Brain imaging studies related to spatial orientation were reviewed. Visual perception of motion and space is processed primarily in the dorsal visual pathway, in which the dorsal cuneus, parieto-occipital sulcus area, MT, MST and parietal cortex play essential roles. However, the lingual gyrus and fusiform gyrus in the ventral pathway also play important roles in visuo-spatial perception. In the parietal cortex, the intraparietal sulcus and inferior and superior parietal lobules are activated by various tasks that are related to visual perception of orientation, location and motion in space. In addition to these areas, visuo-spatial attention activates the anterior cingulate gyrus and premotor cortex, and the insula and hippocampus are activated by tasks related to perception and memory of self-motion, and navigation in space. Most of these regions also become active by vestibular and somatosensory stimuli, and contribute to controlling ocular and body movements. Several imaging studies have demonstrated reciprocal inhibitory interactions among visual, vestibular and somatosensory systems. Inhibitory interaction between different sensory perception systems may contribute to developing consistent and unified self-image and appropriate behavior in space when they disagree.
In this paper, we report our development of an analytical index on stabilometry to diagnose a decrease in the cerebellar equilibrium function controlling vestibulo-spinal reflex. We measured the sway of the center-of-gravity of the body with a stabilometer for seven healthy men aged 19 to 26 years, and also recorded statokinesigrams after alcoholic intake. We propose classification of these statokinesigrams under two groups, statokinesigrams before the intake and after it. Suzuki et al. (1996) standardized indices, area of sway, total locus length and other parameters, on stabilometry, however, it was difficult to classify statokinesigrams with those indices. Here, we introduce a new index, sparse density, into stabilometry. We show that sparse density is a useful and stable index for classification in accordance with non-parametric statistics. Although we expected a similar effect on the circulatory system by the alcoholic load, variation of these indices was more complex than the variation derived from the organs for the recovery from the standpoint of time. We also analyzed data by paying attention to the force acting on them, which generated the statokinesigrams. We especially turned our attention to singular points where statistically tiny or huge forces are exerted. We could pursue the sparse density with sum of local force that acted on the center-of-gravity. We concluded that sparse density depends upon the function for the control of the center-of-gravity of the body.
The subjective visual vertical (SVV) is often used to evaluate asymmetry of otolithic function clinically. However, there is no established method of measuring SVV. This study assessed the effects of head location and visual (monocular or binocular) condition on measurements of SVV. The reproducibility of SVV was also examined. The normal subjects with no history of ear diseases participated in this study. When myopic or astigmatic, they were allowed to wear glasses or contact lenses during the measurements. SVV was measured with the seated subject's head loosely fixed in the upright position. A bar was placed 30 cm in front of the subject's face to assess SVV using a joystick. To eliminate clues for verticality, a hemispheric dome 60 cm in diameter and covered with a random pattern of dots covered the entire visual field behind the target. Each session consisted of a total of nine head and visual conditions (three different head locations times three different visual conditions). Ten measurements were carried out for each condition. In all, 90 measurements were carried out in each session. Two measurement sessions were carried out daily, 15 minutes apart, on five consecutive days. Our findings showed that (1) the reproducibility of the results was poor, even under the same head and visual conditions; (2) of all nine conditions used, measurement in the binocular condition while the visual target was precisely in front of the face produced the most reproducible results with the least variance; (3) when the visual target was placed to the right of the subject's field of view, the average SVV tended to shift in a counterclockwise direction from the same perspective; and (4) the average SVV when viewed in the binocular condition was close to that when viewed in the monocular condition using the predominant eye. These results suggest that the gravity vector is not fixed, but is moving constantly, even in normal subjects. They also showed that when possible, it is desirable to measure SVV in the binocular condition, with the target precisely in front of the subject.
Plugging of the right lateral semicircular canal was performed in a patient with intractable positional vertigo. Caloric test using cold water showed weak, but distinct horizontal nystagmus to the left. The direction of the nystagmus was unchanged when the head position was moved 180 degrees along the sagittal plane. MRI of the inner ear showed disappearance of the right lateral canal from the plugging point toward the canal end. Our previous experiment confirmed that thermoconvective effect is eliminated and volume change effect is enhanced after canal plugging. The enhanced effect of volume change after the lateral canal plugging is possibly a mechanism of the caloric response observed in the present case.
The canal repositional procedure (CRP) significantly relieves paroxysmal sym-ptoms of benign paroxysmal positional vertigo (BPPV), and accurate diagnosis of BPPV as well as identification of the site of the debris improves the efficacy of the therapy. However, BPPV is not only cause of positional vertigo, other diseases could also cause positional vertigo. We studied 248 patients admitted to our department at Osaka City University Hospital with the positional vertigo, to determine the frequency of BPPV and other lesions. Of these, 143 (57.7%) had peripheral lesions and 105 (42.3%) had evidence of central lesions. BPPV was found in 87 (35%), 5 of these BPPV cases were associated with central lesions. Physicians must be aware that it may be difficult to distinguish central lesions from BPPV on the symptoms.
We report the case of a young child suffering from vertigo and hearing loss caused by asymptomatic mumps. A three-year-old boy showed loss of body balance and vomiting. There was no swelling of the parotid glands and he did not complain of hearing loss, but we found he had spontaneous nystagmus to the left. During the medical examination, he staggered to the right from the standing position. After ABR testing, we found abnormality of his right ear and the testing showed high indices of mumps IgM and IgG. CT findings suggested tympanitis in his left ear, but no such sign was seen in the right. As a result of these tests we diagnosed asymptomatic mumps causing dizziness and hearing loss. Four months after he became ill, we found his spontaneous nystagmus had disappeared, but after head shaking nystagmus testing, nystagmus to the left was still observed. Subsequently, we observed that the patient often ran in the opposite direction from which his name was called. It is very rare for young children to complain of dizziness and vertigo. We should be aware that some children with hearing loss may not complain of symptoms. Physi-cians must also keep in mind that inner ear disorders can be caused by asymptomatic mumps. The number of mumps infections is on the increase. This disease is very hard to cure, so vaccination against mumps needs to be encouraged.
By the use of a tactile sensor placed under both feet, gait analysis was performed in patients with vestibular system disorders and compared with normal subjects. One group of patients with vestibular neuronitis (VN) and another with spinocerebellar degeneration (SCD) were studied. The variables employed for the present study were stability of foot pressure progression, foot pressure difference between both feet and average length of trajectory of center of force (TCOF). Irregularity of foot pressure progression, especially from body weight acceptance to body weight translation, was found in both groups, however, SCD subjects showed more variation than VN. The irregularities became greater under gait with eyes closed. Greater foot pressure on the lesion side foot was in found more than half of VN patients and even greater with eyes closed. No significant difference was noted among SCD cases. As for the length of TCOF, significantly longer trajectories were found in SCD patients. Such changes could reflect different disease entities in the two groups.
Standing while making an effort to reduce postural sway (corrective standing, C-standing) was compared with natural standing (N-standing) to study the peculiarities of voluntary control in standing posture. Sway of the body center of gravity was recorded with eyes open and closed with both feet close together for 60 seconds using a stabilom-eter. 1) Whilcoxon-test was used to compare the results. In C-standing with eyes open, the area and the ratio of low frequency bands on power spectra and the kurtosis of amplitude histogram on the x-axis (right-left movement) increased and the length/area decreased.2) Patterns of statokinesigrams showed a non-specific type or a right-left enlargement type in C-standing with eyes open.3) Autocorrelograms of body sway showed a loss of periodicity on the x-axis in C-standing with eyes open.4) Attractors reconstructed from time series data obtained from the records showed a convergence of locus in the phase space on the x-axis in C-standing with eyes open. Voluntary correction aimed at reducing the body sway in upright standing converted from rhythmic regular control (negative feedback control) depending on labyrinthine and proprioceptive reflexes to irregular adaptive control (positive feedback control) rely on visual information.
In 1968, the Japan Society of Vestibular Research changed its name to Japan Society of Equilibrium Research (JSER) with the idea that vestibular function should be investigated from the point of view of body equilibrium in relation to visual and proprioceptive function. In the period from 1968-2000, progress in the following studies was noticed: (1) 3-dimensional recording of nystagmus and eye movements, (2) analysis of the body sway in upright standing posture, (3) examination of otolithic organ using vestibular evoked myogenic potential, linear acceleration and eccentric rotation test, (4) diagnosis, epidemiology and conservative and surgical treatment of Meniere disease, (5) diagnosis of vertigo and equilibrium examination using neuro-otological examination, computed tomography and magnetic resonance imaging, (6) training and rehabilitation for equilibrium disturbances, (7) localization and function of vestibular cortex, (8) eccentric rotation testing in the space shuttle. Currently, evidence-based medicine for vertigo, and regeneration of the sensory epithelium of the inner ear are new subjects in vestibular investigation.