It is well known that some types of vertigo and dizziness are caused by impairment of the vertebro-basilar systems (VBS). And, it is thought that decreases or lateral differences in blood flow in the inner ear and/or brainstem can induce an imbalance in the equilibrium function and provoke a change in the vestibular excitability in the brainstem. The vascular architecture and hemodynamics were estimated to solve the mechanism of vertebro-basilar dysfunction with some basic findings in the anatomical, morphological and hemodynamic studies of the vestibular and cochlear nuclei in the brainstem. The results are: (1) Many variations in the VBS in human posterior circulation were seen. The VBS is the only parallel vasculature in the skull. The anterior inferior cerebellar artery (AICA) originates symmetrically from the basilar artery (BA) and the posterior inferior cerebellar artery (PICA) originates from the vertebral artery (VA) in about 60% of the cases. Measurement of VAs showed that the left VA was larger across the inner diameter than the right VA. (2) The human vestibular nucleus (VN) area is supplied by some terminal arteries (the penetrating branches in the brainstem), one of which is the median pontine branch from the BA and the others penetrate the brainstem straight and from parallel arrangements with each other in the brainstem. The VN area has fewer circumferential branches and less development in the collateral circulation than the cochlear nucleus. (3) No age-related changes in blood velocity are seen in the human BA. However, the blood velocity in the VA, which has the parallel arrangement, becomes bigger. The cross section of the VA does not decrease, and the arterial wall shows an outer thickness; arteriosclerotic change is "Kalk-Rohr"-like. Therefore, the area supplied by the VA is easily affected by hemodynamic changes. These findings and experiments simulating the VBS (shown in a latter chapter) suggest that hemodynamics in the human posterior circulation differ from those in the anterior circulation.
The nucleus of the optic tract (NOT) in the pretectum has been considered to be the interface between the retina and premotor nuclei in the pathway conveying signals responsible for horizontal optokinetic nystagmus (OKN). However, what parts of the retina and which kinds of retinal ganglion cells project their fibers into the NOT have not been conclusively determined. We injected horseradish peroxidase conjugated with wheatgerm agglutinin (WGAHRP) into the NOT of rats, cats, and monkeys, and identified the labeled cells in the retina. Labeled retinal ganglion cells were observed bilaterally in each of these animal systems as follows: 1. In rats, labeled retinal ganglion cells were diffusely distributed in the contralateral side, whereas those labeled cells were situated only in the lower temporal crescent in the ipsilateral side. 2. In cats, the highest concentration of labeled cells was found in the area centralis and the region adjacent to it in both retinae. These cells were situated only above the horizontal meridian through the optic disk and the area centralis, and they were situated mainly in the temporal crescent involved in the area of the area centralis on both sides. No labeled cells were observed in nasal region of the area centralis on the ipsilateral side. In rats and cats, most of the labeled cells were judged to be small cells, i.e., W cells. However, X-and Y-like cells were also definitely labeled, suggesting that these cells participate in OKN. In the monkey, few labeled retinal ganglion cells were observed above the temporal area of the foveae on both retinae. These were small P γ cells. According to the pattern of cortical development, the distribution of retinal ganglion cells responsible for OKN may be altered so that those in the ipsilateral side in rats are in the lower temporal crescent but those in the cat are in upper temporal crescent at the level of the horizontal meridian. Furthermore, the distribution pattern was changed, and the retinal ganglion cells concentrated in the area centralis. By the time of the appearance of the fovea in the monkey, there are no retinal ganglion cells in the fovea and few small cells above the temporal area in both retinae. Consequently, the pursuit system by the fovea might prevail.
For decades, the gravitational body sway test (GBST) has been used for analysis of static body equilibrium in terms of postural righting function with eyes open and closed. Despite development of a variety of analytical methods for this, it appeared necessary to evaluate the body equilibrium functions during dynamic postural control since the function and dysfunction of the equilibrium may be better revealed during dynamic body movements. Therefore, we developed a new system which can interpret dynamic postural control in relation to visually guided active movements. In essence, this system which tests the ability to track a computer-controlled moving target on a video screen by the gravitational center of the body simultaneously displayed on the same screen enables us to evaluate dynamic postural control. Our "Body Tracking Test (BTT)" interprets the subject's ability to follow the moving visual target by volitionally shifting the body's center of gravity. Thus, the system works with dynamic gravitational bodily equilibrium cued by a visual moving target in concert with the subject's attention/intention. With this system, we are now beginning to understand postural control in the dynamic sphere, and hence to put together the concepts of static and dynamic equilibrium in relation to motor development, motor skills, sports, disease, and rehabilitation.
This study investigated developmental changes in walking in toddlers. Subjects were 122 healthy children aged 1 to 6 years, and 23 healthy adults aged 19 to 22 years. Each subject walked down a 10-m walk-way three times at a preferred natural pace. Walking velocity, step length and cadence were measured. The best time score was selected as the most representative trial for analyses. Results were as follows: (1) Walking velocity and step length increased markedly from 1 to 4 years, especially from age 3 to 4, did not change from 4 to 6 years, and reached the maximum in adults. Step length by height increased from 1 to 4 years, and did not change after 4 years. Cadence decreased gradually with age, but the trends in changes were not marked. (2) Growth of step length was considered due to both (a) longer legs, and (b) greater angle of leg swing due to coordination of hip, knee, and foot flexion between 1 to 4 years, and was especially attributable to longer legs after the age of 4 years.
The vestibulo-collic system senses the head position and movements three-dimen-sionally in space. In turn, it initiates activity in neck muscles that maintain an adequate head position to stabilize the angle of gaze. Surface electromyography (EMG) of neck muscles were recorded to determine responses of the vestibulo-collic system after acute, transient unilateral vestibular impairment resulted from the lidocaine anesthesia of the inner ear as a therapy for tinnitus. Nineteen patients treated by such therapy underwent recording before/after unilateral anesthesia. EMG recordings were obtained using surface electrodes on the sternocleidomastoid (SCM) and splenius (Sp) muscles in a lateral reclining position with the anesthetized ear upward. There were no remarkable changes in surface EMG activity of neck muscles in 3 normal subjects between supine and lateral positions before anesthesia. After anesthesia, EMG activity in the ipsilateral SCM was significantly increasing for 4-6 hours, while there were no remarkable changes in the contralateral SCM or the Sp on either side. Electrophysiological studies demonstrate that SCM motoneurons receive disynaptic excitatory inputs from contralateral vestibular canals and disynaptic inhibitory inputs from ipsilateral canals through the medial vestibulospinal tract (MVST). Taken together, results from this study suggest that increasing EMG activity of the ipsi-SCM could result from "disinhibition" of the inhibitory pathway from the ipsilateral, transiently suppressed vestibular activity due to inner ear local anesthesia.
Stabilometry was performed in 35 patients with equilibrium disturbance. In stabilometry, locus length per unit area (L/A) was examined together with sway pattern, area, deviation of the center of sway and Romberg's coefficient. Twenty-six patients demonstrated unilateral labyrinth disturbance, 6 cerebellar and brain stem disturbance, and 3 Parkinson's disease. 1) In the acute stage of unilateral labyrinth disturbance, stabilogram indicated right-left sway, large area, deviation of the sway to the affected side, and Romberg's coefficient exceeded the reference intervals. The L/A was decreased. 2) In the chronic stage of unilateral labyrinth disturbance, stabilogram indicated centripetal sway, small area, deviation of sway and Romberg's coefficient was within the reference intervals. The L/A was increased. 3) In a patient with spinocerebellar degeneration (SCD), stabilogram indicated for-ward-backward sway, a small sway, deviation of sway to the right-forward, and Romberg's coefficient was within the reference intervals. The L/A remained nearly normal. 4) In another patient with SCD, stabilogram indicated diffuse sway, large sway, deviation of sway and Romberg's coefficient was within the reference intervals. The L/A was only slightly decreased. 5) In the patient with vertebrobasilar insufficiency, stabilogram indicated diffuse sway, large area, deviation of sway in the forward direction, and Romberg's coefficinet was slightly elevated. The L/A was only slightly decreased. 6) In Parkinson's disease with rigidity and akinesia, stabilogram indicated forwardbackward sway, relatively small area, deviation of sway and Romberg's coefficient was within the reference intervals. The L/A was only slightly increased. 7) In Parkinson's disease with postural disturbances, stabilometry indicated diffuse sway, large area, deviation of sway in the right-forward direction, and Romberg's coefficient was within the reference intervals. The L/A was decreased. The L/A indicated fine control of standing posture by proprioceptive reflexes: And examination of L/A was useful in demonstrating the lesion site of patients with equilibrium disturbances.
Step-ramp stimuli were used to distinguish the effects of aging on smooth pursuit eye movements in young and elderly subjects. In this experiment, step-ramp target motions which include four kinds of onward stimulus (2, 4, 6, 8° steps followed by 10°/s ramp) and three kinds of backward stimulus (2° step combined by 9°/s ramp, 4° step; 17°/s, 6° step; 27°/s), were used to test 26 subjects less than 49 years old and 23 subjects more than 50 years old. Eye movements were recorded by infrared reflection oculography with a sampling time of 250 Hz. Data on eye velocity and acceleration were processed with a personal computer. The latency of the response was determined at the time when mean eye acceleration along the base line intersected the line of 100°/s2. Eye acceleration corresponding to the retinal slip velocity (target velocity-eye velocity) was established in each 20 ms segment after pursuit initiation. The relationship between retinal slip velocity and eye acceleration was evaluated by plotting the regression curve for each stimulus. The latencies of smooth pursuit ranged from 145 to 169 ms, and were independent of stimulus conditions. There was a close correlation between retinal slip velocity and eye acceleration in the onward step-ramp target motion study. The x-coefficient of the regression curve in the younger group (y=211x+ 1671) was greater than that in the older group (y=98x+2045) in the step positions of 8° and 10°/s ramp stimulus. These results indicate that younger subjects could produce faster velocity and greater eye acceleration than elderly subjects. Among factors influencing aging effects, the cerebrum might be important, because visual recognition and eye acceleration involve the parietal lobe.
The logarithms of maximal slow phase velocities (MSPV) of caloric nystagmuses showed normal distribution. Taking advantage of this fact, a presumptive mean value and standard deviation of the MSPV of caloric nystagmus were calculated. As a result, the normal range of total MSPV of caloric responses to 44°C and 30°C stimuli were assumed to be 10-70°/sec for each ear. In 413 patients with various kinds of inner ear disturbances, 21 cases showed bilateral vestibular hypofunction. In 248 cases showing a CP% below 26%, four cases showed unilateral hyper-active caloric responses and only two cases showed bilateral hyperactivity. In 144 cases showing a CP% of 26% or more, 13 cases showed unilateral hyperactive caloric responses. The mechanisms of hyperactivity of caloric responses to inner ear disturbances were surmised to involve overcompensation for unilateral vestibular paresis, emotional hypersensitivity of the patient at caloric test or other reasons. However, further observation of each case is clarify the cause.
We report here a case of a 55-year-old man who showed the jumbling phenomenon due to thiamine deficiency. This patient complained of disturbances in visual fixation during walking after about 10 days fasting. His serum thiamine level was low but other serum vitamin levels were within the normal ranges. Neuro-otological examination showed bilateral canal paresis, saccadic pursuit and disturbance of the optokinetic responses. After prescribing thiamine, his clinical symptoms recovered gradually and caloric responses, eye tracking and optokinetic responses improved simultaneously. We consider that the jumbling phenomenon in this case was caused by not only a loss of bilateral vestibular function but also by brainstem dysfunction.
To evaluate the prevalence of definitively diagnosed cases of Meniere's disease (MD) in the West Kubiki District of Niigata Prefecture in Japan, the diagnostic data files and record-linkage system at Itoigawa General Hospital were screened to identify the local residents who were definitively diagnosed with MD between 1991 and 1994. Reevaluation of the patient's data were established according to diagnostic criteria proposed by Meniere's Disease Research Committee of Japan supported by the Ministry of Health and Welfare. Seventeen definite and 55 suspected cases were re-evaluated among 130 patients. All definitively diagnosed patients were evaluated by the ENT department. The prevalence in 1994 was estimated at 21 per 100000 population.
Sway of the body's center of gravity (BCG) in an upright standing posture were studied during horizontal translation of the support surface using a specially designed stabilometer. The experiments were performed on 5 health subjects and 6 patients with unilateral labyrinthine disturbances. They stood on the support surface with their feet 10 cm apart, and the surface was moved at an amplitude of 10 cm at velocities of 2, 4, 6, 8 and 12cm/s, respectively. Backward, forward, rightward and leftward translation were examined with eyes open and closed. Under each test condition, one or three trials were performed. The superimposed and averaged results were displayed. Backward translation with 5 cm/s caused a forward displacement of the BCG with a latency of 20-30 ms (Responce 1, R1), a backward displacement with a latency of 30-45 ms after the onset of R1 (Responce 2, R2) and forward displacement with a large amplitude and a latency of 135-145 ms after R1 (Responce 3, R3) which indicated maximal displacement 145-255 ms after the onset of R3 (Responce 4, R4) and return to the original position before the onset of translation. Responses caused by forward, rightward and leftward translation were similar to the response of backward translation, except for R2 on right and left translation which provide unclear results. R2 and R3 were considered to be displacement due to spinal stretch reflex and dynamic labyrinthine reflex, respectively. Two patients with an intense decrease in caloric response in the affected labyrinth indicated a decrease in R3 induced by translation to the affected side.
In bilateral inner ear lesions, it is not always easy to estimate which ear is responsible for vertigo. We herein show the effectiveness of electrocochleography (ECoG) in determining which ear is causing vertigo in a patient with bilateral Meniere's disease and a patient with delayed endolymphatic hydrops (DEH). Case 1 was a 44-year-old male with bilateral Meniere's disease since 1985. He complained of progressive hearing loss and his hearing had decreased to a level of approximately 55 dB in the bilateral ears. The glycerol test was positive and the caloric response remained normal in both ears. ECoG revealed an increase of negative summating potential (SP)/action potential (AP) ratio in both ears, however the AP value in the right ear (140 uv) was much higher than that in the left ear (24.2 uv). Endolymphatic shunt surgery was performed on the right ear and vertigo attacks disappeared thereafter. Case 2 was a 37-year-old male with profound hearing loss in his right ear first noticed at the age of 7 years. He did not complain of tinnitus in the right ear and had normal hearing in his left ear. Vertigo attacks without cochlear symptoms had occurred every two months since 1993. Caloric response was normal and the furosemide test was negative in both ears. The ECoG revealed an increase in negative SP/AP ratio (49%) in the left ear, indicating that the left ear was responsible for vertigo attacks.