Katsushi Yamada

Sound lateralization in patients with lesions including the auditory cortex: comparison of interaural time difference (ITD) discrimination and interaural intensity difference (IID) discrimination

We examined sound lateralization using dichotic presentation of noises in 15 patients with left unilateral (12 patients) or bilateral (3 patients) temporal lobe lesions, that included the auditory cortex, and evaluated their abilities to discriminate interaural time and intensity difference (ITD, IID) separately. On the ITD discrimination test, discrimination thresholds in patients with left unilateral lesions were significantly higher than those in normal subjects, but all patients with left unilateral lesions could detect ITD. However, none of 3 patients with bilateral lesions could detect ITD. On the IID discrimination test, all patients with either unilateral or bilateral lesions could detect IID. IID discrimination thresholds in these patients were significantly higher than those in normal subjects. The auditory cortex plays an important role in discriminating both cues, but appears to be necessary for discriminating ITD.

Comparison of Interaural Time and Intensity Difference Discrimination in Patients with Temporal Lobe Lesions

We studied the sound lateralization in 15 patients with left (12 patients) or bilateral (3 patients) temporal lobe cerebrovascular lesions. The lesions included the auditory cortex. Interaural time difference (ITD) and interaural intensity difference (IID) discriminations were separately measured by using a self-recording apparatus. All 12 patients with left temporal lobe lesions could discriminate ITD, and their IID thresholds were significantly higher than those in healthy volunteers. None of the 3 patients with bilateral temporal lobe lesions could discriminate ITD. On the other hand, all patients with either unilateral or bilateral temporal lobe lesions could discriminate IID and their IID thresholds were significantly higher than those in healthy volunteers. The present findings indicate that the auditory cortex plays an important role in discriminating both cues, but that the role may not be essential for IID.

Analysis of Optokinetic Nystagmus in Patients with Localized Lesions of Unilateral Visual Cortices

Optokinetic nystagmus (OKN) asymmetry in 4 patients with localized lesions of the unilateral visual cortices (2 in the right hemisphere and 2 in the left hemisphere), confirmed at autopsy or by CAT scan, was detected by computer analysis. The ENG recordings showed typical asymmetry of OKP: lower amplitude in the contralateral optokinetic pattern (OKP) than on the side with the visual cortex lesion. Analysis of this asymmetry revealed lower amplitude, remarkably impaired slow-phase velocity, and mildly impaired fast-phase velocity, with a slight difference in number of OKN. The findings suggested that asymmetry of OKP in patients with localized lesions of the unilateral visual cortices is primarily caused by the impaired slow-phase velocity of the contralateral OKN because of a slight change in number of OKN.

Computer Analysis of the Optokinetic Pattern Test in Acoustic Tumors, Brain Stem and Cerebellar Lesions: Slow and fast phase velocities of optokinetic nystagmus

Optokinetic pattern (OKP) abnormalities in 36 patients with infratentorial lesions were analyzed by microcomputer (7T18 Nihondenki-Sanei). The parameters used for analysis consisted of slow phase velocity (S-VEL) and fast phase velocity (F-VEL) in optokinetic nystagmus. In 16 patients with acoustic tumors, S-VELs were normal or borderline when the tumors were less than 2 cm in diameter, but when the tumors were more than 2 cm, S-VELs were severely impaired. In 20 patients with brain stem and/or cerebellar lesions, S-VELs were abnormal in all the patients with the exception of 3. F-VEL abnormalities were seen in only 5 patients with brain stem lesions, especially pontine lesions. These findings suggest that S-VEL is a sensitive indicator of infratentorial lesions and F-VEL an important indicator of pontine lesions.

Low-Tone Sensorineural Hearing Loss. Therapeutic Effectiveness and Long-term Recuperation.

We often see patients with low-tone sensorineural hearing loss who complain more of a sense of ear fullness than of hearing loss. The cause has not yet been identified but endolymphatic hydrops seems to be the most probable etiology. We studied the effectiveness of therapy of low-tone sensorineural hearing loss.The disease frequently occurs in women aged 20 to 50. The therapeutic success rate is high (71%) and the average until remission is 5.8 days ; the longest was 22 days. But the rate of recurrence was as high as (40.2%). We gave patients various drugs and performed stellate ganglion block. No significant difference was found among the drugs or between drug therapy and stellate ganglion block.We used transtympanic injection of steroid to treat patients with recurrence or intractable disease. Such therapy (steroid targetting therapy) had some effect.

Vestibular Pathology of Totally Deaf Ears

The temporal bone vestibular pathologies of 23 totally deaf ears (16 patients) were studied. Abnormal findings in the saccule were seen more often than in the other vestibular sensory organs. Abnormal findings in the vestibular ganglion cells were found in 7 ears. There were fewer ears with main damage in the hair cells than with main damage in the nerves.

Slow and Fast Phase Velocities of Optokinetic Nystagmus Induced by the Optokinetic Pattern Test in Infratentorial Lesions

Optokinetic pattern (OKP) abnormalities in 36 patients with infratentorial lesions confirmed by CT or MRI were analyzed by microcomputer. The computer analysis system enabled the OKP data to be changed to digital data consisting of the slow phase velocity (S-VEL) and the fast phase velocity (F-VEL) in optikinetic nystagmus. In 16 patients with acoustic tumors. S-VELs were normal or borderline when the tumors were less than 2 cm in diameter, but when the tumors were more than 2 cm. S-VELs were severely impaired. F-VEL abnormalities were not seen in our study except in one patient. In 20 patients with brain stem and/or cerebellar lesions, S-VELs were abnormal in all the patients with the exception of 3. There was no significant difference in S-VEL between the group with brain stem lesions and that with cerebellar lesions. F-VEL abnormalities were seen in only 4 patients with brain stem lesions, especially pontine lesions. These findings suggest that S-VEL is a sensitive indicator for infratentorial lesions and F-VEL an important indicator for pontine lesions.