Vertical canal function in normal subjects and patients with benign paroxysmal positional vertigo

OBJECTIVES: To assess the dynamics of the vertical semicircular canal (VSCC)-ocular reflex in normal subjects and then to compare their gain in VSCC-ocular reflex with that of patients with benign paroxysmal positional vertigo (BPPV). MATERIAL AND METHODS: Subjects were sinusoidally rotated around the earth-vertical axis with their head tilted 60 degrees backward and turned 45 degrees to the right or left side from the sagittal plane at frequencies of 0.1, 0.3, 0.5, 0.7 and 1.0 Hz with a maximum angular velocity of 50 degrees/s. Head rotation to the right side on the right anterior semicircular canal (SCC)-left posterior SCC plane or to the left side on the left anterior SCC-right posterior SCC plane stimulated the pair of VSCCs. Eye movements were recorded on a video imaging system with an infrared charge-coupled device camera, using our new technique for analyzing the rotation vector of eye movements in three dimensions. RESULTS: The mean gains in left posterior SCC-ocular reflex in normal subjects ranged from 0.44 at 0.1 Hz to 0.79 at 1.0 Hz, while the mean gains in right anterior SCC-ocular reflex ranged from 0.45 at 0.1 Hz to 0.73 at 1.0 Hz. The mean gains in right posterior SCC-ocular reflex in normal subjects ranged from 0.53 at 0.1 Hz to 0.89 at 1.0 Hz, while the mean gains in left anterior SCC-ocular reflex ranged from 0.53 at 0.1 Hz to 0.88 at 1.0 Hz. Thus, the gains in VSCC-ocular reflex did not differ among the four VSCCs in normal subjects. Similarly, vestibulo-ocular reflex (VOR) gains of the four VSCCs in patients with right- or left-sided BPPV were almost the same at all frequencies compared to those of normal subjects. CONCLUSION: In patients with BPPV, gains in VOR in the four VSCCs were not changed in comparison with those of normal subjects. It is suggested that the mass of free-floating otoconial debris associated with canalolithiasis was too small compared to that of the endolymph to change the canal dynamics.     

Computer-aided three-dimensional reconstruction and measurement of semicircular canals and their cristae in man

We studied the spatial relations of the semicircular canals (SCCs) and their cristae, by computer-aided three-dimensional reconstruction, a graphic method we developed. The angles between pairs of SCCs, between pairs of SCC cristae, and between a SCC and its crista were measured using histology sections of a normal temporal bone from a 14-year-old female. Angles between pairs of SCCs and pairs of cristae deviated 11.3 to 18.2 degrees and 4.8 to 18.0 degrees, respectively, from right angles and the long axis of each crista deviated 25.0 to 30.4 degrees from the line perpendicular to the plane of the corresponding SCC; thus none of these structures lies at a right angle to another. We believe these new anatomical findings will help in the clinical evaluation of SCC function.     

Planer orientation of the bilateral semicircular canals in dizzy patients

Objective

Recent development of 3-dimensional analysis of eye movement enabled to detect the eye rotation axis, which is used to determine the responsible semicircular canal(s) in dizzy patients. Therefore, the knowledge of anatomical orientation of bilateral semicircular canals is essential, as all 6 canals influence the eye movements.

Subjects and methods

Employing the new head coordinate system suitable for MR imaging, we calculated the angles of semicircular canal planes of both ears in 11 dizzy patients who had normal caloric response in both ears.

Results

The angles between adjacent canal pairs were nearly perpendicular in both ears. The angle between the posterior canal planes and head sagittal plane was 51° and significantly larger the angle between the anterior canal planes and head sagittal plane, which was 35°. The angle between the horizontal canal plane and head sagittal plane was almost orthogonal. Pairs of contralateral synergistic canal planes were not parallel, forming 10° between right and left horizontal canal planes, 17° between right anterior and left posterior canal planes and 19° between the right posterior and left anterior canal planes.

Conclusion

Our measurement of the angles of adjacent canal pairs and the angle between each semicircular canal and head sagittal plane coincided with those of previous reports obtained from CT images and skull specimens. However, the angles between contralateral synergistic canal planes were more parallel than those of previous reports.     

垂直平面摆动试验检测垂直半规管功能及其正常值的研究

目的 利用垂直平面摆动试验检测垂直半规管功能并探讨中青年垂直半规管功能正常值.方法 运用自主研制的SRM-Ⅳ全自动前庭功能诊治系统,采用垂直平面180°正弦非阻尼摆动方法对100名18 ～59岁的健康受试者诱发垂直眼震,记录眼震视频和眼震曲线,采集眼震个数、持续时间、慢相速度等参数.将100名健康受试者以45岁为界分为青年组(68例)和中年组(32例)进行比较.试验中以右前半规管和左后半规管为一对(right anterior semicircular canal and left posterior semicircular canal,RALP),以左前半规管和右后半规管为一对(left anterior semicircular canal and right posterior semicircular canal,LARP),计算出两对垂直半规管垂直眼震平均慢相速度两侧不对称比( canal paresis,CP),采用SPSS 13.0软件进行统计学分析.结果 青年组和中年组平均慢相速度CP值差异无统计学意义(P＞0.05),总体CP值,RALP为10.2％±7.1％,LARP为10.4％±6.2％.健康中青年人群垂直半规管垂直眼震平均慢相速度CP值95％参考值范围,RALP为低于23.7％,LARP为低于22.9％;CP正常范围:≤20％为理想值,20％～ 25％为正常偏高.结论 垂直平面180°摆动试验可有效检测垂直半规管功能,此方法有望在临床得到应用.     

Orientation of Human Semicircular Canals Measured by Three-Dimensional Multiplanar CT Reconstruction

Analysis of vestibulo-ocular reflex experiments requires knowledge of the absolute orientations (with respect to skull landmarks) of semicircular canals (SCC). Data relating SCC orientations to accessible skull landmarks in humans are sparse, apart from a classic study of 10 skulls, which concluded that the horizontal and anterior SCC are not mutually orthogonal (111 ± 7.6°). Multiple studies of isolated labyrinths have shown the inter-SCC angles are close to 90°. We hypothesized that a larger sample would yield mean absolute SCC orientations closer to the mutual orthogonality demonstrated for isolated labyrinths. We measured canal orientations with respect to accessible skull landmarks using 3-D multiplanar reconstructions of computerized tomography scans of the temporal bones of 22 human subjects. Images were acquired with 0.5-mm thickness and reconstructed with in-plane resolution of 234 μm. There was no significant difference between the left and a mirror image of the right (p > 0.57 on multiway ANOVA of orientation vector coefficients), so data were pooled for the 44 labyrinths. The angle between the anterior and posterior SCC was 94.0 ± 4.0° (mean ± SD). The angle between the anterior and horizontal SCC was 90.6 ± 6.2°. The angle between the horizontal and posterior SCC was 90.4 ± 4.9°. The direction angles between a vector normal to the left horizontal SCC and the positive Reid's stereotaxic X (+nasal), Y (+left), and Z (+superior) axes were 108.7 ± 7.5°, 92.2 ± 5.7°, and 19.9 ± 7.0°, respectively. The angles between a vector normal to the left anterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 125.9 ± 5.2°, 38.4 ± 5.1°, and 100.1 ± 6.2°, respectively. The angles between a vector normal to the left posterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 133.6 ± 5.3°, 131.5 ± 5.1°, and 105.6 ± 6.6°, respectively. The mean anterior SCC–contralateral posterior SCC angle was 15.3 ± 7.2°. The absolute orientations of human SCC are more nearly orthogonal than previously reported.     

A new rotational test for vertical semicircular canal function

OBJECTIVE: We developed a new rotating chair in order to assess the function of the vertical semicircular canal (VSCC) by analyzing VSCC-induced post-rotatory nystagmus (PRN). METHODS: We examined 14 healthy subjects, wearing goggles equipped with an infrared CCD camera, and sitting on a chair which was designed to stimulate a pair of the VSCCs by tilting the head 60 degrees backward with a 45 degrees rotation to the left or right side from the sagital plane. The time constant (TC) or maximal slow phase eye velocity (MSPEV) of the vertical component of four kinds of PRN were analyzed in four corresponding rotatory conditions, and used as functional index of the corresponding VSCC. RESULTS: The mean values of MSPEV in both anterior semicircular canal (ASCC) and posterior semicircular canal (PSCC)-induced PRN tended to be lower (P<0.10) than those induced by the lateral semicircular canal (LSCC). The result suggests that the threshold to the angular velocity in the VSCC is lower than that in the LSCC. The mean values of TC in both ASCC and PSCC-induced PRN were significantly lower (P<0.05) than those induced by the LSCC. CONCLUSION: The significant reduction of TC in VSCC-induced PRN compared with LSCC-induced PRN indicates that VSCC function is less affected by velocity storage mechanisms than LSCC function. The rotational test with respect to the VSCC can be used as a tool for assessing vertical canal function.     

迷路下入路开放内耳道手术相关解剖结构的CT测量

目的　为临床上开展迷路下入路开放内耳道手术提供影像学参考信息。方法　选择40例（80侧）正常成人颞骨CT影像资料,对迷路下入路开放内耳道手术的相关解剖标志进行影像学测量。结果　后半规管下端到颈静脉球顶端之间的最短距离平均值为左侧（4.69±2.91）mm,右侧（3.10±3.01）mm,后半规管下部骨质厚度平均值左 侧（0.92±0.37）mm,右侧（0.69±0.37）mm,迷路下区面神经垂直段骨管和乙状窦骨板之间的最短距离平均值左侧（8.66±2.71）mm,右侧（7.74±1.99）mm,颈静脉球顶端到内耳道下界距离平均值左侧（6.32±2.88）mm,右侧（5.39±2.61）mm,颈静脉球顶端到单孔距离平均值左侧（6.82±3.02）mm,右侧（5.84±2.82）mm,前庭导水管开口到内耳门后缘的距离平均值为左侧（14.38±2.56）mm,右侧（14.12±2.76）mm,前庭导水管开口到内耳道中点的距离平均值为左侧（12.02±2.46）mm,右侧（11.91±2.53）mm。前3组测量值左右侧差异有统计学意义,后4组测量值左右侧差异无统计学意义。结论　术前行影像学测量能够为开展 迷路下入路开放内耳道手术提供有价值的信息。     

Three-dimensional reconstruction and measurement of the human membranous semicircular canal

The planar relationship of the human semicircular canals was determined by Blanks et al. at a series of points measured from the dissected bony labyrinth of the human skull. The relationship of membranous canal planes have not, however, been measured from the human temporal bone. We reconstructed 3 semicircular canals by computer-aided 3-dimensional analysis and measured the angles formed between pairs of 3 osseous and membranous canal planes of temporal bones. Five temporal bones in adults were used for this study. Results indicated angles formed between pairs of ipsi-lateral canal planes of both the bony and membranous labyrinth. Angles formed between the horizontal-anterior, anterior-posterior, and posterior-horizontal canal planes of the bony labyrinth were 89.64 +/- 1.82 (mean +/- SD), 90.95 +/- 1.25, and 94.02 +/- 3.77 degrees. The same angles measured from the membranous labyrinth were 90.12 +/- 2.64, 90.18 +/- 2.75, and 91.48 +/- 6.32 degrees. Differences between the angles formed between bony and membranous canal planes were 2.11, 6.05, and 3.26 degrees in the anterior, horizontal, and posterior canal. Pairs of membranous canal planes were nearly perpendicular without exception, but pairs of osseous canal planes had a larger deviation from 90 degrees. This suggested that membranous canals could successfully be constructed in adequate alignment for canal function in the large perilymphatic space within osseous semicircular canals.     

Vertical nystagmus provoked by locally applied calorization at the vertical semicircular canals: a study in pigeons

Calorization of the vertical semicircular canals in pigeons was performed by irrigation of water through a polyethylene cannula, that was attached at a selected site to the bony wall of the anterior or posterior canal of the labyrinth. The temperature differences between the stimulated site and the corresponding location inside the contralateral mastoid were detected by two thermistors. (a) Calorization of an anterior or posterior canal evoked a dissociated vertical nystagmus in both eyes. (b) The direction of the nystagmus and of the vertical slow phase velocity proved to be temperature-dependent. (c) The vertical eye movements disappeared when the stimulated canal was placed horizontally during calorization. (d) During parabolic flight the vertical and horizontal eye movements, elicited by sustained calorization, disappeared during short periods of microgravity and proved to be dependent to the g load. (e) All vertical canal calorizations evoked eye movements in the plane parallel to the stimulated canal. Left and right eye moved in opposite vertical directions, depending on the selected site of calorization on the vertical canal. (f) The same mode (warm or cold) of calorization of an anterior canal provoked similar vertical movements of both eyes as compared to the vertical eye movements that were induced by calorization of the contralateral posterior canal. The results are discussed in view of the 'convection current' and the 'expansion/contraction' theory and they are compared to previously reported results of vestibular nerve stimulation.     

中耳手术中的面神经定位

目的结合颞骨解剖和面神经手术，明确适用于手术的面神经解剖标志。方法44具颞骨标本面神经解剖，106例周围性面神经麻痹的面神经减压手术。根据面神经周围的固定解剖标志，确定面神经位置。结果①面神经垂直段标志：水平半规管后中1／3交界处垂直线提示面神经后缘；砧骨短角上缘弧度延长线为面神经垂直段前缘；面神经与水平半规管基本在同一深度；②面神经水平段标志：位于砧骨短突之下；在水平半规管隆突前缘向前上呈30。行走；在匙突后方，面神经与匙突平行形成中上鼓室内侧面交界缘；经过匙突面神经向前上行走到膝状神经节；③膝状神经节定位：从镫骨头到匙突等距离延长线为膝状神经节位置；④鼓索神经定位：鼓索从左侧鼓沟的3点或右侧鼓沟的9点出骨管，沿鼓沟向前行走于砧骨长突外侧和锤骨颈内侧；鼓索神经从面神经发出处距离茎乳孔5—8mm；鼓索位于鼓膜紧张部与松弛部交界处。所有手术所见面神经走向符合解剖所见。结论中耳乳突的固定标志是面神经定位的参照物，其中水平半规管的位置最恒定，根据参照物确定面神经位置提高了手术的安全性。     

Complex nystagmus in traumatic benign paroxysmal positional vertigo: A case study on the critical value of knowing semicircular canal excitation and inhibition patterns

A 73-year-old female presented to the emergency department with chief complaint of dizziness after sustaining a fall one month prior to dizziness onset. Although careful examination of eye movement patterns during positional testing was attempted at varying stages of her inpatient admission, her complex nystagmus patterns as a result of traumatic benign paroxysmal vertigo were difficult to manage. In particular, the nystagmus pattern from this case suggests the BPPV was variable and affecting either 1) left posterior semicircular canal (pSCC) exclusively 2) left pSCC and right anterior semicircular canal, 3) left and right pSCC canal. This case illustrates the importance of two critical details; positional testing should include observing nystagmus with fixation removed and an experienced clinician should be involved as early as possible.     

Anterior Canal benign paroxysmal positional Vertigo following surgical Management of superior canal dehiscence

Objective

Benign paroxysmal positional vertigo (BPPV) is a common post-surgical finding in patients managed for superior semicircular canal dehiscence (SSCD). The posterior semicircular canal has been reported as the involved canal in the majority of cases of post-surgical BPPV, with only two cases reported of lateral canal involvement. The objective of this report is to present a case in which an anterior semicircular canal BPPV response was identified in a patient following surgical management for SSCD.

The Age-Related Orientational Changes of Human Semicircular Canals

ObjectivesSome changes are found in the labyrinth anatomy during postnatal development. Although the spatial orientation of semicircular canals was thought to be stable after birth, we investigated the age-related orientational changes of human semicircular canals during development.MethodsWe retrospectively studied the computed tomography (CT) images of both ears of 76 subjects ranged from 1 to 70 years old. They were divided into 4 groups: group A (1–6 years), group B (7–12 years), group C (13–18 years), and group D (>18 years). The anatomical landmarks of the inner ear structures were determined from CT images. Their coordinates were imported into MATLAB software for calculating the semicircular canals orientation, angles between semicircular canal planes and the jugular bulb (JB) position. Differences between age groups were analyzed using multivariate statistics. Relationships between variables were analyzed using Pearson analysis.ResultsThe angle between the anterior semicircular canal plane and the coronal plane, and the angle between the horizontal semicircular canal plane and the coronal plane were smaller in group D than those in group A (P<0.05). The JB position, especially the anteroposterior position of right JB, correlated to the semicircular canals orientation (P<0.05). However, no statistically significant differences in the angles between ipsilateral canal planes among different age groups were found.ConclusionThe semicircular canals had tendencies to tilt anteriorly simultaneously as a whole with age. The JB position correlated to the spatial arrangement of semicircular canals, especially the right JB. Our calculation method helps detect developmental and pathological changes in vestibular anatomy.     

Benign paroxysmal positional vertigo in mountain bikers

We evaluated 4 men who had benign paroxysmal positional vertigo (BPPV) that occured several hours after intensive mountain biking but without head trauma. The positional maneuvers in the planes of the posterior and horizontal canals elicited BPPV, as well as transitory nystagmus. This was attributed to both the posterior and horizontal semicircular canals (SCCs) on the left side in 1 patient, in these 2 SCCs on the right side in another patient, and to the right posterior SCC in the other 2 patients. The symptoms disappeared after physiotherapeutic maneuvers in 2 patients and spontaneously in the other 2 patients. Cross-country or downhill mountain biking generates frequent vibratory impacts, which are only partially filtered through the suspension fork and the upper parts of the body. Biomechanically, during a moderate jump, before landing, the head is subjected to an acceleration close to negative 1 g, and during impact it is subjected to an upward acceleration of more than 2g. Repeated acceleration-deceleration events during intensive off-road biking might generate displacement and/or dislocation of otoconia from the otolithic organs, inducing the typical symptoms of BPPV. This new cause of posttraumatic BPPV should be considered as an injury of minor severity attributed to the practice of mountain biking.     

Posterior semicircular canal type benign paroxysmal positioning vertigo with ageotropic paroxysmal positioning nystagmus

We report on 3 patients with typical benign paroxysmal positioning vertigo (BPPV) and atypical, paroxysmal positioning nystagmus. When the Dix-Hallpike test was performed, the patients exhibited an ageotropic nystagmus, different from that classically described in posterior semicircular canal BPPV. It was torsional-vertical with the vertical component beating downwards, and the torsional component was beating away from the lowermost ear. In both left and right Dix-Hallpike positions, the upper poles of the eyes were turning away from the lowermost ear. The atypical ageotropic paroxysmal positional nystagmus of the posterior semicircular canal was observed in the evolution of the BPPV in 2 patients and on the first examination in the third. Two patients had changing patterns of paroxysmal positioning nystagmus.     

与乙状窦相关的螺旋CT影像三维定量测量

目的 为岩骨后人路手术及手术中准确定位与乙状窦相关结构提供影像解剖依据,减少手术并发症的发生.方法 收集2007年10月至2008年10月在辽宁医学院第一附属医院行螺旋CT颅底三维重建而无颅底疾病的成年人数据资料119例(238侧),其中男80例(160侧),女39例(78侧);年龄19-69岁.在ADW4.2重建工作站上利用多平面重建技术重建出轴位和冠状位图像,通过旋转显示出所要测量的解剖结构.定量测量与乙状窦相关的解剖结构间的距离,分析性别和侧别等因素对结果的影响以及各测量结果之间的关系,并将测量结果与文献中的尸头标本和干性颅骨标本上测量的数据对比,进行统计学分析.结果 解剖结构间螺旋CT影像的定量测量以(x)±s(以下同)表示,乙状窦沟宽(11.14±2.13)mm,乙状窦沟深(6.04±1.67)mill,乙状窦沟底至乳突外表面的距离(9.74±2.95)mm,乙状窦沟前缘至外耳道后壁的距离(12.98±2.71)mm,后半规管最后部至乙状窦沟前缘的距离(9.87±2.60)mm,后半规管最后部至岩骨后壁的距离(3.18±1.30)mm,外半规管长轴后端至岩骨后壁的距离(5.46±1.38)mill,外半规管长轴后端至乙状窦沟前缘的距离(13.17±2.59)mm,外半规管至颈静脉球窝顶垂直距离(6.69±3.08)mm,面神经垂直段至颈静脉窝最短距离(5.32±2.13)mm.CT测量结果与文献中尸头标本和干性颅骨标本上测量的数据比较,无明显差异.乙状窦沟前缘至外耳道后壁的距离与外半规管至颈静脉球窝顶的垂直距离、面神经垂直段至颈静脉球窝最短距离、乙状窦沟底至乳突外表面的距离呈现出正相关趋势(r值分别为0.284、0.145、0.208,P值均<0.05).结论 利用多平面重建,多排螺旋CT定量测量的结果可以代表实际的相关解剖结构间的距离;重建图像能准确显示颞骨的解剖特征和变异,从而为手术入路的选择及术中准确定位有关结构提供依据.乙状窦前置时,乙状窦更易发生外移,面神经垂直段至颈静脉球距离更短;乙状窦前置的程度与颈静脉球的高度呈正相关趋势.     

Semicircular canal orientation in the adult resting rabbit

Photographs of rabbits in the alert resting position were used to record head position. Semicircular canals were surgically exposed and points measured along each canal were used to compute the best-fit plane using a least-squares method. Computations of mean best-fit planes showed that the horizontal canals were not carried horizontally in the rabbit. The anteromedial edges were superior by 16 degrees. The anterior canals were vertically oriented and made an angle of 43 degrees to the sagittal plane. The posterior canal was tipped in the anterior direction slightly and also made an acute angle (26 degrees) with the frontal plane. Rabbit semicircular canals deviated significantly from orthogonality. The range was 86 degrees (anterior canals) to 133 degrees (posterior canals). Thus, there were no co-planar canals. Such semicircular canal geometry has implications for the neural circuitry controlling posture in the rabbit.     

A study of middle cranial fossa anatomy and anatomic variations

We conducted a study to establish standardized measurements of the common anatomic landmarks used during surgery via the middle cranial fossa approach. Results were based on high-resolution computed tomography (CT) images of 98 temporal bones in 54 consecutively presenting patients. Measurements were obtained with the assistance of the standard PACS (picture archiving and communication system) software. We found that the superior semicircular canal (SSC) dome was not the highest point on the temporal bone (i.e., the arcuate eminence) in 78 of the temporal bone images (79.6%). Pneumatization above the SSC and above the internal auditory canal (IAC) was found in 27 (27.6%) and 39 (39.8%) temporal bone images, respectively. The anterior wall of the external auditory canal was always anterior to the anterior wall of the IAC. The mean angles between the SSC and the posterior and anterior walls of the IAC were 42.3 degrees and 60.8 degrees, respectively. We also measured other distances, and we compared our findings with those published by others. We hope that the results of our study will help surgeons safely and rapidly locate anatomic landmarks when performing surgery via the middle cranial fossa approach.     

Changes in the perceived head transversal plane and the subjective visual horizontal induced by Coriolis stimulation during gondola centrifugation

For studying the influence of the vertical semicircular canals on spatial orientation in roll, the subjective visual horizontal (SVH) and the subjective transversal plane of the head (STP) were measured in a situation where the vertical canals sense a roll-velocity stimulus while the otolith organs persistently signal that the head is upright in roll. During gondola centrifugation (resultant gravitoinertial force vector 2.5 G, gondola inclination 66 degrees) subjects were exposed to controlled rotational head movements (angular speed 27 degrees/s, magnitude 40 degrees) about the yaw (body z-) axis, produced by means of a motor-driven helmet. This causes a roll-plane Coriolis stimulus to the canals, while the otoliths persistently sense upright head position in roll. The subjects reported intense sensations of rotation and tilt in the roll plane. This was reflected in tilts of both the SVH and STP. The initial tilt of the SVH was 13.0 +/- 9.7 degrees (mean +/- S.D., n=10). The STP was changed in the opposite direction. The initial tilt was 23.8 +/- 12.2 degrees (mean +/- S.D., n=5). The changes in the SVH and STP were not of equal magnitude. A few subjects who had almost no deviations in the SVH showed pronounced tilts of the STP. The time constant for exponential decay of the tilts of the SVH and STP was on average approximately 1 minute. These findings indicate that a difference in activity of the vertical canals in the right versus left ear may cause substantial tilts of the SVH even if there is no asymmetry in the activity of the otolith system. Further, the canal stimulus may induce a tilt of the fundamental egocentric frame of reference.     

Cristospinal reflex in circular walking.

This study comprised 22 normal adults, 12 males and 10 females. Electromyograms of the bilateral gastrocnemius muscle were recorded during circular walking under two conditions: no caloric stimulation and immediately after irrigating the right auditory canal with 20 degrees C water for 20 s with the horizontal semicircular canal maintained in vertical position. With no caloric stimulation, gastrocnemius muscle activity on the right side exceeded that on the left during dextrorotation and vice versa during sinistrorotation. Following irrigation of the right auditory canal, the activity was greater on the left side than on the right during sinistrorotation, but no consistent differences in muscle activity were observed during dextrorotation. Dextrorotation was associated with ataxic gait in all cases. Thus ampullopetal lymphatic flow in the semicircular canal due to circular walking causes increased antigravity muscle tonus of the ipsilateral leg. This gives the ipsilateral leg assistance for supporting body weight which shifts to the inner side of circular walking.