When an animal moves its eyes and head to fixate a visual target which has appeared in the periphery of the visual field, its central nervous system has to synthesize the motor command to execute well-coordinated activation of a large number of extraocular and neck muscles based on the visual information as to the target location perceived by the retina. Thus, the visuo-motor transformation process during such behavior involves an ill-posed problem and the process should have some constraints for the brain to solve the problem uniquely. However, neural implementation of the constraint is not well understood. The superior colliculus (SC) is a center for the control of visually-guided orienting movements of the eyes and head, whose output encodes a vector of gaze movement. With regard to the control mechanism of the head movement, the output command from the SC is transmitted to neck motoneurons via two major subgroups of interneurons in the brainstem reticular formation; one group in the medial pontine reticular formation and the other group in Forel's field H in the reticular formation of the mesodiencephalic junction. The former group of interneurons control the horizontal component, and the latter control the vertical component of the head movement. Each of these interneuronal populations represents a “functional synergy” of the neck muscles. Such parceling of head movements into two major subcomponents may serve as a neural constraint to reduce the number of degrees of freedom of the complex and redundant skeletomotor system such as the neck and may help the brain solve the ill-posed problem imposed on the visuo-motor transformation process during gaze movements.
The neural mechanism for coordinate transformation is an important issue for understanding how the brain constructs body-centered motor programs from retinotopically-organized visual inputs. Although visual properties examined in many areas outside the striate cortex have been shown to be arranged retinotopically, some parietal neurons and ventral premotor neurons encode locations of visual stimuli craniotopically. These indicate that retinotopically-organized visual information is transformed craniotopically within the brain. The response magnitude of posterior parietal neurons to visual stimuli presented at identical retinal positions was affected by the monkey's angle of gaze. A computer simulation revealed that the angle-of-gaze effect reflects a neural mechanism related to transformation from retinotopically-coded visual information to head-centered spatial information. This result suggests that the transformation from retinotopic coordinate to head-centered coordinate is achieved in the posterior parietal cortex. However, the angle-of-gaze effect has been observed not only in the parietal cortex but also in the V3A and frontal cortex, suggesting that coordinate transformation could be performed in parallel in different cortical areas.
Abnormal activity of neurons in the brainstem vestibular nuclei is related to the onset of dizziness in hemodynamic vertebrobasilar insufficiency (VBI). In the present study, we compared the vestibular nuclei (VN) with the cochlear nuclei (CN) and the inner ear in terms of the reactions of brainstem and inner ear neurons and investigated the influence of ischemia on the VN in a vertebrobasilar insufficiency model. The following conclusions were obtained : 1. Comparison between the VN and CN 1) When the unilateral VA was occluded, the activity of ipsilateral VN neurons decreased, but the activity of CN neurons showed no change. 2) When the unilateral VA was occluded with hypotension, immunohistochemical staining of the dendrites decreased around the VN only, while staining CN neurons did not change. When the basilar artery was occluded with a trap, VN staining decreased more than that of CN. 3) As a result of unilateral VN occlusion, the ipsilateral caloric nystagmus decreased, but the ABR did not change. When hypotension was added, the former decreased more markedly, while the latency of the latter was prolonged. 2. Reaction of VN in ischemia models 1) The activity of ipsilateral VN neurons was decreased more by the unilateral VA occlusion plus hypotension than by unilateral VA occlusion alone. The severity of disturbance was greater in the presence of VA stenosis than with VA occlusion. 2) Release of glutamic acid in the VN did not change in the presence of the unilateral VA occlusion, but increased when hypotension was added. 3) The glucose utilization response in the VN following stimulation of the ipsilateral inner ear with cold water was inhibited by unilateral VA occlusion combined with hypotension. 3. Comparison between the VN area and the inner ear 1) When the unilateral VA was occluded, the activity of the ipsilateral VN neurons decreased, but the activity of neurons in the vestibular ganglion (VG) showed no change. 2) As a result of VA occlusion combined with hypotension, the caloric nystagmus test showed CP in all cases, but the ABR did not any change in the I wave. 3) In the absence of VA occlusion, control of blood flow was better in the brainstem than in the inner ear. However, in the presence of unilateral VA occlusion, control was more severely disturbed in the brainstem than in the inner ear. 4. The above experimental results showed that the VN is injured more easily than the CN or inner ear in the presence of VA occlusion plus hypotension. We conclude that the susceptibility of the VN to ischemia leads to the onset of dizziness in hemodynamic VBI.
To evaluate the influence of spatial orientation upon stance regulation, we gave Coriolis' stimulation to the subject standing on the turntable, and the findings were compared to those of eye movements. Six healthy adult subjects were asked to wear goggles and stand on a force platform at the center of the turntable with legs together. They performed a forward head tilt (30 deg) while rotating at a constant velocity. Perturbations of body and eye movements were evaluated by shifts in the center of pressure and recordings by a CCD video camera, respectively. Rotation velocity was increased by 15 deg/sec. None of the subjects touched the handrail of the turntable at rotation velocities less than 30 deg/sec. The center of pressure shifted to the left under clockwise rotation, and to the right under counterclockwise rotation. The direction of body perturbation resembled the direction of slow phase in induced nystagmus. The center of pressure shifted in the direction opposite to the physical force given to the head (Coriolis' force), that is, to the direction of transient movement of the spatial framework in the brain. From the present study, it seems likely that spatial orientation plays an important role in regulating stance, and that posture is subjected to a simple rule, as eye movements are.
Several stabilometric studies of the characteristics of labyrinthine equilibrium disturbance have been reported, but it is difficult to directly discriminate the degrees of labyrinthine damage and the stages of labyrinthine equilibrium disturbances (stages of disturbances, coordination and compensation) using stabilometric findings. The present study was designed to discriminate the degrees and stages of disturbance by neural network (NN) evaluation after learnings using measurement values of stabilograms from patients with labyrinthine disturbances. On stabilograms, envelope area, length/time, length/area, deviation on X-and Y-axes, and Romberg's coefficient were measured. Learning and evaluation by NN were performed using a program developed by Anima corporation. As the method of learning, we compiled a data file for learning and designated the composition of net, then practiced. As the method of evaluation, we compiled a data file for evaluation and evaluated the data by a weight file which was acquired in the process of learning. Learning and evaluation by NN were carried out using the following 2 supervised signals : (1) percent of canal paresis (CP%) obtained from caloric test. (2) stage of labyrinthine disturbance diagnosed by clinical findings. Results : (1) For discrimination of the degree of labyrinthine damage stabiometric results were noncontributory. (2) Stabilograms of patients with various stages of disturbances, coordination and compensation were discriminated with a square error of 0.06. The NN was useful for discriminating the stages of labyrinthine disturbances.
The diagnosis of spinocerebellar degeneration has been based on neurological, neuro-otological and radiological findings. CT scan and MRI can demonstrate atrophy of the cerebellum and/or pons on a two-dimensional plane. In this paper, three-dimensional evaluation by volumetry of the cerebellum and brain stem from MRI in 4 patients with spinocerebellar degeneration and 2 normal subjects was reported. MR images of the cerebellum and/or brain stem were put into a personal computer (Macintosh 7600/200), reconstructed three-dimensionally. Volume of the cerebellum or brain stem was calculated using commercial software (Vox Blast, Vay Tec Inc). In normal subjects, measured volume of the cerebellum was around 90 ml and that of the brain stem 17 ml. In patients with spinocerebellar degeneration, 2 patients with the cerebellar type showed reduced volume of the cerebellum with normal volume of the brain stem, while 2 other patients with the spinocerebellar type showed reduced volume in both the cerebellum and the brain stem. The authors considered that three-dimensional volumetry of the cerebellum and brain stem is useful for diagnosing spinocerebellar degeneration.
The therapeutic effects of bromazepam, a minor benzodiazepine tranquilizer, were evaluated in 32 patients with vertigo or dizziness. The patients were given 2 mg of bromazepam once a day for over 4 weeks. In 21 patients (65.6%), symptons and/or signs were reduced. Mild side effects were noted in 5 patients (15.6%). These results suggest that bromazepam is clinically useful for the treatment of vertigo or dizziness. A questionnaire consisting of 14 questions was used to evaluate handicaps in the patient's everyday life due to dizziness. It appeared that bromazepam reduced these handicaps by improving both mood disturbances and limitations of physical activity due to dizziness.
The response of cerebral blood flow to changes in the carbon dioxide partial pressure (i.e., CO2 reactivity) has been evaluated as a parameter of cerebral perfusion reserve in patients with vertigo by transcranial Doppler ultrasonography (TCD). We have examined the mean blood flow velocity (FV), and CO2 reactivity of basilar artery (BA) by TCD. Nine patients with cerebral infarction, 46 patients with vertebrobasilar insufficiency (VBI) (17 vascular VBI and 29 hemodynamic VBI), 29 patients with peripheral vertigo, 46 patients with vertigo of unknown origin and 14 normal subjects were enrolled in this study. CO2 reactivity in patients with cerebral infarction and vascular VBI was significantly lower than that in normal subjects. These findings demonstrate that CO2 reactivity measured by TCD evaluates the insufficiency of cerebral circulation in vertigo patients.
This study investigated the characteristics of postural sway in cases of Parkinson's disease (PK). We previously reported sway patterns, its measurements, and factor analysis. This paper investigates learning and evaluation by neural networks. Each subject stood on a stabilometer with their eyes open or closed, and the sway of the center of gravity was recorded for one minute. The learning and evaluation was performed using a neural network program developed by Anima corporation. Input data were 6 units (measurements values related to area and length) in analysis A and 20 units (measurements values related to area and length, power spectrum, vector of velocity, amplitude probability density distribution curve) in analysis B. Output consisted of 3 units (positive, negative a, and negative b symptoms) in both analyses. There were 16 subjects, of whom 13 were used for learning and 3 for evaluation. Learning was carried out until the number of learning trials reached 10000, or the square error margin decreased to 0.005. Results 1) In analysis A, learning revealed a square error margin of 0.005 after 690 trials, while the evaluations revealed a square error margin of 0.263. 2) In analysis B, learning revealed a square error margin of 0.005 after 215 trials, while the evaluations revealed a square error margin of 0.267. Three symptoms were classified clearly as results of learning in analysis A and B. The number of learning trials in analysis B was less than that in analysis A, indicating that increased input resulted in fewer learning trials. The square error margin for evaluation was not good in either analysis.
Morphological aspects of the vestibular end-organs, especially the otolith organs should be considered three-dimensionally when the functions of these organs are dis cussed. In this study, the saccular maculae and the other parts of the vestibular end-organs, from serial sections of human temporal bone which was sectioned horizontally at a thickness of 20 μm, were reconstructed three-dimensionally using a computer with 3-D software (Ashlar Vellum 3D). Every fifth section was stained with hematoxylin and eosin from the level of the lateral semicircular canal ampulla to the posterior semicircular canal ampulla, while every tenth section was stained in the other portion. When the saccular maculae were presented in temporal bone sections, coordinating markers were placed every 100 μm, and triangles were drawn using those markers on the surface of the saccular maculae. A total of five hundred and twenty-two triangles were constructed on the entire surface area of the saccular maculae. Using data from measurement of those triangles, the equations of each plane of the triangle and the angles between each triangle and each standard plane (the sagittal, horizontal and frontal planes) in the stereotaxic coordinate system were developed and calculations solved. The median, maximums and minimums of the angle were (27.2°, 66.5°, 1°), (71.5°, 89.9°, 33.9°) and (76.2°, 89.9°, 46.9°), respectively. The above results were based on the measurements of one temporal bone specimen. There are probably some variations among temporal bones, and we plan to reconfirm the above findings using at least three additional temporal bone specimens in the future. This study is supported in part by NIH/NIDCD Grant DC00589 and the Japan Foundation for Aging and Health.
Quantitative analysis of stress levels in 336 persons (as control) and 19 patients with Meniere's disease was performed by questionnaire. The questionnaire inquired into causes of stress and personality characteristics (type A, self-restraint, escape) related to stress. Scores for causes of stress and personality characteristics in 19 patients with Meniere's disease for two years or less was significantly high compared with those in 336 other persons. These results suggest that stress may be one of the factors related to the onset of Meniere's disease. A questionnaire regarding quantitative analysis of stress levels may be very useful for psychological therapy in patients with Meniere's disease.
Spatial orientation is influenced by many factors such as vision, hearing, vestibular input, and so on. However, the details of when and which factor exert influence on this process remain mostly unknown. We investigated the influence of height on spatial orientation under various conditions. Body movement was recorded by stabilometry for 30 seconds under each of three visual conditions (eyes open without gaze fixation, eyes closed, and eyes open with gaze fixation) at 0 m, 1 m, 2 m, and 10 m22 cm high in 30 normal volunteers (14 males and 16 females) who had no history of vertigo or dizziness. Eight of subjects claimed to be acrophobic. The total length of the gravity center movements reflected the body sway best. The sway was minimal with eyes open and gaze fixated, and maximal with eyes closed. The sway increased at 10 m22 cm high, but was almost the same at 1 m and 2 m high. The acrophobic group was clearly worse than the non-acrophobic group at 10 m22 cm high. Their total shifting length increased because they became tense and shivered fractionally. Visual information which served as the base was useful for spatial orientation, and the mental factor of fear caused tension and the sway increased especially in the acrophobic group at 10 m22 cm high.
This study investigated the effect of hyperventilation on caloric nystagmus. Caloric test using cool air (15°C, 6 l/min) was performed in 14 normal volunteers. Each volunteer underwent caloric test twice. One was performed without hyperventilation, while the other was performed after hyperventilation for 60sec. We used maximal slow phase eye velocity and slow phase eye velocity at the time of the cessation of caloric stimulation (initial slow phase velocity) as parameters for electronystagmographic recording. The data from each volunteer were compared and statistically analyzed. Hyperventilation significantly augmented the maximal slow phase eye velocity and the initial slow phase eye velocity.