The appearance of a novel or attractive stimulus induces saccadic eye movements and head movements towards the stimulus (orienting response). The mammalian superior colliculus (SC) has been shown to be an important structure for generation of the orienting response. This paper reviews the function of the SC in relation to saccade in the monkey and the cat. Functionally, the SC can be divided into dorsal (superficial) and ventral (intermediate and deep) layers. The former serves primarily as a visual structure receiving input directly from the retina and the striate cortex. Neurons in this layer respond to visual stimuli in the contralateral visual field. These visually responsive neurons are arranged topographically forming a retinotopic map over the SC's surface. The latter receives convergent inputs of multi-sensory modalities (auditory, somatosensory and visual). The auditory, somatosensory and visual receptive fields are arranged in a topographic fasion within the intermediate and deep layers corresponding well to the retinotopic map of the superficial layer. It also receives inputs from the motor-relating areas such as frontal and parietal association cortices and basal ganglia. Electrical stimulation in a given point of the intermediate layer evokes a saccade with a given direction and amplitude. A map of the direction and amplitude can be developed. This motor map is aligned with the retinotopic map. Neurons discharge in relation to the saccade directed to the motor field. It has been suggested that these neurons send descending axons to the contralateral reticular formation including the saccade-generation center. Recent studies reveal that another class of neurons, fixation neurons, are located in the intermediate layer of the rostral SC. These show sustained activities during active fixation and pause during saccade. It is suggested that saccade-related and the fixation neurons have connected mutually inhibitory roles : when the former fires the latter pauses and vice versa. Thus, both the visual and motor maps for the saccade are represented within the SC, suggesting that the SC serves as an important center for sensorimotor transformation for the saccade.
Extraocular motoneurons receive excitatory or inhibitory signals from saccade-related burst neurons in the brain stem during saccades. These premotor neurons are driven mainly by the superior collliculus in the midbrain. Neural models of the saccade system that include the superior colliculus are reviewed with regard to whether the superior colliculus is included in a local feedback loop of the saccade system and how a spatially encoded signal in the superior colliculus is transformed into a temporally encoded signal in the motoneurons.
The prevalence of definitively diagnosed cases of Meniere's disease (M.D.) in eastern Toyama prefecture and the Hida district of Gifu prefecture were examined. Questionnaires were sent to all ENT clinic (general practitioners) and hospitals in both areas. Prevalence was estimated as 18.3 per 100, 000 in eastern Toyama prefecture and 36.6 in the Hida. Prevalence in Hida was higher than that reported in Japan over all. There is a tendency for patients with M.D. to go to an ENT clinic not a general hospital, because M.D. does not cause death. The reasons for the high rate were suspected to be because Hida district is a relatively isolated area of medical care, and the response rate was 100%, and because we surveyed both ENT clinics and general hospitals. Few definitively diagnosed cases of M.D. were reported except in ENT departments. The results showed that a good method of evaluating the prevalence of definitively diagnosed cases of M.D. was to survey ENT departments only.
Acute unilateral loss of vestibular function (UVL) may cause ocular cyclotorsion, skew deviation, head tilt and leaning of the trunk toward the lesioned side. This response (in part) may result from asymmetry of the vestibulo-ocular and vestibulo-spinal reflexes but could be thought of as a realignment of the body with a tilted perception of the subjective postural vertical (SPV) due to vestibular asymmetry. Subjective perception of static uprightness is normal in UVL, probably because proprioception can readily be used for tilt estimation. Accordingly, we examined SPV when proprioceptive cues were changing rapidly. Subjects were challenged to fly a simulator earth level against discrete imposed roll tilts of 10°-28°. They flew in calm conditions and when perturbed by roll oscillations at 1 Hz, 5° peak simulating turbulence. Normal subjects achieved a mean level flight attitude of 0.5° right SD 0.7° when calm and 0.6° right SD 1.3° when turbulent. Patients with unilateral vestibular nerve section flew tilted slightly to the side of their lesion, mean 2.6° SD 2.1° when calm, p < 0.05, and during turbulence by a mean 7.4° SD 2.6°, p < 0.01. We conclude that vestibular signals are used more to determine SPV when proprioception changes rapidly and that the lateralized tilt observed in UVL patients suggests that a unilateral vestibular lesion, probably of the otolith, causes a bias of the SPV.
During vertigo attacks, some patients complain of a strong self-rotating sensation, while others feel only a vague unsteadiness. Interested in this difference, we studied the mechanism of vertiginous sensations. In the present study, we investigated age-related changes in vertiginous sensation during the caloric test and optokinetic response. The subjects consisted of 44 volunteers (10 males and 34 females), ranging from 17 to 78 (mean 43.9) years of age. None of subjects had a history of spontaneous nystagmus, vestibular dysfunction or central nervous disorders. After obtaining informed consent, a total of 176 caloric stimuli were administered by the alternate bithermal method (30 and 44°C) to the bilateral ears of 44 subjects under ENG monitoring. Induced vertiginous sensations were recorded. OKP test was also performed in all the subjects. We obtained the following results; 1) Older subjects tended to complain of a stronger sensation of vertigo on caloric test. 2) There were no remarkable age-related changes in caloric response. 3) Older subjects showed a smaller maximal slow phase velocity on OKP test. This might be attributable to their stronger sensation of vertigo during the test.
It was known that patency of fissula ante fenestram (FAF) and microfissure near the round window niche area (RWF) may cause perilymphatic fistula. However, not all patients have symptoms of hearing loss or dysequillibrium. The perilymphatic fluid communicates with the cerebrospinal fluid through the cochlear aqueduct, thus perilymphatic fistula may depend on the aqueduct. This study is to clarify the relationship between histological patency of the cochlear aqueduct and clinical symptom in the case of patent FAF or RWF. Nineteen human temporal bones with histologically patent FAF or RWF were used in this study. Eight bones were obtained from patients with symptoms of sudden onset hearing loss, progressive hearing loss or vestibular symptoms such as prolonged mild dysequillibrium and positional vertigo, and 11 bones from patients without any hearing or balance problems. Patency of the cochlear aqueduct was scored as one through four. Score one indicated a patent aqueduct and score four indicated a closed aqueduct. The presence of hearing loss or dysequillibrium during life time was determined from clinical charts. The mean score of symptomatic cases was 2.88 and that of asymptomatic cases was 1.91. The difference between the two groups was significant (p<0.05, Wilcoxon-Mann-Whitney test). This finding suggested that a closed cochlear aqueduct might cause symptoms of perilymphatic fistula in patients with patent FAF or RWF.
The subjective visual vertical (SVV), that is, the visual orientation, was measured in forty normal healthy subjects, ten patients with acute Meniere's disease, eleven with Meniere's disease in remission phase, and five with vestibular neuronitis. The SVV was measured by the Rod and Frame test (RFT), which consists of a rod, which subjects rotate until they assume the bar to be vertical, and a frame, which leans 28 degrees to either the right or left to eliminate visual cues. First, the SVV, which was defined as a magnitude of error considering laterality, was measured in forty subjects and then again in 29 subjects to evaluate the normative response in eight trials. e.g., frame : 28 degrees tilted either to left or to right, rod : 28 degrees tilted either to left or right. The mean absolute value of SVV, which was defined as the magnitude of average error from true vertical regardless of laterality, was also calculated to determine the normal confidence limit. The SVV in the healthy group was quite small, and did not change on subsequent tests. The mean absolute SVV with no consideration of laterality in the healthy group was 1.2 degrees. While the SVV in the group with acute Meniere's disease was 5.9 degrees, 3.1 degrees in those in the remission phase, and 6.3 degrees in patients with vestibular neuronitis. The second parameter was frame dependency, and was defined as the condition in which laterality of SVV was consistent with that of the frame. Three of ten (30%) Meniere's disease patients in the acute stage, and three of eleven (27%) in the remission phase showed frame dependency. In contrast, the healthy group, and the vestibular neuronitis patients did not show frame dependency. From these results, we conclude that RFT is a useful device for measuring subjective visual vertical awareness of spatial orientation, and that visual disorientation is found in patient with vestibular disorders.
In seven normal subjects, smooth pursuit eye movements (SPEM), elicited by sinusoidal spot target oscillation, were measured with various backgrounds : the spot target was presented, (1) in darkness (dark), (2) with a stationary textured background (textured), (3) with a moving textured background which was phase-locked to the spot target oscillation at a background/spot velocity ratio of 0.5, 0.75, 1.0 (coupled), 1.25 and 1.5. Spot target oscillation frequencies ranging from 0.2 to 1.6 Hz and peak velocities ranging from 19 to 150 deg/s were employed. Eye movements were measured by a video-based image analyzer (ISCAN system). From the results, compared with the “dark” condition, SPEM gain increased on the “coupled” condition and decreased on the “textured” condition. The influence of background on SPEM gain was significant at higher frequencies and higher peak velocity oscillations, in which the subject failed to continuously keep the target on the fovea because of the low SPEM gain. However, SPEM phase delay were similar for “dark”, “textured” and “coupled” conditions. Since the responses during “coupled” and “textured” conditions are most likely elicited by rapid-rise optokinetic reflex (OKR) interaction, we conclude that the SPEM system is similar to the rapid-rise OKR system. When a phase-locked textured background was presented, “the velocity ratio of 1.0 (coupled)” condition was most prominent in the SPEM gain, i.e. “the velocity ratio of 1.25 and 1.5” conditions never exceeded the “coupled” condition despite the faster background movement. This indicates that optokinetic stimulus (OKS) in the peripheral visual field may be neglected as a driving source of eye movement response when the OKS velocity differed from spot target velocity and only OKS with a velocity equal to the spot target may register in the peripheral visual field.
Detailed gait analysis was performed in patients with acute peripheral vestibular lesion (N=18) and spinocerebellar degeneration (N=13), using foot switches and electromyography. Parameters used in the present study are the interval from heelstrike to forefoot strike (HA-I), interval from heel lift to forefoot lift (HA-II), stance, swing, double supporting duration (DS), and location of maximal contraction of the gastrocnemius during stance (Gc-max). Coefficient of variation (CV) was calculated from the data obtained during fifteen steps on each foot to assess the steadiness of gait. Also average time of appearance of the first and second peak of the tibialis anterior's activity which could be found between early swing and early stance, were calculated. Normal variation was set at the 2sd level obtained from 14 healthy adults. Incidence of abnormalities was highest (83%) in HA-I, which corresponds to body weight acceptance, in the peripheral lesion group, while swing showed the highest (100%) incidence of abnormality in the SCD group. In addition, the number of abnormal parameters in each case was greater in the SCD group than in the peripheral group. HA-II, which corresponds to body weight thrust, showed the lowest incidence of abnormality in both groups. Somewhat earlier appearance of the first peak of the tibialis anterior was shown in the SCD group. These differences between the two groups might reflect pathophysiological differences in the cause of gait abnormality.
The present paper investigated methods of discriminating stabilograms of healthy subjects from those of patients with labyrinthine and central disorders using a neural network (NN). Stabilometry was performed with eyes open and closed with both feet close together for 60 seconds using a stabilometer. From the stabilograms, area, locus length, deviations of the sway, Romberg ratio, power spectrum, position and velocity vectors, and amplitude probability density distribution were measured. Stabilograms were evaluated using a NN program produced by Anima corporation. Data file for learning was composed of healthy subjects and patients with various labyrinthine and central disorders. Data file for evaluation was composed of patients diagnosed with labyrinthine disorders. As a result of learning, stabilograms of healthy subjects and patients of labyrinthine and central disorders were clearly discriminated. The square error was 0.005. In evaluations using a NN weighted by learnig, the square error was 0.326. In medical examinations of patients with vertigo and equilibrium disturbances, discrimination of stabilograms is important for diagnosis of sites of lesion and classification of types and stages of disease. Learning and evaluation using a neural network are expected as a useful method for discriminating stabilograms. However, errors in evaluation (i.e. generalization error) remain high value. In the future, reducing generalization errors is a key issue.