Changes in brain activation caused by caloric stimulation in the case of cochleovestibular denervation--PET study.

There are a number of well-known stimulation methods for the investigation of the central projection of the vestibular system. In addition to optokinetic, galvanic and neck vibration tests, the most widespread method is caloric stimulation. These listed methods cause not only vestibular, but also other effects on the central nervous system (CNS) (acoustic, tactile and nociceptive). In this paper, positron emission tomography (PET) was used to investigate whether caloric stimulation contains a non-vestibular (extravestibular) component, which would cause a distortion in the cortical activity and therefore in the vestibular effect on the CNS. Caloric stimulation was carried out in six patients who had been operated on due to cerebello-pontine angle tumour. These patients suffered post-operatively from a complete lesion of the vestibular system and anacusis on the operated side. Ipsilaterally activated areas were the inferior pole of the post-central gyrus and temporoparietal junction, caudal part of the post-central gyrus (SI, SII), inferior parietal lobule and medial frontal gyrus. Contralaterally activated areas were the anterior cingulate gyrus, medial frontal gyrus, posterior part of the insula, post-central gyrus and temporoparietal junction (SII). Ipsilaterally deactivated areas were the caudal and cranial part of the medial occipital gyrus (V2, V3, V4, V5). Contralaterally deactivated areas were the lingual gyrus, inferior occipital gyrus (V2, V3) and fusiform gyrus. On the basis of these data, it was postulated that, during caloric stimulation, extravestibular reaction also occurs, which corresponds to the subjective feeling of heat and pain. The deactivation of the occipital cortex due to an extravestibular effect was demonstrated. This is the first observation to suggest the possibility of nociceptivevisual interaction.

[Processing vestibular impulses in the central nervous system. Study based on positron emission tomography]. / Verarbeitung vestibulärer Impulse im Zentralnervensystem. Untersuchung anhand der Positronen-Emissions-Tomographie.

BACKGROUND AND OBJECTIVE: Functional imaging methods have opened new perspectives for vestibular research. Many authors have investigated the central connections of the system, but the differences between the reports leave further questions open. We investigated the cerebral projection of the vestibular system, using positron emission tomography in right-handed subjects. PATIENTS AND METHODS: Bilateral caloric stimulation was used in every volunteer (n = 6). This can be considered a standard method, which will make it possible to compare the results from different laboratories in the future. A detailed map of activated and deactivated brain regions is included. RESULTS: Changes caused by vestibular stimulation are portrayed. The activated regions partially correspond with previous results in the literature. We would like to point out the Brodmann 6 region as the cortical manifestation of involuntary isometric tightening of muscles. We have found many, previously unidentified regions showing decreased regional cerebral blood flow. CONCLUSIONS: We are the first to point out the functional connection between the hippocampus and the vestibular system in this report.

[Investigation of the cerebral projection of the vestibular system using positron emission tomography]. / A vestibularis ingerület központi idegrendszeri feldolgozásának agyaktivációs vizsgálata pozitronemissziós tomográfiával.

The authors investigated the cerebral projection of the vestibular system, using positron emission tomography, in right-handed subjects. Both sided cold caloric stimulation was used in every volunteer (n = 6). A detailed map of activated and deactivated brain regions is included. This portrays changes caused by vestibular stimulation. The contralaterally activated regions according to the stimulation side were: postcentral gyrus, transvers temporal gyrus, superior temporal gyrus, posterior part of the insula, claustrum, putamen, inferior parietal lobule, precentral gyrus, premotor cortex, cingulate gyrus. The ipsilaterally activated regions were: transvers temporal gyrus, superior temporal gyrus, inferior parietal lobule, posterior part of the insula. There was no hemispherial dominance. The activated regions partially correspond with previous results in the literature. It would like to be pointed out the Brodmann 6 region as the cortical manifestation of involuntary isometric tightening of muscles. The contralaterally deactivated regions were: inferior, superior and medius temporal gyrus, medial and medius frontal gyrus, inferior occipital gyrus, parahippocampal gyrus and hippocampus. Ipsilaterally deactivated regions were: superior and medial frontal gyrus, inferior temporal gyrus, angular gyrus, parahippocampal gyrus and hippocampus, fusiform and inferior occipital gyrus. There was prominent hemispherial dominance in the stimulated, ipsilateral side. The deactivation based functional connection between the hippocampus and the vestibular system was pointed out in such a relation for the first time in this report.

A proposal for introducing a modified vestibular index in neurotology. The classification of vestibular neuronitis.

The parameters for vestibular dysfunction were modified after our own studies. This index includes the degree of vertigo present, spontaneous nystagmus, dysfunction of the vestibulospinal reflexes and caloric and postrotatory side differences. The index is applicable for defining the extent of a lesion, follow-up, defining its stage and the results of therapy. Introduction of the modified vestibular index is proposed for use in clinical diagnosis. Classification of vestibular neuronitis into groups A, B and C is suggested on the basis of the reversibility of spontaneous nystagmus after caloric stimulation.