側頭葉てんかんと認知機能―新しい認知機能研究への展開

Cognitive Function Related to Temporal Lobe Epilepsy: Advances in Research on New Cognitive Function

はじめに

　てんかん領域における認知機能研究の臨床的役割は大きく，知能，言語，記憶機能はじめさまざまな側面から多角的に検討され，これまでにも幅広い領域において多くの知見が得られている。てんかん患者のさまざまな認知機能を評価することはてんかん診療におけるトータル・マネージメントとしての一翼を担い，さらには，発作症候や脳波，各種画像検査などから推定されたてんかん焦点を支持する根拠としての役割も持つ。また，てんかん外科領域においては，術前のてんかん焦点側の言語，記憶機能や，術後の機能回復の有無を評価する必要があり，術前，術後の詳細な神経心理検査による検討は必須となっている。

　本稿では，側頭葉てんかんの外科治療において最も重要な記憶機能について概観し，さらに現在注目されているてんかん患者のノンバーバルコミュニケーション機能としての社会的認知機能へ展開することにより，てんかん領域における認知機能研究の最近の動向について概要を紹介する。

Abstract

　The importance of neuropsychological examinations in epilepsy care and, especially, in epilepsy surgery is centered on the following roles: they offer a means to confirm the epileptic focus by multi-modal preoperative assessments and they help to assess postoperative functional changes based on preoperative cognitive functions. Furthermore, assessments of the cognitive functions of patients with epilepsy using various tests aid in providing comprehensive medical care. Thus far, research on cognitive functions related to temporal lobe epilepsy has focused on memory, language, and general intelligence. However, the concept of social cognitive function has been recently proposed in the field of neuropsychology. This cognitive function, proposed by Brothers in 1990, is a collective term for functions needed in social life; these include functions required to interpret the expressions, feelings, and intentions of others and to form and maintain smooth human relationships while making decisions necessary for self-survival. These functions mainly involve facial expression recognition and decision-making. Findings of research on neural mechanisms underlying social cognitive functions have emphasized the roles of the cerebral limbic system, such as the amygdalo-hippocampal complexes, and the emotional system in the ventromedial prefrontal area. Studies on social cognitive functions in mesial temporal lobe epilepsy are being pursued currently. Early-onset right mesial temporal lobe epilepsy with hippocampal sclerosis is the key substrate determining a severe deficit in recognizing emotional facial expressions and decision-making. In the future, neuropsychological examinations of social cognition, in addition to those of global intelligence, memory, and verbal function, will contribute to the provision of comprehensive medical care to patients with epilepsy.