Pre-movement modulation of tibial nerve SEPs caused by a self-initiated dorsiflexion Toshiaki Wasaka a,b, * , Tetsuo Kida a , Hiroki Nakata a,c , Ryusuke Kakigi a,c,d a Department of Integrative Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan b Japan Space Forum, Tokyo, Japan c Department of Physiological Sciences, School of Life Sciences, The Graduate University for Advanced Studies, Hayama, Japan d Research in Institute of Science and Technology for Society (RISTEX), Japan Science and Technology Agency (JST), Tokyo, Japan Accepted 2 June 2006 Abstract Objective: To investigate the centrifugal effect on somatosensory evoked potentials (SEPs), we recorded the pre-movement modulation of SEPs following stimulation of the tibial nerve caused by a self-initiated dorsiflexion. Methods: SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded during self-initiated dorsiflexion of the right ankle every 5–7 s. Based on the onset of Bereitschaftspotential and negative slope, the preparatory period before dorsiflexion was divided into four sub-periods (pre-BP, BP1a, BP1b and BP2 sub-period), and SEPs in each sub-period were averaged. SEPs were also recorded in a stationary condition. Results: P30, N40, P50 and N70 were identified at Cz in all subjects. The amplitude of P30 was significantly smaller in the BP2 sub-period than in the pre-BP sub-period. The N40 amplitude was significantly attenuated in the BP2 sub-period compared with the stationary condition, the pre-BP sub-period, the BP1a sub-period and the BP1b sub-period. Conclusions: These results suggested that the motor-related areas involved in generating negative slope modulated the tibial nerve SEPs preceding a self-initiated contraction of the agonist muscle. Significance: The centrifugal gating effect on SEPs extends to the somatosensory information from the antagonistic body part. Ó 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Primary somatosensory cortex; Antagonist muscle; Gating; Negative slope 1. Introduction Somatosensory evoked potentials (SEPs) and somato- sensory evoked magnetic fields (SEFs) have been used to elucidate the processing of somatosensory information in relation to voluntary movement. Processing of sensory information is modulated during movement. This phenom- enon is termed ‘gating’, and SEPs/SEFs are suppressed preceding and during a voluntary movement (Abbruzzese et al., 1981; Rushton et al., 1981; Cohen and Starr, 1987; Bo ¨cker et al., 1993; Kakigi et al., 1995, 1997; Kristeva- Feige et al., 1996; Staines et al., 1997; Morita et al., 1998; Naka et al., 1998; Tinazzi et al., 1998; Shimazu et al., 1999; Valeriani et al., 2001; Asanuma et al., 2003; Nakata et al., 2003; Wasaka et al., 2003, 2005a,b,c; Kida et al., 2004, 2006). For the execution of a precise movement, the appropriate integration of sensory and motor signals is essential. There- fore, a motor function requires sensory signals from the part of body to be moved. At the spinal level, excitation and reci- procal inhibition of agonist and antagonist muscles is a fun- damental feature of the neural basis of motor control. Voluntary contraction of the agonist muscle causes recipro- cal changes in the reflex excitability of the motoneurons of the antagonist muscle, and a depressive effect of the H reflex of the antagonist muscle was revealed preceding and during the voluntary movement (Tanaka, 1974; Kasai and Komiy- 1388-2457/$32.00 Ó 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2006.06.003 * Corresponding author. Tel.: +81 564 55 7811; fax: +81 564 52 7913. E-mail address: wasaka@nips.ac.jp (T. Wasaka). www.elsevier.com/locate/clinph Clinical Neurophysiology 117 (2006) 2023–2029