32 research outputs found
Vestibular evoked myogenic potential: recording methods in humans and guinea pigs
O potencial miogĂȘnico evocado vestibular (VEMP) Ă© um teste clĂnico que avalia a função vestibular atravĂ©s de um reflexo vestĂbulo-cervical inibitĂłrio captado nos mĂșsculos do corpo em resposta Ă estimulação acĂșstica de alta intensidade.
OBJETIVO: Verificar e analisar os diversos mĂ©todos de registro dos potenciais miogĂȘnicos evocados vestibulares no homem e em cobaias.
MATERIAL E MĂTODO: Realizou-se busca eletrĂŽnica nas bases de dados MEDLINE, LILACS, SCIELO e COCHRANE.
RESULTADOS: Foram verificadas divergĂȘncias quanto Ă s formas de registro dos potenciais miogĂȘnicos evocados vestibulares, relacionadas com os seguintes fatores: posição do paciente no momento do registro, tipo de estĂmulo sonoro utilizado (clicks ou tone bursts), parĂąmetros para a promediação dos estĂmulos (intensidade, freqĂŒĂȘncia, tempo de apresentação, filtros, ganho de amplificação das respostas e janelas para captação dos estĂmulos), tipo de fone utilizado e forma de apresentação dos estĂmulos (monoaural ou binaural, ipsi ou contralateral).
CONCLUSĂO: NĂŁo existe consenso na literatura quanto ao melhor mĂ©todo de registro dos potenciais evocados miogĂȘnicos vestibulares, havendo necessidade de pesquisas mais especĂficas para comparação entre estes registros e a definição de um modelo padrĂŁo para a utilização na prĂĄtica clĂnica
Bilateral Dorsal Cochlear Nucleus Lesions Prevent Acoustic-Trauma Induced Tinnitus in an Animal Model
Animal experiments suggest that chronic tinnitus (âringing in the earsâ) may result from processes that overcompensate for lost afferent input. Abnormally elevated spontaneous neural activity has been found in the dorsal cochlear nucleus (DCN) of animals with psychophysical evidence of tinnitus. However, it has also been reported that DCN ablation fails to reduce established tinnitus. Since other auditory areas have been implicated in tinnitus, the role of the DCN is unresolved. The apparently conflicting electrophysiological and lesion data can be reconciled if the DCN serves as a necessary trigger zone rather than a chronic generator of tinnitus. The present experiment used lesion procedures identical to those that failed to decrease pre-existing tinnitus. The exception was that lesions were done prior to tinnitus induction. Young adult rats were trained and tested using a psychophysical procedure shown to detect tinnitus. Tinnitus was induced by a single unilateral high-level noise exposure. Consistent with the trigger hypothesis, bilateral dorsal DCN lesions made before high-level noise exposure prevented the development of tinnitus. A protective effect stemming from disruption of the afferent pathway could not explain the outcome because unilateral lesions ipsilateral to the noise exposure did not prevent tinnitus and unilateral lesions contralateral to the noise exposure actually exacerbated the tinnitus. The DCN trigger mechanism may involve plastic circuits that, through loss of inhibition, or upregulation of excitation, increase spontaneous neural output to rostral areas such as the inferior colliculus. The increased drive could produce persistent pathological changes in the rostral areas, such as high-frequency bursting and decreased interspike variance, that comprise the chronic tinnitus signal