左右大脳半球と注意

Attentional capacity in split-brain patients.

　左右大脳半球を連絡する線維束すなわち交連線維束には脳梁，前交連，海馬交連などがある。1940年代から重症てんかんの治療として，これらの交連線維束の切断手術が行なわれてきた。このような手術をうけた患者，いわゆる分離脳患者は「注意」について2つの問題を提起した。1つは分離脳患者では注意障害が生ずるのかという問題である。いいかえれば交連線維束の切断は注意障害を生ずるのかというテーマである。他の1つは，手術によって分離され独立となった左右の大脳半球はいずれか一方の半球が注意機能において他方より優れているか否かという問題である。本稿ではこの2つの問題について言及したいと思う。

The studies of the attentional capacity of split-brain patients were reviewed. Dimond (1976) tested six split-brain patients with a visual vigilance task in which signals were flashed to the left hemifield (right hemisphere) or the right hemifield (left hemisphere). The patients showed a gross deple-tion of attentional capacity after ten minutes performance. The performance of the right hemis-phere was better than that of the left. Dimond (1979) also reported that the split-brain patients showed the same defect both in a tactual vigilance task and in an auditory vigilance task.

Ellenberg & Sperry (1979) tested fine split-brain patients with two tactual vigilance tasks replicating the tactual vigilance task used by Dimond (1979). In the tactual vigilances tasks, a deline in general levels of arousal was evident within ten to twenty minutes. However, contrary to the result of Dimond (1979) neither hemisphere was consistently inferior to the other in performing the tasks. Ellenberg & Sperry (1979) also tested the patients with seven active sorting tasks which require more motor activity than the vigilance tasks. During the active sorting tasks, the patients were able to sustain continuous attention for periods up to an hour. Neither hemisphere was inferior to the other in the tasks.