Some problems in the spectral analysis of human stabilograms are discussed. Power spectra were computed by the following three methods ; fast Fourier transform (FFT) method, autoregressive (AR) models and maximum entropy method (MEM). Power spectra were obtained from original time series (original waves) or separately from the high-pass filtered component (cut-off frequency 0.15 Hz).
A distribution of the power spectra did not reveal any dominant frequency in original waves. The spectra derived from the high-pass filtered component revealed peaks in the majority of cases. It was essential for analyzing the power spectra to cut the lower frequency band from the original waves.
FFT spectra showed large variance and high oscillation. Therefore, it was difficult to detect the dominant frequency. AR and MEM spectra showed stable and smooth spectral curves. Furthermore, since the influence of past sways were taken into account in AR models and the MEM method, these two methods were superior for the detection of periodicity of body sways.

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It has been established that selective retrosigmoidal neurectomy of the vestibular nerve can be performed to cure severe vertigo in patients with Meniere's disease, to avoid postoperative hearing loss and to shorten operation time. It has been considered that the vestibular and cochlear subdivisions of the eighth nerve can be clearly separated in the posterior cranial fossa in most cases, while the vestibulocochlear cleavage plane is hardly visible to the naked eye.
This study was conducted to clarify this discrepancy. We found no macroscopically visible vestibulocochlear cleavage plane in the eighth cranial nerve in the posterior cranial fossa in 18 specimens taken from cadavers for anatomic dissection. We examined histologically cross sections of the nerves about 5 mm distal to the surface of the brain stem using a new staining method (luxol fast blue-PAS-hematoxylin stain : discriminative staining method) that permits simultaneous observation of the axon, surrounding myelin sheath, connective tissue and glia. After confirming the lack of a cleavage plane between the vestibular and cochlear nerves, we were able to differentiate vestibular and cochlear nerve fibers by the transverse area of their axons, the former appearing larger than the latter. The difference was not statistically singificant between the total cross-sectional area of vestibular nerve and that of cochlear nerve. The cross-sectional area of the cochlear nerve decreased slightly with age, but the vestibular nerve did not change with age.

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The endolymphatic sac has been considered to absorb endolymph. Recent studies have revealed that the endolymphatic sac also has a secretory capacity and is closely involved in the regulation of inner ear fluid volume and pressure.
This study was designed to investigate this regulatory function of the andolymphatic sac in an animal model in which the andolymphatic sac and duct had been obliterated unilaterally. Fifteen guinea pigs were used in this study. Twenty four hours after obliteration of the right endolymphatic sac and duct, glycerol was injected intraperitoneally. The animals were sacrificed under general anesthesia, 15, 30 minutes, 1, 2, 4 and 24 hours after the injection of glycerol. The temporal bones were dissected out and fixed with 10% formalin and decalcified with 0.1 M buffered Na-EDTA for 1 month. The specimens were embedded in Agar 100 resin. The sections were stained with toluidine blue and examined with a light microscope.
One to 2 hours after injection, collapse or folding of Reissner's membrane was observed in the operated cochlea with obliterated endolymphatic sac and duct. No remarkable change of Reissner's membrane was found in the non-operated ear with normal endolymphatic sac and duct. In the lumen of the endolymphatic sac of the non-operated ears, material stained with toluidine blue appeared 15 minutes after the injection of glycerol. The volume of this material increased with time and could still be seen 4 hours after the glycerol injection. Twenty four hours after the glycerol injection, no toluidine blue stained material could be seen.
These findings suggested that the endolymphatic sac has a secretory capacity and plays an important role in the regulation of inner ear fluid volume and pressure.

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Evoked electromyograms (EMGs) of the muscles of the lower limbs were induced by galvanic stimulation of the labyrinth in this study of vestibulo-spinal reflexes.
A subject was asked to stand with his eyes closed and his feet close together on a stabilometer and was stimulated with a galvanic current of 1 mA for 3 s by the bipolar-biaural method. In this study, all examinations were carried out with the cathode on the right ear and the anode on the left ear. Evoked EMGs in the soleus, gastrocnemius, tibialis anterior, biceps femoris, rectus femoris and gluteus maximus muscles were observed with the head facing forward and with the head turned to the right and the left.
With the head facing forward, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles increased on the right side and decreased on the left side. The activities of the rectus femoris muscles decreased on the right side and increased on the left side. The activities of the tibialis anterior muscles increased on the right side and could not be observed on the left side. With the head turned to the right, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles decreased on both sides and the activities of the tibialis anterior and rectus femoris muscles increased on both sides. With the head turned to the left, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles increased on both sides and the activities of the tibialis anterior and rectus femoris muscles decreased on both sides.
The muscles of the dorsal surfaces of the lower limbs, such as the gluteus maximus, biceps femoris, gastrocnemius and soleus muscles, showed synergic action, and the muscles of the front of the lower limbs, such as the rectus femoris and tibialis anterior muscles, acted synergically.
These muscle activities were modulated by the head position in spite of having the same galvanic stimulation. The result indicates that when the stimulation is replaced with stimulation by linear acceleration, body deviation occurs in a counter direction to the linear acceleration at any head position. The compensatory body deviation serves to maintain balance
The modulation of the labyrinthine-evoked EMGs of the lower limbs by the head position indicates that the vestibulo-spinal reflexes are regulated by input from the neck proprioceptors.

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The vestibular function of 148 patients with inner ear disturbance was tested repeatedly by the caloric test, during the course of clinical observations for several years.
1) Patients whose caloric responses in the early stage indicated unilateral weakness and later became normal suffered from repeated attacks of vertigo more frequently than did those whose caloric responses remained unchanged through the whole course of observation.
2) Patients whose first caloric responses showed unilateral weakness and later became normal experienced fluctuating hearing more often than did those whose caloric responses were always normal.
3) The caloric responses showed significant changes during the clinical course in 32% of patients with Meniere's disease.
4) Of the patients whose caloric responses changed during the clinical course 66% had Meniere's disease.
These results lead the authors to the conclusion that performing the caloric test repeatedly is useful not only in the differential diagnosis but also in the prognosis of inner ear disturbances.

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To clarify the role of vestibular and proprioceptive reflexes in the regulation of the upright standing posture, we analysed with feedback models sways of the head and of the body's center of gravity (BCG) and the activity of the nuchal and soleus muscles.
Seven healthy adults were asked to stand upright with eyes closed and feet together on a stabilometer. The forward-backward sways of the head and BCG and the activity of the nuchal and soleus muscles were recorded polygraphically. The head sway and the nuchal muscle activity (head-nuchal muscle system) were analysed with a 2-dimensional feedback model to study vestibulo-spinal postural regulation. The sway of BCG and the soleus muscle activity (BCG-soleus muscle system) were analysed with a 2-dimensional feedback model to study proprio-spinal postural regulation.
1. The determinants of the noise correlation matrix in the head-nuchal muscle system and in the BCG-soleus muscle system were close to 1, indicating good feedback.
2. The order. of the autoregressive process, i. e. the length of the past sway forming the present sway, was greater in the head-nuchal muscle system than in the BCG-soleus muscle system.
3. The power spectrum showed a higher power in the frequency range in the BCG sway than in the head sway. The correlogram showed that the correlation ratio decreased more rapidly to the base line in the BCG sway than in the head sway. These results indicate that regulation of the standing posture by proprioceptive reflexes is more minute than that by labyrinthine reflexes.
4. The impulse responses calculated with the head sway as output and the nuchal muscle activity as input were divergent in 4 subjects. The impulse responses calculated with the head sway as input and the nuchal muscle activity as output were convergent in all 7. On the other hand, the impulse responses calculated with the BCG sway as output and the soleus muscle activity as input and with the BCG sway as input and the soleus muscle activity as output were convergent in all 7. These results suggest that the BCG-soleus muscle system provides greater stability than the head-nuchal muscle system.

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The presence of carbohydrates in the vestibular sensory glycocalyx of the guinea pig was investigated with the lectin staining technique. The glyco-calyces of both sensory and supporting cells contain various sugar components. The glycocalyx of the sensory cells, including ciliary interconnections, contains N-acetyl-glucosamine, galactose and mannose, but N-acetyl-galactosamine was not clearly detected. In contrast, the glycocalyx of the supporting cells contains significantly less N-acetyl-glucosamine. The ciliary interconnection, which has been considered to be a part of the glycocalyx, contains more galactose and mannose than does the surface glycocalyx. Therefore, these sugar components may be closely related to the function of the inner ear glycocalyx, and the functional properties of the glycocalyx may differ between the sensory and the supporitng cells of the vestibular end organs.

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Vestibulospinal reactions in the stepping test with pressure applied to the external auditory canal (-300, -200, -100, 100, 200, 300 mmH₂O) were examined in 20 patients with Meniere's disease refered to our clinic from November, 1988 to August, 1989. The angle of rotation of the body around its vertical axis (AOR), the direction of displacement (DOD), and the distance of displacement (POD) from the original position were measured and compared with the results in 59 normal subjects.
1) Marked deviations in AOR were seen in 10% of the Meniere's disease patients ; the DOD and POD results were within normal limits. The ears showing marked deviations in AOR had normal caloric responses.
2) No meaningful correlations were found between the AOR results and those of electrocochleography and glycerol testing.
3) Statistically significant correlations were found between AOR deviation and both duration of disease and the time since the last attack of vertigo.
4) AOR deviation provides a useful indication that Meniere's disease is in the active stage.

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It is said that hearing recovery in idiopathic sudden sensorineural hearing loss (sudden deabness) is worse in patients with vertigo than in those without vertigo. It is also known that vertigo frequently accompanies profound sudden deafness in which complete hearing recovery is extremely difficult. Therefore, the effect of vertigo on hearing recovery cannot be understood in simplistic terms. We evaluated the outcome of sudden deafness with and without vertigo considering the severity of hearing loss, the shape of the audiogram, the time between the onset of symptoms and the first audiogram, and contralateral hearing ability.
The subjects for this investigation included 936 patients who came to our university hosipital within one week of the onset of hearing loss from 1975 to 1989. Of these 936 patients, 247 (26.4 %) had accompanying vertigo. The shapes of their audiogram were divided into five types : low-tone hearing loss, high-tone hearing loss, profound type, flat type and others ; vertigo occurred in 6.0 %, 45.0 %, 66.7 %, 15.8 % and 17.0 %, respectively. In other words, vertigo occurred frequently in patients with severe hearing loss of high-tone frequencies. Hearing recovery of high-tone frequencies was worse in patients with vertigo than in those without vertigo even when the initial hearing loss was the same. We considered that these results were due to anatomical factors, the cochlear basal turn being more proximal to the vestibular apparatus than the upper turn.

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Gait analysis of patients with vestibular disorders was performed with two foot switches placed on each foot to record foot movents. Gait-related activities of the m. tibilis anterior and m. gastrocnemius of both legs were also recorded by surface electrodes on a telemeter. The patients were asked to walk freely with eyes open then closed for a distance of seven meters several times to obtain sufficient data. The data were stored in a data-recorder followed by computer-aided analysis. The parameters employed for the analysis were : time from heel (H) contact to the first caput ossis metarsalis portion (A) contact (HA-I); time from H off to A off (HA-II); stance phase ; swing phase ; double supports ; location of maximum contraction of m. gastrocnemius during stance phase (Gc-max); and location of two-phased contraction of m. tibialis anterior from the early swing phase to the early stance phase. For a comparative study of the steadiness of gait, coefficients of variation were employed for the former six parameters and the average value of the actual measured time was calculated for the latter two parameters. Normal variations were obtained from 14 healthy adults.
The incidence of abnormalities in HA-I was the highest among the eight parameters. CV values increased in each of the parameters when the eyes were closed during walking. The abnormal values returned to normal in the recovery stage. In general, it appeared that the severer the gait abnormality, the higher the incidence of abnormalities in each parameter.
This system of gait analysis was useful and could substanciate a patient's subjective feeling of dysequilibrium even when the gait looked normal.

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Vestibular dysfunction includes a wide variety of impairments of physical capacity due to vertigo and disequilibrium. The purpose of this study was to analyze the relationship between the course of recovery from vertigo and therapeutic exercises for the vestibular system.
The subjects were ten patients, two with Meniere's disease, seven with benign paroxysmal positional vertigo, and one with delayed endolymphatic hydrops. The vertigo of each patient was classified according to Tokumasu's scale and body sway when seated and standing. Therapeutic exercise was performed combining visual, vestibular, and proprioceptive stimulations administered by a physical therapist.
All patients showed good recovery from vertigo after repeated applications of the therapeutic exercise, and the area of body sway also decreased significantly.
The knowledge obtained in the present study can be applied to the treatment of patients with disequilibrium.

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Vestibular nerves of bull frogs were sectioned unilaterally, and angle of the tilt of the head was measured periodically. The angle returned to O degree in an average of 7.3 weeks. At this stage, the anterior and horizontal semicircular canals and the utricle were removed for observation by SEM. The sensory epithelium showed normal structure, and the sectioned vestibular nerve was well united and regenerated. Discrete action potentials could be elicited from the semicircular canals. These results suggest that postural recovery involved two mechanisms : central compensation and reactivation of the end organ.

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Selective VIII th nerve section was performed in two petients with Meniere's disease and one with tinnitus after labyrinthitis. Cerebello-pontine (CP) cistern was approached after suboccipital trephining. The It VIII th nerve was separated into vestibular and auditory portions, and audiotory evoked potentials were recorded. Then either nerve was severed selectively. After the operation, vertigo attacks ceased in the two Meniere's disease patients. Intensity of tinnitus decreased by more than half in all three patients. The post operative time course was uneventful in all three.

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A 30-year-old male complained of vertigo for 2 weeks after taking minocyclin. He then developed left hemifacial palsy, disturbance of left eye abduction, bilateral MLF symptoms, convergence palsy, skew deviation, loss of taste, right hypoglossal nerve palsy, disturbance of micturition., and upward gaze palsy. He was hospitalized, and his symptoms per sisted for 2 weeks. Vertigo became worse, but audiometric and caloric responses were normal bilaterally.
MRI with T2-weighted images showed a high intensity area in the cerebral white matter, but blood, urine, CSF, and enhanced CT examinations were normal except for slight elevation of CSF protein.
With high-dosage predonisolone, the patient improved gradually and left the hospital 3 months later. The patient has been free of recurrence for about 2 years.
Although it was not clear whether the demyelinating disease was MS or ADEM, MS was suggested by the symptoms and laboratory data.

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The possibility of detecting the unilateral recruitment phenomenon in the vestibular system by the rotation test was examined in an analogy model of cochlear recruitment, in which a response from the affected side is characterized by a raised threshold and the intensity of the response above the thresdold asymptotic to that from the normal side.
According to the analogy model, the difference of intensity between leftward and rightward rotational nystagmus reaches its maximum at the threshold stimulus intensity of the affected side and keeps that maximum or decreases above the threshold, so that only in patients with mild hypofunction in comparison with the stimulus intensity range can the difference decrease monotonously (“converge”) with the stimulus intensity, as previouly reported. On the other hand, directional preponderence keeps constant below the threshold and decreases above the threshold.
Moreover, assuming that the ratio of response to ampullopetal to amullofugal stimulation is 2 : 1, the predicted maximum difference of the nystagmus intensity remains within the normal range of variation when the contribution from spontaneous nystagmus is removed. These results indicate that the unilateral vestibular recruitment phenomenon, when it is similar to cochlear recruitment, is difficult to detect by the rotation test. Directional preponderence usaally comes from unilateral hyperfunction in the acute stage or the compensation process of unilateral hypofunction. These factors are not directly related to vestibular recruitment.

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