International journal of equilibrium research最新文献

Electrical stimulation of the utricle in C-1 transected cats (whose labyrinths remained sensitive to natural stimulation) induced bilateral pupillary dilatation and bilateral 0.4 to 3.0 diopter lens change in an anti-accommodative direction. Both effects could still be induced two weeks after cutting the ipsilateral cervical sympathetic trunk. It is concluded that these effects take place by inhibiting the parasympathetic pathway originating in the Edinger-Westphal nucleus. The mediating pathways from the vestibular complex to the Edinger-Westphal nucleus pass through the brain stem in the region outside the medial longitudinal fasciculi.

OKN and OKAN were affected by unilateral and bilateral labyrinthectomy. The maximum velocity of slow phases of OKN induced by drum rotations above 60-75 degrees/sec in either direction was lower after unilateral and bilateral labyrinthectomy. The frequency of OKN was also decreased, and the total deviation of the eyes was reduced for OKN induced by these drum speeds. Changes in OKN eventually recovered. OKAN was reduced in duration after unilateral labyrinthectomy, being initially shorter to the ipsilateral than to the contralateral side. OKAN could no longer be evoked after bilateral labyrinthectomy. This loss was permanent. These data demonstrate the importance of the vestibular system in maintenance of OKN and OKAN.

Diagnostic considerations based upon the nystagmogram are limited. Quantitative assessment of horizontal canal sensitivity is available through the use of culmination frequency or culmination slow phase velocity. Qualitative characteristics of nystagmometry have been sought but with no satisfactory results. Three distinctive features of the caloric nystagmus were evaluated and were found to be suggestive or outrightly pathognomonic for retrolabyrinthine or central nervous system abnormalities. These are: (1) Vestibular decruitment. The disproportionate caloric responsiveness when a weak stimulus elicits a more intense nystagmic reaction than a strong stimulus is capable of creating. (2) Hyperactive vestibular responsiveness (3) Ocular fixation reversal phenomenon. Contrary to the normal behaviour, the elimination of fixation decreases the nystagmus intensity instead of facilitating the evoked nystagmus. The assessment of these qualitative features of the caloric nystagmus in addition to the quantitative measurements widens the scope of our diagnostic capabilities.

An experiment was designed to investigate the effect of different modes of vestibular habituation. Volunteers were divided into two groups differing only in visual fixation. A theoretical explanation of the observed differences in nystagmus speed and frequency of beats between groups is offered. Secondary experiments designed to support the conclusions were performed using optokinetic stimulation with a stationary line for visual fixation. An increase in conjugate tone potential opposed to the unwanted optokinetic stimulus developed. Post-habituation nystagmus patterns appear to depend in considerable part on learned responses originating in the gray matter of the brain.

Comparative examinations made on patients suffering of a degenerative disease of the retina causing a loss of their macular or their peripheral vision respectively and on patients with a lesion of the frontal or occipital lobe have revealed that the optokinetic nystagmus of patients with a frontal lesion behaves similar to the one elicited in patients with macular pathology, whereas the optokinetic nystagmus of patients with a lesion of the occipital eye fields revealed similar characteristics as the one evoked in patients with tubular field.