Tomohiko Hasegawa

Role of the nucleus of the optic tract in monkeys in relation to optokinetic nystagmus

Nine monkeys were used in order to clarify the role of the nucleus of the optic tract (NOT) in the generation of optokinetic nystagmus (OKN). In 3 monkeys whose NOTs were almost totally damaged, optokinetic stimulus toward the lesioned side failed to generate either eye deviation or OKN and revealed only voluntary saccades, whereas that toward the side contralateral to the lesion generated normal gain of OKN. The phenomenon was identical in either monocular or binocular stimulation. In two of 3 monkeys whose NOTs were partially destroyed, optokinetic stimulus toward the lesioned side produced OKN, but the gain of OKN, but the gain of OKN was at maximum less than 60% in both binocular and monocular stimulation. In the remaining one monkey whose NOT was injured, but superficially, OKN showed normal gain in both directions. In 3 other monkeys whose NOTs were spared, this OKN asymmetry was not observed. Pursuit and saccadic eye movements were normal in all NOT-lesioned monkeys. Visually induced eye movements in the vertical axis were likewise normal. The present experiment suggests that the NOT in monkeys may be the first relay station in the horizontal optokinetic path and that in primates as in non-primates both crossed and uncrossed fibers reach motor centers for OKN via the NOT.

Results of Treatment of Laryngeal Cancer

Eighty-one laryngeal cancer patients treated at our clinic during the past ten years were studied clinically. The proportion of patients in their sixties was highest and the number of males was much larger than that of females, at a ratio of 15:1. Laryngeal cancer was classified as glottic, supraglottic, and subglottic in 58, 19, and 4 cases, respectively, and glottic cancer patients accounted for more than half of these. The cumulative 5-year survival rate in all patients was 79.6%, and the rates in glottic and supraglottic cancer patients were 82.2% and 83.3%, respectively. Cumulative 5-year survival rates in patients in Stages I, II, III and IV were 83.7%, 83.9%, 83.3%, and 55.5%, respectively. Recurrence after radiotherapy was controlled by salvage operations satisfactorily in Stages I and II, but the prognosis of recurrent cancer was poor for patients in Stages III and IV. A selective review is given.

The Effect of Uvulonodular Lesions on Horizontal Optokinetic Nystagmus and Optokinetic After-nystagmus in Cats

The effect of uvulonodular lesions on horizontal optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) was investigated in alert cats. A lesion in each of 6 cats was made by suction-ablation under anesthesia. In the 3 cats with only a uvular lesion, both the initial slow phase velocity and the time constant of OKAN were unchanged. In the remaining 3 cats whose lesions included the nodulus as well as the uvula, the time constant of OKAN was markedly prolonged, but the initial slow phase velocity of OKAN was not affected. The postoperative average time constant of OKAN increased from the normal value of 9 s to about 40 s. In contrast, OKN parameters (the steady-state velocity and the rising time constant) were not affected by uvular or uvulonodular lesions. These results strongly suggest that the nodulus is involved in the velocity storage mechanism and might control the discharge characteristics of the velocity storage integrator.

Electronystagmographic assessment of cerebellar lesions.

Remarkable progress has been achieved in the neurophysiological study of the cerebellum. Based on these neurophysiological data, electronystagmographic (ENG) assessment of cerebellar lesions was made to ascertain to what extent cerebellar lesions could be diagnosed. In 13 patients out of 17 whose lesions were mainly localized on one side through CT, cerebellar lesions could be diagnosed by electronystagmographic findings. In the 1 patient with amyotrophic lateral sclerosis of the remaining 4, asymptomatic cerebellar infarction was detected unexpectedly through CT. In the remaining 3 patients, differential diagnosis from brainstem lesions was difficult to evaluate on the basis of ENG findings. In 13 patients showing cerebellar signs and symptoms, pursuit eye movements, optokinetic nystagmus (OKN), and fixation-suppression of caloric nystagmus were impaired on both sides, suggesting large mass effects upon the bilateral brainstem. However, either rebound nystagmus or opposing positioning nystagmus characteristic of cerebellar lesions was detected in 13 patients (81%). The same was true in patients with bilateral cerebellar lesions. ENG test, however, could not detect any patients who showed neither cerebellar signs nor symptoms. Further investigations are needed to supplement the gap between basic and clinical research.

Effect of Uvulonodular Lesions on Optokinetic Nystagmus and Optokinetic After-nystagmus in Cats

To investigate the effect of uvulonodular lesions on horizontal optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN), 6 cats were tested before and after lesions made by ablation under anesthesia. In the 3 cats with only uvular lesion, the initial slow phase velocity and the time constant of OKAN were unchanged. In the remaining three cats whose lesions included not only the uvula but also the nodulus, the time constant of OKAN was markedly prolonged, and the initial OKAN velocity was not affected. The postoperative average time constant of OKAN increased from normal value of 9 s to about 40 s. In contrast, OKN was unchanged in all of the 6 animals. These findings indicate that the nodulus may contribute to the discharge characteristics of the velocity storage integrator.

Comparative Study on Computed Tomography and Neurotological Findings in Spinocerebellar Degeneration

The classification of SCD on the basis of the neurotological findings was with classification based on CT findings in 40 cass of SCD. The areas of pons, cerebellar hemisphere, vermis and posterior fossa on CT films were measured by craniometer, and were compared in order to estimate the degree of atrophy. From these assessments, patients were classified into 3 types as follows; (1) 14 cases of cerebellar type, (2) 9 cases of brain stem type and (3) 17 cases of combined type. The classification of SCD based on the neurotological findings including the findings of gaze test, positioning test, eye tracking test, OKN, and fixation suppression test of caloric nystagmus, was well correlated to the classification based on CT findings. From the results, neurotological examination was demonstrated to make a contribution to the estimation of lesions and types in SCD.

Rebound Positional Nystagmus as a Peripheral Origin

Three cases of rebound positional nystagmus (RPN) are discussed in the present study. In all cases, spontaneous nystagmus was absent in the primary position, but positional nystagmus appeared in the side down position, and then nystagmus in the reversed direction appeared when the patient was returned to the primary position. The characteristics of RPN in the cases we studied were very similar to those of benign positional nystagmus. Tinnitus was accompanied with vertigo in Cases 2 and 3, and the glycerol tests were positive in Cases 1 and 3. There were no other abnormalities of ocular movements, neurological and neuroradiological examinations suggestive of central nervous system disorders indicating that RPN can be ascribed to peripheral lesions. A selective review of the literature is presented.