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BRAIN and NERVE Volume 63, Issue 9 （September 2011）

BRAIN and NERVE 63巻9号（2011年9月発行）

Japanese English

総説

痛みと痒みの脳内認知機構 Mechanisms of Intracerebral Pain and Itch Perception in Humans 柿木隆介 ^1,2 , 望月秀紀 ^1,2 Ryusuke Kakigi ^1,2 , Hideki Mochizuki ^1,2 ¹自然科学研究機構生理学研究所統合生理研究系感覚運動調節研究部門 ²総合研究大学院大学生命科学研究科生理科学専攻 ¹Department of Integrative Physiology,National Institute for Physiological Sciences ²Department of Physiological Sciences,School of Life Sciences,The Graduate University for Advanced Studies キーワード： pain , itch , magnetoencephalography (MEG) , functional magnetic resonance imaging (fMRI) Keyword: pain , itch , magnetoencephalography (MEG) , functional magnetic resonance imaging (fMRI) pp.987-994

発行日 2011年9月1日 Published Date 2011/9/1

DOI https://doi.org/10.11477/mf.1416101005

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はじめに

　ヒト脳内での痛みと痒みの認知機構の研究は，極めて重要なテーマであるにもかかわらず，種々の技術的困難のために遅々として進まなかった。ヒトを対象とする場合，非侵襲的検査を用いなければならないことが最大の理由である。しかし，近年の科学技術の急速な進歩によって，従来から行われてきた脳波に加え，ポジトロン断層撮影（positron emission tomography：PET），機能的磁気共鳴画像（functional magnetic resonance imaging：fMRI）および脳磁図を用いた研究発表が増加してきた。脳磁図は時間分解能が高いため初期反応の時間的情報を得るのに適しており，fMRIは空間分解能が高いため詳細な活動部位の解析に適している^1,2)。本稿では，痛みと痒みに分けて，それらに関連した脳活動について脳磁図とfMRIを用いた筆者らの最近の研究成果を紹介したい。

Abstract

　Electrophysiological studies involving techniques such as magnetoencephalography (MEG) and hemodynamic studies involving techniques such as functional magnetic resonance imaging (fMRI) have recently been intensively used to elucidate the mechanisms underlying pain and itch perception in humans.　The MEG results obtained after A-delta fiber (first pain) and C fiber (second pain) stimulation were similar, except for longer latency in the case of C fibers.　Initially, the primary somatosensory cortex (SI) contralateral to the stimulation is activated, and the secondary somatosensory cortex (SII), insula, amygdala, and anterior cingulate cortex (ACC) in both hemispheres are then activated sequentially.　The fMRI findings obtained after the stimulation of C fibers and those obtained after the stimulation of A-delta fibers both showed activation of the bilateral thalamus, bilateral SII, right (ipsilateral) middle insula, and bilateral Brodmann's area (BA) 24/32, with most of the activity being detected in the posterior region of the ACC.　However, the magnitude of activity in the anterior insula on both sides and in BA 32/8/6, including the ACC and pre-supplementary motor area (pre-SMA), after the stimulation of C nociceptors was significantly stronger than that after the stimulation of A-delta nociceptors.

　We have recently developed a new stimulation electrode that causes an itching sensation via electrical stimulation applied to skin.　The conduction velocity (CV) of the signals caused by this stimulation is approximately 1 m/sec in a range of CV of C fibers.　The findings obtained after itch stimulation were similar to those obtained after pain stimulation,but the precuneus may be an itch-selective brain region.　This unique finding was confirmed by both MEG and fMRI studies.