The vestibular and non vestibular components of the caloric vestibular stimulus – a positron emission tomography study
Abstract
There are different stimulation methods for investigation of the vestibular system. In addition to optokinetic, galvanic and neck vibration tests the most wide-spread is the caloric stimulation. These listed methods cause not only vestibular but other different effects on the central nervous system (CNS) (acustic, tactile and nociceptive). The authors using positron emission tomograhy (PET) investigated, whether the caloric stimulation contains some part of non vestibular (extravestibular) component by causing distortion of vestibular effect on CNS. Via caloric test was investigated six patient operated because of cerebello-pontin angle tumor. Postoperatively the patients suffered from complete lesion of vestibular system and anacusis on the side of operation. It was measured the increasing and decreasing of regional cerebral blood flow (rCBF) caused by vestibular stimulation on the operated side. Ipsilaterally activated areas were: inferior pole of postcentral gyrus and temporoparietal junction, the caudal part of postcentral gyrus (S I, S II), inferior parietal lobule and medial frontal gyrus. Contralaterally activated areas were: anterior cingulate gyrus, medial frontal gyrus, posterior part of insula, postcentral gyrus, temporoparietal junction (S II). Ipsilaterally deactivated areas were: caudal and cranial part of medial occipital gyrus (V 2, V 3, V 4, V 5). Contralaterally deactivated areas were: lingual gyrus and inferior occipital gyrus (V 2, V 3) and fusiform gyrus. On the base of these dates it was postulated that during caloric stimulation rising extravestibular reaction too. It is correspond to the subjective feeling of heat and pain. The authors demonstrated the deactivation of occipital cortex caused by extravestibular effect. This is the first time suggestion of possibility of the nociceptive-visual interaction.
