心理現象・精神症状の脳機能と近赤外線スペクトロスコピィ（NIRS)

Near-infrared Spectroscopy in Psychiatry

Ⅰ．自然な状態の脳機能と近赤外線スペクトロスコピィ（NIRS）

　1．心理現象・精神症状と自然な状態の脳機能研究の重要性

　心理現象や精神症状は，脳機能により担われている。その解明に用いられる脳機能画像検査法のfMRIなどは大規模な装置で，被検者はガントリーに仰臥位となり検査を受ける。したがって得られる結果には，検査室という特殊な環境，騒音やそれを防ぐ装具の着用，仰臥位という姿勢など，被検者が日常生活とは異なる状況と状態に置かれた影響が含まれると考えられる。

　日常経験から類推すると，そうした影響は視覚や聴覚などの遠感覚や注意や記憶などの認知機能については比較的少なく，体性感覚や味覚などの近感覚や情動や意欲などの情意機能については大きいと予想できる。例えば，情動には闘争／逃走の判断という動物にとっての重要な機能があり，そのため情動と姿勢は密接に関連し相互に影響を与え合う。心理現象や精神症状は情意の機能と関連が深いので，その脳機能を検討する際に自然で日常生活に近い状況と状態で検査ができれば，fMRIなどではとらえにくい結果が得られる可能性がある。動物における社会性の脳機能については，そうした自然な状況での研究の重要性が注目されている¹⁾。

Abstract

　Near-infrared spectroscopy (NIRS) is a functional neuroimaging technique that has been increasingly employed in psychology and psychiatry. Because NIRS can detect only cerebral cortex reactivities with low spatial resolution and may suffer from contaminating signals from the skin and skull,its data should be interpreted as a global index of cerebral cortex reactivities. Within these limitations,the advantages of NIRS over fMRI such as complete non-invasiveness,small measurement apparatus,high time resolution,and natural examination setting,makes it the preferred method in studies of brain substrates of subjective feelings of sleepiness and fatigue,personality,conversation,and psychiatric disorders. Two-thirds of the original articles on NIRS applications in psychiatry have been published by Japanese researchers. NIRS examination of psychiatric disorders using a verbal fluency task of only 3 minutes demonstrated their characteristics of frontal lobe function: depression was characterized by smaller activation,bipolar depression by comparable but delayed activation,and schizophrenia by reduced activation followed by re-activation during the post-task period. These characteristics can also be identified in individual NIRS data using 2 automatically calculated parameters. Based on these results,NIRS application in psychiatry has been approved as one of the Advanced Medical Technologies in 2009 as an aid for differential diagnosis of depressive symptoms. A lack of clinical laboratory tests for diagnosis and treatment has been one of the major difficulties for reliable diagnosis,quantitative treatment assessment,and prevention of psychiatric disorders; NIRS may be the first step toward such clinical laboratory tests in psychiatry.