Imaging studies in humans have confirmed the existence of several separate and distinct vestibular cortical areas, which had been identified earlier by tracer and electrophysiological studies in experimental animals. The most robust cortical vestibular structures in monkeys are the parieto-insular vestibular cortex (PIVC), the visual temporal sylvian area (VTS) in the retroinsular cortex, the superior temporal gyrus (STG), the inferior parietal lobule (IPL), the anterior cingulum, the hippocampus and area 6a. All belong to a multisensory vestibular cortical circuit. The PIVC seems to be a dominant multi-modal vestibular cortex area in monkeys and it is considered the ’core region’ within this network. During the last 10 years, many positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies using vestibular, somatosensory and visual optokinetic stimulation have revealed that such multisensory vestibular cortical areas are located in similar sites in humans. In addition, a reciprocal inhibitory cortical interaction has been observed between different sensory systems, such as the inhibitory visual-vestibular interaction. This interaction provides a powerful means for shifting the dominant sensorial weight from one modality to the other for resolving conflicts between incongruent sensory inputs. In this article, fMRI studies on cortical processing of vestibular sensation and spatial orientation were reviewed.
A case of congenital anidiria with congenital nystagmus was reported. In his family, similar symptoms of anidiria and nystagmus were observed on eight members over three generation. Hereditary anidiria was transferred in autosomal dominant pattern in this pedigree. Nystagmus of this case was not supressed with closed eye, and may be of mixed origin of peripheral anterior visual pathway and central nervous system, as in albinism. Recent articles demonstrated that PAX6 gene was responsible for hereditary anidiria and congenital nystagmus. PAX6 gene has a role in movement of neural cells during development, as responsible gene of albinism has.
The effect on the vestibulo-ocular reflex (VOR) is evaluated by using a caloric stimulation in which the ears of subjects in the supine position are irrigated with water or air. Studies on the clinical application of caloric stimulation have shown that the stimulation results in a gentle rise of VOR response, which does not precisely reveal the time course of VOR onset. In our study, 14 healthy subjects were evaluated with a step stimulus technique, which showed the onset and offset of caloric stimulation with a rapid change of the position of the subject's head during continuous irrigation of his or her ear. The technique showed a rapid rise (indicating an activation) and consequent gentle attenuation (indicating a compensation) of VOR response. On-step (from sitting to supine position) and off-step (the opposing maneuver) stimulation delivered the same characteristics of this rise and attenuation with opposing direction, through the ampulo-petal and ampulo-fugal convection along their lateral semi-circular canals respectively. Repeated ipsi-lateral stimulation with an interval of 4 minutes caused an increased adaptation of VOR during the on-step response. Some possible reasons for these results might be the occurrence of a central adaptation of VOR or a mechanism involving the peripheral vestibular apparatus such as depletion of the synaptic transmitting substance. Step stimulus of one side did not demonstrate any contribution to subsequent contra-lateral stimulation with the same 4-minute interval. This finding supports the idea that the peripheral vestibular system contributes to the adaptation of VOR. Introducing this step stimulus technique into the clinical examination setting would facilitate the elucidation of the pathophysiological basis of vestibular deficits.
Seventy-two patients with dizziness or vertigo having C4-7 cervical disk disease had their systolic blood pressure (BP) measured before and after the head-up test with tonometry. We demonstrated that significant depression of the systolic BP was seen in the patient group compared with the normal group during the head-up test. There were 11 patients in whom vertigo or dizziness was induced by each head-up test, and all of them showed a BP depression of 19 mmHg or more. However, 26 patients had a BP depression of only 9 mmHg or less, which was within normal limits, and none showed vertigo or dizziness. It was considered whether the main cause of vertigo or dizziness induced by the head-up test among the patients with cervical lesion was BP depression. The other causes of vertigo or dizziness among the patients who showed BP depression of 18 mmHg or less could possibly be blood flow insufficiency in the brain stem, acoustic nerve ischemia, Powers syndrome, carotid artery stenosis, platelet hyper-aggregation or psychosomatic factors.
The relationship between dizzy patients and stress is well documented, but that between dizzy patients and sleep disturbance is unclear. This study focused on sleep disturbance in dizzy patients through investigations into their hypnotic medications. Six hundred and twenty two patients were studied, who complained of dizziness and visited Nagoya City University from January 1 to December 31, 2007. The major hypnotic was the benzodiazepine group (65%), and was prescribed to 226 patients (36%). Although prescription of hypnotics tended to increase with the age of the subjects, it was even prescribed often in young adults. The approximate ratio of patients taking hypnotics to those who were suffering from insomnia and without dizziness was 2:1. Poor quality of sleep may cause additional stress, leading to a vicious cycle in patients suffering from dizziness.
In treating patients with Ménière's disease, isosorbide, one of the osmotic diuretics, is an essential drug to reduce endolymphatic hydrops. However, isosorbide liquid tastes bad, and tends to reduce patient compliance for taking this drug. To solve this problem, isosorbide jelly has been developed. Although the taste has still problems, isosorbide jelly has the advantage that it can be conveniently carried in a handy pack. In this study, we compared the compliance in 16 Ménière's patients between taking isosorbide liquid in bottles and individual handy packs. Patients were also asked to comment on the differences in taste between isosorbide liquid and isosorbide jelly. It was hypothesized that the patient compliance for the packed products would be better than bottled ones so that dizziness handicaps would be reduced in patients who were prescribed the packed products. The results showed patient compliance for the packed products was significantly better than that for bottled ones and that the dizziness score was significantly lower in patients in whom the packed product was prescribed. Four of 5 patients had the impression that isosorbide liquid tasted better than isosorbide jelly. We concluded that isosorbide liquid tasted better than isosorbide jelly and that the packed products were superior to bottled ones in terms of patient compliance in taking the drug. At this stage, isosorbide liquid in packs is the most recommended osmotic diuretic in terms of ensuring patient compliance with their medication when treating Ménière's patients.