisa Aziz-Zadeh & Eran Zaidel
3. UCLA Department of Psychiatry and Biobehavioral Sciences, Neuropsychiatric Institute, UCLA School of Medicine, Los Angeles, USA
   Fumiko Maeda & Marco Iacoboni
4. Brain Research Institute, UCLA School of Medicine, Los Angeles, USA
   Marco Iacoboni
5. Department of Neurology, Pharmacology, and Radiological Sciences, UCLA School of Medicine, Los Angeles, USA
   John Mazziotta

Authors

1. Lisa Aziz-Zadeh
2. Fumiko Maeda
3. Eran Zaidel
4. John Mazziotta
5. Marco Iacoboni

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Correspondence toMarco Iacoboni.

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Aziz-Zadeh, L., Maeda, F., Zaidel, E. et al. Lateralization in motor facilitation during action observation: a TMS study.Exp Brain Res 144, 127–131 (2002). https://doi.org/10.1007/s00221-002-1037-5

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• Received: 17 October 2001
• Accepted: 16 January 2002
• Published: 15 March 2002
• Issue date: May 2002
• DOI: https://doi.org/10.1007/s00221-002-1037-5

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