title: Inhibition of somatosensory-evoked cortical responses by a weak leading stimulus.
abstract: We previously demonstrated that auditory-evoked cortical responses were suppressed by a weak leading stimulus in a manner similar to the prepulse inhibition (PPI) of startle reflexes. The purpose of the present study was to investigate whether a similar phenomenon was present in the somatosensory system, and also whether this suppression reflected an inhibitory process. We recorded somatosensory-evoked magnetic fields following stimulation of the median nerve and evaluated the extent by which they were suppressed by inserting leading stimuli at an intensity of 2.5-, 1.5-, 1.1-, or 0.9-fold the sensory threshold (ST) in healthy participants (Experiment 1). The results obtained demonstrated that activity in the secondary somatosensory cortex in the hemisphere contralateral to the stimulated side (cSII) was significantly suppressed by a weak leading stimulus with the intensity larger than 1.1-fold ST. This result implied that the somatosensory system had an inhibitory process similar to that of PPI. We then presented two successive leading stimuli before the test stimulus, and compared the extent of suppression between the test stimulus-evoked responses and those obtained with the second prepulse alone and with two prepulses (first and second) (Experiment 2). When two prepulses were preceded, cSII responses to the second prepulse were suppressed by the first prepulse, whereas the ability of the second prepulse to suppress the test stimulus remained unchanged. These results suggested the presence of at least two individual pathways; response-generating and inhibitory pathways.
authors: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan. Electronic address: keinaka@nips.ac.jp.
authors: Kei
authors: K
authors: Nakagawa
authors: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
authors: Koji
authors: K
authors: Inui
authors: Division of Bio-Environmental Adaptation Sciences, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.
authors: Louis
authors: L
authors: Yuge
authors: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
authors: Ryusuke
authors: R
authors: Kakigi
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D065808:Prepulse Inhibition / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*
keywords: Inhibitory process; Magnetoencephalography; Paired-pulse suppression; Somatosensory-evoked magnetic field; Weak leading stimulus