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The Journal of Neuroscience, September 6, 2006, 26(36):9272-9281; doi:10.1523/JNEUROSCI.3886-05.2006

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Behavioral/Systems/Cognitive
Transcranial Magnetic Stimulation over Sensorimotor Cortex Disrupts Anticipatory Reflex Gain Modulation for Skilled Action

Toshitaka Kimura,¹ Patrick Haggard,² and Hiroaki Gomi¹

¹NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation, Kanagawa 243-0198, Japan, and ²Institute of Cognitive Neuroscience and Department of Psychology, University College London, London WC1N 3AR, United Kingdom

Correspondence should be addressed to Toshitaka Kimura, NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan. Email: t-kimura{at}idea.brl.ntt.co.jp

Skilled interactions with new environments require flexible changes to the transformation from somatosensory signals to motor outputs. Transcortical reflex gains are known to be modulated according to task and environmental dynamics, but the mechanism of this modulation remains unclear. We examined reflex organization in the sensorimotor cortex. Subjects performed point-to-point arm movements into predictable force fields. When a small perturbation was applied just before the arm encountered the force field, reflex responses in the shoulder muscles changed according to the upcoming force field direction, indicating anticipatory reflex gain modulation. However, when a transcranial magnetic stimulation (TMS) was applied before the reflex response to such perturbations so that the silent period caused by TMS overlapped the reflex processing period, this modulation was abolished, while the reflex itself remained. Loss of reflex gain modulation could not be explained by reduced reflex amplitudes nor by peripheral effects of TMS on the muscles themselves. Instead, we suggest that TMS disrupted interneuronal networks in the sensorimotor cortex, which contribute to reflex gain modulation rather than reflex generation. We suggest that these networks normally provide the adaptability of rapid sensorimotor reflex responses by regulating reflex gains according to the current dynamical environment.

Key words: reflex gain modulation; anticipation; dynamical interaction; sensorimotor cortex; transcranial magnetic stimulation; arm movement control

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Received Sept. 13, 2005; revised July 2, 2006; accepted July 24, 2006.

Correspondence should be addressed to Toshitaka Kimura, NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan. Email: t-kimura{at}idea.brl.ntt.co.jp

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