脳卒中患者における聴覚の左右差

Difference of Hearing Ability between the Right and Left Ear in Apoplectic Patients

I．はじめに

　そもそも大脳半球は左右に分かれ，左半球障害で失語症，右半球障害で視覚失認を主とした症状が出現することはよく知られた事実である。

　ところで，2つの耳から左右の大脳半球の皮質聴覚野に達する神経路は，途中で一部交叉している。それぞれの半球は両方の耳から入力を受けるが，1つの耳と反対側の大脳半球との結合の方が，同側半球との結合より強くなっている。そして大脳半球内の聴覚機構に，同側耳と反対側耳からの入力が同時に入ってくると，反対側からの入力が同側からの入力を強く抑制または遮断すると考えられている。

　Auditory test was conducted on 120 patients with damage of the one side of cerebral hemisphere (60 cases with the right sided and the other 60 with theleft sided damage).

　The results were as follows :

　1) On pure tone and speech audiometry, about 75% of patients had no difference of scores between both ears. The hearing ability of the ear opposite to the damaged hemisphere of the other patients was impaired.

　2) In the dichotic listening test, the hearing ability of the ear opposite to the damaged side was markedly impaired. It was found that with the stimulation of digits (words), the route of auditory perception was superior from the right to the left hemisphere. However, the environmental sounds were perceived more accurately by the left ear than the right hemisphere.