To demonstrate the neural mechanisms underlying the vestibulocollic reflex, we analyzed input patterns from six semicircular canals to motoneurons of various neck muscles in the cat. Stimulating electrodes were implanted on six canal nerves according to the method developed by Suzuki et al (1964). Intracellular potentials were recorded in neck motoneurons, when individual canal nerves were separately stimulated. We analyzed the patterns of postsynaptic potentials in neck motoneurons evoked by stimulation of individual canal nerves, and determined the pathways conveying these effects by making lesions in the brainstem. Input patterns from six semicircular canals to motoneurons of 16 different neck muscles were classified into four groups according to input patterns from the vertical canals, since input patterns from the lateral canals were common in all neck motoneurons. Classification of neck muscles based on comparative anatomy and phylogenetic myology was well correlated to classification of neck muscles based on the above input patterns from the semicircular canals.
The central nervous system (CNS) processes information mapped on a large number of different coordinate systems. In case of goal-directed movements such as orienting and forearm reaching, the spatial location of the target perceived via various sensory modalities are mapped onto a common flame of spatial coordinates. To execute movements toward the target, information about its location, mapped on such spatial coordinates is transformed into the spatial and temporal pattern of activation of many skeletal muscles, mapped on the body coordinate system. Such coordinate transformation includes ill-posed problem, since the dimension of the body coordinates is usually much larger than that of the spatial coordinates. To overcome such problems, the CNS should involve some neural constraint. In case of orienting head movements, the spatial information mapped on the superior colliculus (SC) is processed by the interneuronal system in the brainstem reticular formation and drives neck motoneurons. The brainstem interneuronal systems are largely divided into two major groups, one in the medial pontine reticular formation and the other in the mesodiencephalic junction. The former neurons control the horizontal component of head movements and the muscle synergies for it, while the latter control the vertical component and the muscle synergy for it. Such "intermediate coordinate system" may serve as the neural constraint resolving the ill-posed problem. The above described neural constraint for the coordinate transformation is one of the major issues related to coordinate processing in the brain. However, mapping of information in various sensory modalities onto the common flame of spatial coordinates and calibration of these different coordinates is another important issue. The SC is a key structure of such common frame of spatial coordinates. Several studies showed that in the case of the SC, visual input guides the spatial map of other modalities such as the auditory system to the common frame of the spatial map.
Lateral linear acceleration induces otolithic nystagmus and the otolith-ocular reflex (OOR). These response properties have been studied mostly by dynamic analysis using sinusoidal translation, and only a few reports are available so far with static analysis using step-mode acceleration, due to technical limitations. According to our studies using a linear accelerator with a period up to several seconds of step-mode lateral oscillation (Mori and Katayama, 1998; Katayama and Mori 2001), the direction of nystagmus is dependent on G-direction and directional preponderance (DP) of nystagmus elicitation is physiological. The slow cumulative eye-position (SCEP) curve in which the fast components are eliminated is saw-toothed in shape when lateral oscillation continues in a step mode, implying that the eye position, instead of the eye velocity, is controlled by stimulus velocity signals. The SCEP often accompanies a slow drift during the oscillation, and the slow-drift slope is positively correlated with DP: the steeper the slope, the larger the DP. The OOR velocity measured from the SCEP slope is symmetrical between G-directions when the slow drift is cancelled algebraically. Such symmetry in OOR velocity is in agreement with the previous reports (Gianna et al., 1997; Lempert et al., 1998 1999) using a short and single step-mode acceleration, suggesting that the slow drift is a component hidden behind the ordinary ocular movement and adjusted by the fast phase of nystagmus.
This study examined the interrelationships between various parameters evaluating body sway from the center of foot pressure (CFP) during a static standing posture, and gender difference by domain. The subjects were 220 healthy young males and females. CFP was measured 3 times with a 1 min rest, and the mean of trials 2 and 3 was used for the analysis. The measurement device was Anima's stabilometer G-5500. Data sampling frequency was 20Hz. Sixty parameters with higher reliability were selected from the following 7 domains: distance, center average, distribution of amplitude, area, velocity, power spectrum, and body sway vector. Several parameters showed a significant gender difference, but the degree was not large. The correlation coefficients between parameters in each domain of distance, center average, distribution of amplitude, area, velocity, and body sway vector were very high, and they tended to relate closely to some parameters in the other domains. Gender difference in the correlation coefficient was insignificant. Therefore, the relationship between parameters in both genders was judged to be very similar. After examining the interrelationship between parameters, 36 parameters were selected. We judged that the body sway can be synthetically evaluated by these rather than 60 parameters.
Vestibular-evoked-myogenic-potentials (VEMP) have been considered to reflect the function of saccular and inferior vestibular nerve tracts. We encountered a patient with inferior vestibular schwannoma who showed severely damaged hearing, with normal caloric tests and VEMP results. A 54-year-old woman with no contributing history or family history consulted with a complaint of hearing loss and tinnitus. On brain MRI, she was found to have an acoustic tumor in her right internal auditory meatus, about 8mm in diameter. Audiometry results showed severe hearing loss, 106.3 dB in right ear. Caloric test and VEMP result showed normal responses. The tumor was considered to originate from the cochlear nerve, but operation revealed an inferior vestibular schwannoma origin. After schwannoma enucleation with section of inferior vestibular nerve, VEMP results showed no response, confirming VEMP may be conducted by the inferior vestibular nerve, and showing that it is difficult to estimate neuron origin from preoperative caloric tests and VEMP results. In addition, it showed that VEMP may be conducted via the cochlear nerve as well as in the inferior vestibular nerve. Thus, evaluation of inferior vestibular nerve function should be performed carefully. Additional accumulation of cases and data are necessary for better understanding.
We developed a new evaluation method for the Body Tracking Test (BTT), which evaluates dynamic body balance functions. The evaluation method conventionally used in BTT is called the 5-grade evaluation of tracking ability, in which the score is divided into 5 grades, from A to E. According to this method, the score is based on how frequently movement of the optical target of BTT is in phase with movement of the subject's center of gravity. As this method is marred by the problem of subjective evaluation, we developed a new objective and quantitative evaluation method. We formulated this new evaluation method based on the approach of the 5-grade evaluation of tracking ability. According to this new evaluation method, evaluation is based on the following steps. First, define equal-interval widths from the axis of the optical target's movement in the vertical direction as the evaluation widths. Then, draw a straight line parallel to the optical target's movement using the evaluation width, and perform an evaluation based on the number of samples of tracked trajectories that are enclosed by this line. We also developed a method called the 10-grade evaluation of tracking ability based on such an evaluation method. The 10-grade evaluations of tracking ability enabled objective and detailed evaluation classifications.