Journal of Vestibular Research - Volume 9, issue 5

Authors: McCollum, Gin

Article Type: Research Article

Abstract: The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control …structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for postural adjustments for healthy subjects and certain types of vestibular patients. The sensorimotor control structures for patients with absent vestibular function suggest implications for management of the deficit. Show more

Keywords: control, mathematical, sensorimotor, vestibular

DOI: 10.3233/VES-1999-9501

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 303-325, 1999

Authors: Li, M.W. | Houlden, D. | Tomlinson, R.D.

Article Type: Research Article

Abstract: Recordings were obtained from a total of 25 normal subjects of the electromyographic (EMG) responses in the sternocleidomastoid muscle (SCM) to intense sound stimuli. While previous authors have demonstrated these responses exist, it has remained unclear whether the EMG response is unilateral or bilateral in nature. Accordingly, we chose a remote site, linked-wrists, for our reference electrodes so that we could be certain that no significant volume conduction of potentials could occur from the source in the SCM to the reference site. When this was done we found that if the sternum was used as a reference site, as was …the case in previous studies, some subjects exhibited bilateral responses while in others, the response was ipsilateral. However, with linked-wrists as the reference site, responses were always purely ipsilateral. Furthermore, recordings that used the sternum or the ipsilateral mastoid process as active sites and linked-wrists as a reference, exhibited responses which were inverted. Thus, both the sternum and the ipsilateral mastoid process are electrically active due to volume conduction from the nearby source in the SCM. The ambiguity in previous recordings can be attributed to the use of these active sites as a reference. When SCM responses are recorded versus a remote, electrically inactive site, the responses are purely ipsilateral. Show more

Keywords: vestibular, saccule, sound, laterality

DOI: 10.3233/VES-1999-9502

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 327-334, 1999

Authors: Zheng, Yiwen | Smith, Paul F. | Darlington, Cynthia L.

Article Type: Research Article

Abstract: Recent behavioural and neurophysiological studies suggest that the hippocampus uses vestibular information, along with information from other sensory systems, to accomplish its spatial computational processing. By contrast, there is a dearth of neurochemical data on the interactions between the vestibular system and hippocampus. The aim of the present study was to examine levels of glutamine, glutamate, gamma-amino-butyric acid (GABA), glycine, serine, threonine and taurine in the CA1, CA2, CA3 and dentate gyrus (DG) subregions of the hippocampus at 10 hs following UVD in guinea pig, using high-performance liquid chromatography (HPLC) with electrochemical detection (ECD). Glutamine levels were not significantly different …between the UVD and control conditions, except in the bilateral DG where they were significantly lower (p < 0.05 ). However, no significant differences in glutamate levels were observed. Although there were no significant differences in GABA levels in the DG, CA1 and CA2 regions following UVD, there was a significant increase in GABA levels in the contralateral CA3 region in the sham group compared to intact anesthetic controls. Glycine levels were significantly higher in the contralateral DG and ipsilateral CA1 in the sham groups compared to intact anesthetic controls (p < 0.05 ). However, in contralateral CA2 and ipsilateral CA3, glycine levels were significantly higher for both the sham and UVD groups compared to anesthetic controls (p < 0.05 ). Threonine levels were not significantly different in CA1; however, in ipsilateral DG and ipsilateral CA3, they were significantly higher in the sham groups compared to anesthetic controls and the UVD groups (p < 0.05 ). In ipsilateral CA2, threonine levels were significantly higher in the UVD group compared to anesthetic controls (p < 0.05 ). Taurine levels did not differ significantly in the DG, CA1 or CA3 following UVD; however, they were significantly higher in ipsilateral CA2 following UVD (p < 0.05 ). Finally, serine levels were not significantly different in any area of the hippocampus following UVD or sham surgery. This study provides the first data on amino acid levels in the hippocampus following UVD and sham temporal bone surgery and suggests that peripheral vestibular damage may particularly affect glutamine, glycine, threonine and taurine levels in various subregions of the hippocampus. Show more

Keywords: amino acids, hippocampus, vestibular compensation, glutamate, glutamine, GABA, glycine, threonine, taurine, serine

DOI: 10.3233/VES-1999-9503

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 335-345, 1999

Authors: Tribukait, A.

Article Type: Research Article

Abstract: Measurements of the subjective visual horizontal (SVH) were performed in 11 healthy test persons during an increase of the resultant gravitoinertial force vector in a large swing-out gondola centrifuge. Three levels of hypergravity (1.5g, 2.0g, 2.5g) were used, each with a duration of 4 minutes and with 1–2 minute pauses at 1.0g in between. The direction of the resultant gravitoinertial force vector was always parallel with the head and body length axis. Hence, there was no roll stimulus to the otolith organs. The swing-out of the gondola during acceleration, however, is sensed by the vertical semicircular canals as a change …in roll head position, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge there was a tilt of the SVH relative to the resultant gravitoinertial horizontal. This tilt gradually decayed during the 4-minute period of recordings. For a subgroup of seven test subjects who had completely normal ENG-recordings in 1g environment, the initial offset of SVH and the time constants for exponential decay were determined for each g level; initial offsets: 9 . 9 ∘ (1.5g), 7 . 7 ∘ (2.0g), 6 . 1 ∘ (2.5g); time constants: 89s (1.5g), 74s (2.0g), 37s (2.5g). The offset of SVH is interpreted as being the result of mainly the stimulus to the vertical semicircular canals during acceleration of the centrifuge. The slow decay, however, does not correspond to the dynamics of the semicircular canal system, and is suggested to reflect some kind of central position storage mechanism. A smaller offset and more rapid decay for the higher g loads may be explained by an increasing dominance of graviceptive input, presumably from the saccules. In conclusion, these results might suggest the role of the vertical semicircular canals as well as the sacculus in the formation of SVH. They may also have relevance with regard to the spatial disorientation problem in aviators. Show more

Keywords: vestibular system, spatial orientation, subjective visual horizontal, hypergravity

DOI: 10.3233/VES-1999-9504

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 347-357, 1999

Authors: Lustig, Lawrence R. | Hiel, Hakim | Fuchs, Paul A.

Article Type: Research Article

Abstract: The efferent cholinergic pathways to the vestibular periphery have yet to be fully characterized. While the nicotinic acetylcholine receptor subunit (nAChR) α 9 is now regarded as the principle receptor for efferent cholinergic signaling to the organ of Corti, there is still uncertainty over how the more complex efferent effects of the labyrinth are produced. Recent experimental work has demonstrated that the nAChR α 9 is present in the vestibular end-organs of the rat and mouse, suggesting that α 9 may be one of the mediators of efferent cholinergic signaling in the vestibular periphery as well. In this experiment, we …sought to determine whether α 9 was also present in the vestibular end-organs of the chick. A homologue of α 9 has been cloned recently from the chick cochlea. Using reverse transcription polymerase chain reaction (RT-PCR), individual vestibular end-organ preparations, including posterior ampulla, combined horizontal and superior ampulla, saccule, utricle, and the vestibular ganglion were screened for α 9 messenger RNA expression. In each end-organ and the vestibular ganglion, a cDNA of the expected size was obtained by RT-PCR and was confirmed to be α 9 by sequence analysis. Further, α 9 mRNA was identified by RT-PCR from individually isolated type I and type II vestibular hair cells (single-cell RT-PCR). Lastly, insitu hybridization using digoxigenin-labeled α 9 riboprobes confirmed the presence of α 9 in type I and type II hair cells throughout the vestibular periphery. These results demonstrate the expression of α 9 in the vestibular end-organs of the chick, and lend further support for the role of α 9 as a mediator of efferent cholinergic signaling in vestibular hair cells. Show more

DOI: 10.3233/VES-1999-9505

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 359-367, 1999

Authors: Black, F. Owen | Paloski, William H. | Reschke, Millard F. | Igarashi, Makoto | Guedry, Fred | Anderson, David J.

Article Type: Research Article

Abstract: Postural instability (relative to pre-flight) has been observed in all shuttle astronauts studied upon return from orbital missions. Postural stability was more closely examined in four shuttle astronaut subjects before and after an 8 day orbital mission. Results of the pre- and post- flight postural stability studies were compared with a larger (n = 34 ) study of astronauts returning from shuttle missions of similar duration. Results from both studies indicated that inadequate vestibular feedback was the most significant sensory deficit contributing to the postural instability observed post flight. For two of the four IML-1 astronauts, post-flight postural …instability and rate of recovery toward their earth-normal performance matched the performance of the larger sample. However, post-flight postural control in one returning astronaut was substantially below mean performance. This individual, who was within normal limits with respect to postural control before the mission, indicated that recovery to pre-flight postural stability was also interrupted by a post-flight pitch plane rotation test. A similar, though less extreme departure from the mean recovery trajectory was present in another astronaut following the same post-flight rotation test. The pitch plane rotation stimuli included otolith stimuli in the form of both transient tangential and constant centripetal linear acceleration components. We inferred from these findings that adaptation on orbit and re-adaptation on earth involved a change in sensorimotor integration of vestibular signals most likely from the otolith organs. Show more

Keywords: orbital space flight, postural instability, space adaptation syndrome, otolith control of posture, countermeasures

DOI: 10.3233/VES-1999-9506

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 369-378, 1999

Authors: Paquet, Nicole | Hui-Chan, Christina W.Y.

Article Type: Research Article

Abstract: The modulation of soleus (SO) H-reflex excitability during dynamic whole head-and-body tilts (WHBT) was investigated in normal healthy subjects. Between 30 and 70 ms, and 151 and 190 ms after head acceleration onset, the H-reflex amplitude was smaller than during quiet standing by 7.6% (p < 0.01 ) and 15.4% (p = 0.06 ) respectively. This finding suggested that dynamic WHBT reduced the excitability of the predominantly monosynaptic stretch reflex arc in the majority of the subjects studied.

Keywords: H-reflex, head-and-body tilt, balance control, human

DOI: 10.3233/VES-1999-9507

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 379-383, 1999

Authors: Fetter, Michael

Article Type: Book Review

DOI: 10.3233/VES-1999-9508

Citation: Journal of Vestibular Research, vol. 9, no. 5, pp. 385-385, 1999