健常成人におけるP300の加齢の影響

Effect of Aging on P300 in Normal Subjects

　健常人におけるP300の加齢による変化については，現在までの報告では，ほぼ年齢とともに直線的にP300潜時は延長するとされている。しかし，これら対象者の中には，潜在性脳梗塞患者や脳室周囲高信号画像の高度の者などが含まれ，P300に影響している可能性は否定できない。そこで，今回我々は神経学的に正常でかつMRI（0.15 tesla）にて潜在性脳梗塞を認めず，脳室周囲高信号をほとんど認めない104例（35歳〜81歳，平均年齢58.6歳，男性55名，女性49名）を対象として，P300事象関連電位に対する加齢の影響について検討した。P300測定については，auditory oddball課題を用いた。P300潜時の平均はFzで355.2，Czで355.3, Pzで358.6msecであり，P300潜時と年齢との間にはすべての部位で有意の正相関がみられ，1.74msec／year（Cz）延長した。各年代別でみると60歳代から軽度のP300潜時の延長がみられ，さらに70歳代より著明に延長した。P300潜時で男女差は認められなかった。P300振幅と年齢との間にはPzでは，有意の相関関係が認められた。その他N100, P200成分に関しては，潜時，振幅ともに年齢の影響はみられなかった。

The P300 component of the event-related brainpotential (ERP) is generated when subjects discrimi-nate stimulus events which differ from one another. There are many reports about the effect of age on P300 in clinically normal subjects. However, these subjects may include individuals with silent cerebral infarctions or abnormal periventricular hyperinten-sity (PVH) on MRI. In this study, we completely excluded such subjects using MRI and examined the effect of aging on P300. One hundred four neur-ologically normal subjects (mean age 58.6 years, 55 men, 49 women) who had no lesions or severe PVH on MRI were selected. An oddball stimulus para-digm was employed and ERPs were elicited bypresenting a series of binaural 1000 (82%) and 2000Hz (18%) tones through headphones. Prolon-gation of P300 latency was significantly correlated with advancing age (p ＜0.001) : P300 latency in-creased by approximately 1.7 msec per year of age, with a prominent increase after age 60. But there was no significant difference between males and females in P300 latency. The significant correlation between age and P300 amplitude was observed only at Pz (p ＜0.05) . These results indicate that there is a gradual mental decline with aging in normal subjects without silent cerebral infarctions or PVH.