Pause neurons (PNs) are inhibitory neurons in the medial pontine reticular forma-tion which fire tonically and cease firing about 20 ms prior to quick eye movements in all directions. Anatomical and physiological evidence from cats has shown that these neurons (1) project and terminate on two groups of burst neurons involved in the genesis of horizontal saccadic eye movements: inhibitory burst neurons (IBNs) and excitatory burst neurons (EBNs), (2) project to the caudomedial subthalamus: the nucleus of the Field of Forel containing burst neurons which relate to vertical eye movement, (3) project to other reticular formation neurons from the midbrain to medulla, and (4) project to the upper cervical cord. PNs play an important role in the quick eye movement aspect of gaze control; and may also play a role in quick head movements which are related to gaze control. This paper mainly describes anatomical evidence of the trajectory of single PNs and the projection of PNs to various eye movement-related areas in the brain stem, using intra-axonal staining with horseradish peroxidase and micro-injection of the tracer Phaseolus vulgaris leucoagglutinin.
This article reviews the nucleus prepositus hypoglossi (NPH) which has been proved to contribute to generation of horizontal eye movements. In general, the NPH receives inputs from oculomotor related nuclei (e.g. the bilateral NPH, the medial vestibular nucleus and ipsilateral burst neuron areas), and projects directly to the bilateral NPH, the vestibular nuclei, the ocular motor nuclei and vestibulo-cerebellar structures. According to these different neural connections, the NPH has been divided into subdivi-sions. Several types of neural activities relating to eye movements are observed in NPH neurons, most of which are increased during ipsiversive horizontal eye movements. The majority of the neurons encode both eye velocity and position signals (burst-tonic neurons). Some of the neurons project to the abducens nucleus. In addition, a class of NPH cells show a burst of activity during a variety of rapid eye movements in cats (burster-driving neurons). These neurons receive disynaptic vestibular input contralaterally and project to burst neuron areas. There are also NPH cells encoding both eye- and head-velocity signals in monkeys (eye-head-velocity neurons). Lesions of the NPH impair gaze holding, implying that the NPH functions as, at least a part of, the neural integrator. However, saccade feedback and putative smooth-pursuit integrators are not influenced after a partial lesion in the NPH. The results suggest that distinct classes of cells spread over the NPH. In summary, the NPH is involved in several aspects of horizontal eye movements and may also function as a part of the neural integrator.
Using the rats with ischemia induced by occlusion of the anterior inferior cerebellar artery (AICA) or vertebral artery (VA), we investigated the auditory brainstem response (ABR), electrocochleogram and caloric tests. Upon occlusion of the VA, there was no change in the ABR, whereas in the caloric test the duration of nystagmus on stimulating both ears shortened. After occlusion of the AICA, ABRs were classified into three patterns: all components disappeared: n=4; all components disappeared transiently and then recovered: n=2; the interpeak latency between I and IV wave increased: n=7. Upon occlusion of the AICA, the cochlear blood flow (CoBF) showed one of three pat-terns of change: no change: n=5; decrease: n=10; and transient decrease with recovery: n=5. The cochlear potentials were dependent on residual CoBF. In the caloric test, when the left AICA was occluded, the duration of nystagmus induced by stimulation of the left (ipsilateral) ear was shorter than that induced by the right (contralateral) ear. Based on the functional test results, we conclude that in this model of ischemia the function of the vestibular system including the semicircular canal is more severely affected than the hearing function.
Coriolis stimulation evokes severe motion sickness, accompanied by various eye movements, auotonomic nervous symptoms and disorders of spatial orientation. In this study, we performed 2 experiments to evaluate the relationship between the severity of motion sickness and eye movement response to Coriolis stimulation as well as the relationship between disorders of spatial orientation and eye movements and to elucidate the mechanism that generates Coriolis-induced eye movements. Experiment 1 was performed on 12 subjects ranging in age from 20 to 34 years. Eye movements were recorded by a CCD view camera and electronystagmogaphy when subjects tilted their heads on a rotating chair (120°/sec) in invisible surroundings. As regards autonomic nervous symptoms and disorders of spatial orientation during stimulation, there was a great variation in susceptibility among 12 subjects. Disorders of spatial orientation induced by abnormal inputs of Coriolis stimulation, evoked eye movements and autonomic nervous symptoms. While spatial orientation continued to be influenced by Coriolis stimulation, autonomic nervous symptoms, which functioned as an alarm against disorientation, became severe. In experiment 2, the subject first tilted his head, backward and forward repeatedly, and then, leftward and rightward repeatedly. We analyzed eye movements under these two conditions. While forward and backward tilting head movements evoked torsional eye movements, leftward and rightward tilting head movements evoked vertical eye movements. The axis of eye rotation vector induced by Coriolis stimulations accorded closely with the direction of acceleration vector generated by head tilting and was well explained by vector analysis.
Ménière's disease in children comprises only a small percentage of all patients of Ménière's disease, and is known to be quite rare. A juvenile patient who has been followed for more than 8 years is reported in this paper. This 18-year-old female patient was brought to our department when she was 9 years old with a chief complaint of right-side hearing loss. She had a history of paroxysmal rotatory vertigo with accompanying headache twice per year since she was 5 years old. Right-side hearing loss and tinnitus had been noted since she was 9 years old. The hearing loss and the tinnitus were aggravated during the attacks of vertigo. Physical examinations revealed low-tone perceptive hearing loss of about 43 dB on the right ear. Caloric test revealed right canal paresis. Glycerol test results were positive. Since the vertigo attacks were episodic, and the equal-loudness contours on three-dimensional audiogram showed that aggravated hearing loss fluctuated despite medication, the patient received right-side intratympanic gentamicin injection when she was 16 years old. To date, vertigo has subsided for more than 2 years since the intratympanic injection.
Click-evoked myogenic potential of cervical muscle to intense clicks shows a characteristic short-latency positivity-negativity, and it is thought to be due to vestibulo-collic reflex. In this study, in order to evaluate the origin, myogenic potential and caloric response were compared among 4 dizzy patients. In the first two case (right delayed endolymphatic hydrops and right acoustic tumor), the myogenic potential to the click of affected ear was normal, while caloric testing revealed a high CP % (71% and 53%). In the remaining two cases (right Meniere's disease and left acoustic tumor), myogenic response was abnormal compared with low CP % (21% and 29%). These discrepancies between myogenic potential and caloric response suggest that click-evoked short-latency myogenic potential may be dependent on lateral semicircular canal function.
To determine criteria for evaluating the vertebrobasilar arterial system (VAS) by magnetic resonance angiography (MRA), we examined 43 vertiginous cases by MRA. We divided those cases into two groups, the vertebrobasilar insufficiency (VBI) group and the non-VBI group according to clinical diagnoses. MRA results were assessed based on the severity of stenotic changes in the three major VAS arteries, the bilateral vertebral arteries and the basilar artery. The MRA score was defined as the total score of those three arteries in each case, and the severity score was classified in 3 stages (1:ir-regularity, 2:stenosis, 3:interruption). Then we statistically analyzed the correlation between the MRA score and patient's age, between the MRA score and whether a patient has any complications connected with arterial sclerosis or not, and between the MRA score and clinical diagnoses. On statistical analyses, there was no correlation between the MRA score and patient age, or between the MRA score and complications. However, the MRA scores of the VBI group were significantly higher than those of the non-VBI group. These findings indicate that evaluation of stenotic changes in the VAS by MRA might provide useful information for diagnosing VBI.
It is difficult to estimate individual performance in sports because of the complicated relationship of various reflexes, accommodation and mental state. To clarify that part of sports ability, we investigated the effect of horizontal optokinetic stimulus training on body balance. Experiment A: Male subjects were stimulated optokinetically to the right on stabilometer. The angular velocity of the Ohm type drum was 60 deg/sec and the dura-tion of the stimulation was 60 seconds. This training was conducted twice a day for 4 weeks. Before and during this training, we performed the test every week and then again after a rest period of 2 weeks. Total length, x part (stimulus direction) length, area of sway, locus length per limit area were calculated. These parameters decreased after 2 weeks and were maintained after a period of 2 weeks except for locus length per limit area. Experiment B: Male subjects were trained as in experiment A and compared with high school baseball players. High school baseball players have a good control of balance as shown in the x part (stimulus direction) and locus length per limit area compared to those in male subjects. Experiment C: Male subjects were stimulated optokinetically to the right while sitting on a chair and findings were compared to those in male subjects who served as control. The drum was rotated with an acceleration of 2 deg/sec2 and this training was conducted twice a day for 3 weeks. Before and after this training, we performed this test. We found out that training while seated on a chair stabilized body balance.
Personal backgrounds are very important in determining the cause of vertigo or dizziness. This study investigated the effects of personal and daily backgrounds on vertiginous patients. Mainly, patients with inner ear lesions and dizziness were examined in this study. Their chief complaints were dizzy, rotatory vertigo, positional vertigo, etc. The results of CMI examination were type I 36%, type II 32%, type III 22%, type IV 10%. Habitual alcohol consumption: no drinking or could not drink 61%, habitual drinking 39%. Sleeping: trouble 54%, good 46%. Motion sickness: yes 51%, no 49%. To prevent vertigo, it is very important to improve the personal and daily life style of patients. The following factors are especially important. 1. To improve sleeping trouble. 2. To take more exercise and have a relaxing hobby. 3. To eat breakfast. 4. A certain level of alcohol consumption is good for health, but smoking should be stopped. 5. To improve motion sickness.