Vestibular compensation, the behavioral recovery that occurs following the removal of afferent input from one vestibular organ or nerve, is a useful experimental model of lesion-induced plasticity in the central nervous system. While the recovery of resting activity in the vestibular nuclei ipsilateral to the lesioned side is involved in the process of vestibular compensation, the neuropharmacological mechanisms underlying neuronal recovery are unknown. This review focuses on the pharmacological basis of vestibular compensation to clarify the changes in the neurochemical or synaptic organization of the vestibular nuclei and discusses the neurochemical mechanisms underlying the development of vestibular compensation.
Five patients with cochlear Meniere's disease who exhibited vertigo caused by stress are reported. A hearing test in all patients revealed low-tone sensorineural hearing loss and their symptoms improved with medication although the hearing loss recurred for a while. The patients were diagnosed with cochlear Meniere's disease. All cases had exhibited vertigo from the onset of increased stress. A 42-year-old man had been complaining of tinnitus and ear fullness since he lost his job and the first vertigo attack occurred when his unemployment benefit finished. A 66-year-old woman complaining of hearing loss and tinnitus had been suffering from vertigo since she started living with her mother-in-law, who was on bad terms with her. A 62-year-old man who had been suffering from repetitive tinnitus started exhibiting vertigo when he started taking care of his aged mother. The other 2 patients also felt vertigo after the start of stressful situations. In our questionnaire 3 patients showed type A personality, which indicates a hypersensitivity to stress. We report 5 cases of vertigo attacks in patients with cochlear Meniere's disease due to stress. The psychosomatic approach of our questionnaire may be effective to evaluate stress in patients.
The purpose of this study was to clarify the influence of daily resistance exercise during bed rest, using a one-foot balance test. Eight healthy subjects were confined to bed for 20 days and physical exercise was restricted to a minimum. Three non-training group subjects remained at a -6 degrees head-down tilt throughout the bed rest period. Five training group subjects also remained at bed rest, except during resistance exercise, which was carried out every morning. A one-foot balance test was performed immediately prior to and after the bed rest. The subjects were tested six times: three times with eyes open, and three times with eyes closed. Subjects were examined for how many seconds within 60 seconds they could stand on one foot during each visual condition. In the pre-test all subjects could maintain standing for 60 seconds with their eyes open. In the post-test with their eyes closed, none of the controls were able to maintain standing for 60 seconds. Three out of 4 subjects in the training group who could stand for 60 seconds with their eyes open, were also able to stand for 60 seconds with their eyes closed. The results of this study suggest that bed rest effects the ability to use visual information effectively to maintain balance, and that these effects can be countered by a daily exercise program.
The aim of the present study was to determine the optimal visual target to be used in stabilometry. The sway of the body (total length and area of the center of pressure) was measured on 30 healthy subjects while they were shown 8 kinds of visual targets at random, placed 2 m infront. The body sway was also measured on subjects with their eyes closed in light conditions; and with their eyes open but with no target. The results showed that, in contrast to the reports by other authors, the body sway was smallest when there was no target. The body sway was largest with the eyes closed, as previously reported. The results obtained using different target shapes (closed circle or cross) or sizes were not significantly different. We speculate that when the subject focuses on a specific target, his/her attention is concentrated on the central view, and input from the periphery may be reduced. Thus, we conclude that it is optimal for the subject to gazes at no specific visual target in stabilometry.
This study investigated the relationship between static balance scores and muscle strength in older adults. The subjects were 618 older adults (male 259, female 359) aged 67 to 91 years living in Nangai Village in Japan. 1) Body sway test: The subjects stood stationary and upright on a force platform with their feet together (Romberg stance) for 20 seconds with eyes open and eyes closed. Body sway length and body sway area were calculated as magnitude of body sway. 2) One leg standing: Duration of standing while using the preferred leg was measured for a maximum of 60 seconds with eyes open, and for 30 seconds with eyes closed. Muscle strength: The grip strength of the preferred hand was measured using a hand-held Smedley-type dynamometer as muscle strength. Among the three balance scores with eyes open, the most significant relation to grip strength was the one leg standing score. The relationship between muscle strength and body sway area with eyes open was significant, but that between muscle strength and body sway length with eyes open not significant. The relationship between grip strength and the balance scores with eyes closed was not clear.
Axonal pathways and the projection levels of posterior-semicircular canal (PC)-ac-tivated vestibulospinal neurons were studied in decerebrated and anesthetized cats. The PC nerve was selectively stimulated by bipolar silver electrodes. Two monopolar electrodes were inserted into the lateral vestibulospinal tract (LVST) and medial vestibulospinal tract (MVST) to determine the pathway of axons. Three pairs of similar electrodes were positioned in the C2-3, C7-T1 and T12-L3 segments to examine projection levels. Another monopolar electrode was placed in the oculomotor nuclei to determine whether PC-nerve-activated vestibulospinal neurons s have branches ascending to the oculomotor nuclei. Fifty six neurons were activated orthodromically after PC nerve stimulation. Ten PC-nerve-activated vestibulospinal neurons were also antidromicaly activated from the oculomotor nuclei. All of these vestibulo-oculo-spinal (VOS) neurons descended through the MVST and terminated in the upper cervical segments. Eighteen PC-ner-ve-activated vestibulospinal neurons descended through the LVST, 45% of which reached upper lumber segments. Fourteen vestibulospinal neurons descended through the MVST. Most of these terminated in upper cervical segments. These results suggest that VOS neurons convey posterior semicircular canal signals to both the ocular and neck motor centers, linking eye and head movement.
We previously investigated disabilities in daily living in patients with unilateral vestibular disorders. The largest number of patients reported difficulty in pulling on their pants or skirt while standing on one leg. Many patients also answered that they felt unstable when turning their head while standing or walking. However, it has been difficult to detect their disability using current methods such as electronystagmography, stabilometry and so on. The purpose of this research was to develop a motion analysis system to detect the effects of vertigo on activities of daily living. Sixteen healthy subjects, 7 males and 9 females, took part in this study. Fluorescent markers were attached to the subject's head, shoulder, elbow and greater trochanter. The chair that the subjects were sitting on was rotated for 10 seconds to induce vertigo. The seven females went through the motions of pulling on a skirt before and after stimulation. These motions were recorded by CCD camera and each position of the body was calculated and stored on the hard disk of the computer. The angle between shoulder line and a horizontal line on the monitor was measured. Two other females and 7 males looked behind themselves before and after stimulation. The degree of each fluorescent marker's rotation around the vertical axis was estimated from the distance of movement of the head, shoulder and elbow. In both of the motions, the effects of vertigo could be clearly observed. From our experiments, we suggested that motion analysis is a useful method for detecting disa-bility in the activities of daily living of patients with vertigo.
Postural tachycardia syndrome (POTS) has recently been recognized as a syndrome in which patients have an increased heart rate without orthostatic hypotension. Patients with POTS may complain of presyncope, vertigo, dizziness, light-headedness, general fatigue or unsteadiness. However, the etiology of POTS is unclear. We report a typical case of POTS; a 24 year-old woman who had suffered from dizzy sensations during postural changes for six months. No abnormalities had been observed in ECG, echocardiography, clinical chemistry, blood test and brain MRI. On the first visit, no abnormal responses were noted on neuro-otological examinations or for the CMI and SRQ; D psychological questionnaires. However, the patient's heart rate increased by 34 beats/min from supine to standing position, and in addition, she complained of a headache and fatigue without hypotension during Schellong test. Power spectral analysis of RR interval variability during Schellong test revealed that the normalized powers of low frequency (LFnp) and ratio of LF and high frequency powers (LF/HF) increased when standing upright from supine position. We diagnosed her with POTS and administered atenolol (β1 blocker, 50mg every morning) in formula, which markedly reduced her subjective symptoms.