To study the sense of spatial orientation, understanding the coordinate system of the labyrinth is indispensable. The 100-year-old stereoscopic photograph of the labyrinth shows the three semicircular canals arranged as if a three-coordinate axis. Behavioral observation of canal nerve stimulation 40 years ago disclosed that electrical stimulation of the canal nerve moved the eyes along the canal when the head was fixed. When the head was free to move, it moved the head in the same direction, and it moved the animal in space when the animal was free to move. Stereo-measurements of the labyrinth determined that the semicircular canals are not orthogonal to each other, and the synergistic pairs of canals in the right and left ears are not on one plane. The semicircular canal nerves sent information regarding head rotation velocity on the non-orthogonal canal coordinate axis. A three-dimension analysis of the vestibulo-ocular reflex (VOR) before and after canal plugging enabled precise measurements of semicircular canal contribution to VOR. The summed gain and phases of plugged VOR were comparable to the VOR of normal; LC (four vertical canals plugged) +VC (bilateral lateral canals plugged) =Normal, and RALP+LARP (sum of one pair of vertical canals intact) =VC, however, rotation in light did not change after plugging. These findings indicate that a semicircular canal coordinate system is firm and does not adapt after inactivation, although, sufficiently compensated by vision while moving in light.
Specificity of otolith and canal input was investigated in second-order vestibular neurons (2°VN). Especially the convergence of monosynaptic input from the three semicircular canals, the utricle, the lagena and the saccule was studied. Each of the six nerve branches on one side was stimulated separately in in vitro frog brain preparations. Antidromic spikes evoked from the spinal cord or the oculomotor nuclei were used to further identify the projection of these 2°VN. About 42% of the 2°VN received a monosynaptic input from only one ipsilateral labyrinthine organ. A small number of 2°VN showed a monosynaptic convergence of canal (8%) or of utricular and lagenar inputs (11%) or of utricular and saccule (4%) or lagenar and saccule (5%). Monosynaptic convergence of canal and utricular (24%) or of canal and lagenar inputs (31%) was more frequent. Monosynaptic utricular inputs were observed in 2°horizontal and 2°vertical canal neurons with a ratio of 3:1. Monosynaptic lagenar inputs were detected in 2°vertical but not in 2°horizontal canal neurons. In a separate group of 2°VN the convergence pattern of monosynaptic saccular, canal, lagenar and utricular inputs was studied. A monosynaptic convergence of signals from the saccule and any other labyrinthine organ was observed only in 3% of 2°VN. Descending and/or ascending projections were found for 2°canal and 2°utricular neurons, 2°lagenar neurons projected only to the spinal cord and 2°saccular neurons projected neither to the spinal cord nor to the oculomotor nuclei. The results show that afferent vestibular inputs converge at the level of 2°VN in a canal plane-specific way. Furthermore, these results are consistent with a role of lagenar input for spinal but not oculomotor reflexes and a non-vestibular function of saccular input in the frog.
Benign paroxysmal positional vertigo of the horizontal semicircular canal (HC-BPPV) is characterized by direction-changing nystagmus. Geotropic transient positional nystagmus is caused by canalolithiasis, and apogeotropic persistent positional nystagmus is caused by cupulolithiasis of the horizontal semicircular canal. The Lempert method of particle repositioning maneuver is effective for the treatment of HC-BPPV of canalolithiasis. However, the effectiveness of the Brandt-Daroff method for the treatment of HC-BPPV of cupulolithiasis is limited, because its mechanism is non-specific. Some methods such as mastoid oscillation of the affected ear or head shaking were reported to detach the otolith clot from the cupula into the canal. The transition of cupulolithiasis to canalolithiasis followed by the Lempert method may be effective for the treatment of cupulolithiasis of horizontal semicircular canal. Because the first step of the Lempert method is head rotation toward the unaffected ear, identification of the affected ear is indispensable for successful maneuver. Canalolithiasis of the horizontal semicircular canal induces ampulofugal endolymphatic flow by a change in head position from upright to supine, resulting in nystagmus beating toward the unaffected ear. Positioning nystagmus is the most useful index to identify the affected ear in canalolithiasis. To identify the affected ear in cupulolithiasis, positional nystagmus in the supine position is the most useful index. Based on the CT imaging of the inner ear, the cupula of the horizontal semicircular canal is not precisely aligned with the sagittal plane of the head, but with a plane rotated medially around the Z-axis at an angle of about 14 degree. Therefore, cupulolithiasis of the horizontal semicircular canal induces nystagmus beating toward the affected ear when the patient is in a supine position.
The primitive hypoglossal artery is one of the embryological vessels that connect the carotid and basilar arteries. It persists occasionally after birth, but the persistent primitive hypoglossal artery (PPHA) is an uncommon vascular anomaly. In this paper, we describe a case of acute vertigo with PPHA. A 54-year-old man complained of vertigo when he turned his head while riding the train. A few minutes later, he lost consciousness for 2 hours. He was treated with medication at a local hospital, and there was improvement of his symptoms. However, he remained concerned about the sensation of dizziness, and presented to the neurotological clinic at Takarazuka City Hospital on March 18, 1999. Spontaneous rightward tortional and horizontal nystagmus was present. Severe canal paresis was detected on caloric test. Mild cerebellar signs were noted. Eye tracking test, optokinetic pattern test and auditory brain stem response were normal. Vestibular dysfunction with a cerebellar lesion was suggested. Brain MRI did not indicate any intracranial lesions except for apparent absence of the left vertebral artery. MRA failed to show the vertebral arteries bilaterally, but detected the anastomotic artery that communicated between the right internal carotid artery and the basilar artery. Carotid angiography indicated similar findings. MRA indicated that the vessel ran through the hypoglossal canal. These findings demonstrated that the anastomotic artery was the PPHA. In this case, the basilar artery was only perfused via the right carotid artery. Insufficiency of the carotid artery might occur when the patient turned his head, resulting in basilar insufficiency, syncope and vertigo.
Homonymous hemianopia is caused by lesion of in the contralateral optic radiation or visual cortex in cerebral hemisphere or as the result of vision obstacle occurring in the area of striata damage. It is known that the influence of the cerebral hemisphere on eye movement related to pursuit, OKN. We compared ENG and eye-head coordination in two cases of congenital and acquired hemianopia due to left occipital lesion. In ENG of two cases, saccade was overshot on movements toward the blind side, pursuit was saccadic on movements toward the normal side and the OKN was defectiveness contralateral to the damage. However, any recordings in the congenital case were much worse. In eye-head coordination tests of these two cases it was demonstrated that the gaze movements toward the blind sides the disorders were greater before fixation. The visual fixation of the acquired case was more damaged than that of the congenital case.
Since the publication of the article entitled "Placebo effect in surgery for Meniere's disease. A double-blind, placebo-controlled study on endolymphatic sac shunt surgery" by Thomsen et al. in 1981, endolymphatic sac surgery for Meniere's disease has tended to receive a lower evaluation. Investigators who read only its abstract were likely to understand that this study was well planned and performed under a doubleblind, placebo-controlled study and that the conclusion would be reliable. The results showed that only a minor difference (p<0.05) was observed between endolymphatic sac surgery (active groups) and mastoidectomy (placebo group), and, in contrast, the greatest difference (p<0.01) was found in both groups when preoperative and postoperative scores were compared. Thomsen et al. concluded from their results that the great difference (p<0.01) between preoperative and postoperative scores in each surgery was more important than the minor postoperative difference (p<0.05) between the two surgeries. In this study, however, they made a mistake in which p-value derived from paired-test was compared with the p-valued derived from the non-paired-test. They neglected the postoperative difference (p<0.05) between the two surgeries. Therefore, their conclusion would be wrong. Our statistical reevaluation demonstrated that endolymphatic sac surgery (active group) was more effective than regular mastoidectomy (placebo group) in some aspects such as dizziness & vertigo, total scores, tinnitus, 250 Hz hearing threshold and AAOO evaluation. We must also note that Thomsen et al. were strongly influenced by Tork who considered that any treatment has 60-80% effectiveness in Meniere's disease. Thus, Thomsen et al. initiated this study expecting that endolymphatic sac surgery would have non-specific placebo effect. Finally we have to add that their research using human beings was a violation of the Helsinki Agreement on Medical Ethics in 1964.
The Galvanic test has been studied as a test of equilibrium. However, it has been less applied clinically than other tests, partly because analysis of the ENG records is difficult due to contamination by electric stimulation. In this study, to overcome this problem, we recorded and analyzed galvanic nystagmus using infrared video-oculography. The subjects were 14 healthy volunteers (8 males and 6 females; mean age 32.6 years). Electrodes were taped to the mastoid processes in both ears. The right electrode was the cathode, and the left electrode was the reference electrode. Direct current stimulations at 1, 2, 3, and 4 mA each with a 30 second duration were applied using a direct current stimulator. Nystagmus was provoked toward the cathodes in all subjects. The threshold of provocation was 1 mA in 10 and 2 mA in 4 of 14 subjects. The average frequency of nystagmus was 0.645 Hz at 1 mA, 1.088 Hz at 2 mA, 1.348 Hz at 3 mA, and 1.592 Hz at 4 mA. The average slow phase velocity was 2.121, 5.053, 7.564, and 9.130 deg/sec, respectively. Both the frequency of nystagmus and average slow phase velocity tended to increase linearly with the intensity of the electric current. Since nystagmus was provoked toward the cathode, the cathodic current is considered to have increased the firing of the vestibular afferent pathway. Zinc et al., who performed experiments using an infrared video-oculography and a similar stimulation pattern, reported that there was a difference in the threshold of provocation by galvanic vestibular stimulation between the otolith and semicircular canal. According to our results, nystagmus was provoked at 1-2 mA, and the threshold of provocation by galvanic stimulation is not considered to differ between the otolith and semicircular canal.