Anatomía, fisiología y rol clínico de la corteza vestibular / Anatomy, physiology and clinical role of the vestibular cortex

El sistema vestibular, mediante sus órganos periféricos, nos permite procesar correctamente los cambios de aceleración angular de la cabeza y lineal del cuerpo y así permitirnos una correcta orientación en el espacio. Esta información sensorial es dirigida hacia los núcleos vestibulares y desde aquí se comunica con los núcleos óculo-motores y estructuras del tálamo a través de tractos ascendentes del tronco encefálico. Posteriormente la información se dirige hacia centros subcorticales y corticales de naturaleza eminentemente multisensorial. La naturaleza y función de estas estructuras es controversial. En esta revisión se abordan los principales conceptos y descubrimientos a nivel de investigación básica y clínica del procesamiento cortical generado por estimulación de tipo vestibular.

The vestibular system, thanks to its peripheral organs, allows us to properly process the angular head movements and linear acceleration in order to give us a proper orientation in space. The information from these sensory inputs is routed to the vestibular nuclei and thence ascending tracts of the brainstem, which communicate with the oculomotor nuclei of the thalamus and structures. Then the information goes to subcortical and cortical centers, which are eminently multisensory nature. The nature and function of these structures are controversial. In this review the main concepts and discoveries at the level of basic and clinical research generated cortical processing of vestibular stimulation are addressed.

Comparative study between elderly fallers and non fallers based on clinical balance tests, sensory organization and limits of stability

The aim of this study is to pick up elderly people who are at risk of falling or recurrent falling and to set comparison between elderly fallers and non fallers through sensory information, functional evaluation and gait pattern. Fifty elderly subject were included in the study, subjects were divided into two groups. Non Faller [NF] and Faller [F]. We compared between NF and F in either classification as regards clinical balance tests in the form of [Three-meters Timed Up and Go test [TUG-3], Five-times Sit To Stand test [STS-5], One Leg Balance Eye Opened [OLB-EO], One Leg Balance Eye Closed [OLB-EC] and Computerized Dynamic Posturography [CDP] using Neurocom system in the form of [Sensory Organization Test [SOT], Limits Of Stability [LOS], Tandem Walk [TW] and Sit To Stand test [STS]. The result showed significant affection of sensory systems in charge of balance control [vestibular, visual, Somatosensory and Preference] for F on comparison with NF. LOS test revealed that F showed more sway and asymmetrical movement in various directions. TW test showed that F exhibited worse performance of the test attributed to the increased End sway more than NF. Computerized Dynamic Posturography [CDP] has the ability to detect changes of all balance components; sensory information, motor response and functional performance better than clinical tests and thus shows the ability to pick up elderly at risk of falling through identifying early and minimal pathological affection

Potencial evocado miogênico vestibular (Vemp): avaliação das respostas em indivíduos normais / Vestibular evoked myogenic potential (Vemp): evaluation of responses in normal subjects

TEMA: o Potencial Evocado Miogênico Vestibular (Vemp) é formado por respostas miogênicas ativadas por estimulação sonora de alta intensidade. Essas respostas são registradas por eletromiografia de superfície sobre a musculatura cervical na presença de contração muscular, ativando a mácula, o nervo vestibular inferior e as vias vestíbulo-espinhais descendentes. OBJETIVO: descrever as respostas evocadas do Vemp em uma população normal. MÉTODO: selecionaram-se 30 sujeitos adultos, sendo 13 homens e 17 mulheres, sem queixas otoneurológicas. Utilizou-se 200 estímulos tone burst com freqüência de 1Hz e intensidade de 118dB Na, filtro passa-banda de 10Hz a 1500Hz. Os traçados obtidos foram analisados em relação ao primeiro potencial bifásico composto por P13 e N23. RESULTADOS: não houve diferença estatisticamente significativa entre o lado da estimulação em relação a latência e amplitude, porém foi encontrada diferença estatisticamente significativa em relação à amplitude do potencial entre os sexos. CONCLUSÃO: Vemp demonstrou ser uma ferramenta confiável na avaliação da função vestibular.

BACKGROUND: the Vestibular Evoked Myogenic Potential (Vemp) is formed by myogenic neurophysiologic responses activated by high-intensity sound stimulation. The response is registered through surface electromyography of the cervical muscles during muscle contraction. The acoustic stimuli activate the saccular macula, the vestibular inferior nerve and the pathways related to the vestibule-spinal descendant nerves. AIM: to describe Vemp parameters in a normal population. METHODS: thirty adults, 13 men and 17 women with no otoneurological complaints were selected. The stimuli were 200 tone burst, with a frequency of 1Hz and intensity of 118 dB Na, band-pass filter ranging from 10Hz to 1500Hz. The first potential biphasic P13-N23 wave was analyzed. RESULTS: no significant difference was observed between the sides of stimulation in terms of latency and amplitude. However, a statistically significant difference was found for amplitude between genders. CONCLUSION: Vemp demonstrated to be a reliable instrument in the clinical assessment of the vestibular function.

Importancia clínica de la prueba calórica mínima / Clinical importance of the minimal caloric test

Introducción: En la evaluación de la patología vestibular habitualmente se utiliza la prueba calórica clásica de Fitzgerald y Hallpike (PCC). Sin embargo, esta sólo evalúa la función del nervio vestibular superior a través de la estimulación del canal semicircular lateral. La prueba calórica mínima (PCM) permite evaluar tanto la función del nervio vestibular superior como del nervio vestibular inferior a través de la estimulación del canal semicircular lateral y posterior respectivamente. Se desconoce el real impacto de la PCM en la evaluación clínica de pacientes con sintomatología vestibular. Objetivo: Cuantificar la utilidad diagnóstica de la PCM en pacientes con sintomatología vestibular. Material y método: Estudio diagnóstico transversal. Se obtuvo la sensibilidad y especificidad de la PCM al comparar la respuesta del canal semicircular lateral en la PCM con la prueba calórica convencional. Se evaluó en cuántos casos la información sobre la función del nervio vestibular inferior aportada por la PCM fue relevante en el diagnóstico vestibular. Resultados: Se estudió a 44 pacientes. Tanto la sensibilidad como la especificidad de la PCM para detectar patología al estimular el canal semicircular lateral fue de 93 por ciento (IC95 por ciento: 84 por ciento-100 por ciento y 80 por ciento-100 por ciento respectivamente). En 16 por ciento (N =7) de los casos la PCM detectó patología del nervio vestibular inferior con PCC normal. Conclusiones: La PCM es un examen complementario útil en la evaluación de pacientes con sintomatología vestibular, puesto que tiene una alta sensibilidad y especificidad para detectar patología del nervio vestibular superior a través de la estimulación del canal semicircular lateral y además, aporta información sobre el estado del nervio vestibular inferior a través de la estimulación del canal semicircular posterior, que no aporta la PCC.

Introduction: The classic Fitzgerald-Hallpike caloric test (CCT) is usually utilized for evaluation of vestibular pathology. With this test, however, superior vestibular nerve function is assessed through stimulation of the lateral semicircular canal only. The minimal caloric test (MCT) allows for evaluation of both superior and inferior vestibular nerve function, through horizontal and posterior semicircular canals stimulation, respectively. The actual impact of MCT on the clinical evaluation of patients presenting with vestibular symptoms is unknown. Purpose: To quantify the diagnostic usefulness of MCT in patients with vestibular symptoms. Material and Method: Transversal diagnostic study. Sensitivity and specificity of MCT were obtained by comparing the lateral semicircular canal response in both MCT and the conventional caloric test. We assessed the number of cases in which the vestibular nerve function information obtained with MCT was relevant for vestibular diagnostic. Results: 44 patients were studied. The sensitivity and specificity of MCT to detect pathologic conditions via lateral semicircular canal stimulation were 93 percent (Cl 95 percent: 84 percent-100 percent and 80 percent-100 percent, respectively). In 16 percent (n =7) of the cases, MCT detected inferior vestibular nerve involvement with normal CCT Conclusions: MCT is a complementary test, which can be useful for evaluation of patients with vestibular symptoms, given its high sensitivity and specificity to detect superior vestibular nerve pathology through lateral semicircular canal stimulation. In addition, it provides information on the inferior vestibular nerve status, through posterior semicircular canal stimulation. The latter is not provided by conventional CCT.

Firing properties and classification of MVN neurons in rats / 华中科技大学学报（医学）（英德文版）

In order to know the effects of caloric stimulation on neuronal firing in medial vestibular nuclei (MVN) by middle ear irrigation, the middle ear was irrigated with ice (4 degrees C), hot (44 degrees C), and warm (37 degrees C) water, and the firing rate of MVN neuron was extracellularly recorded. The results showed that the firing rate of MVN neuron was changed by caloric stimulation, and the majority of MVN neurons showed excitation by irrigation with hot water and inhibition by ice water (type A). The neuronal firing was recovered immediately after the cessation of the stimulation. I It was concluded that the neuronal firing rate in MVN was changed by caloric stimulation in middle ear cavity. The response was different in various neurons.

Clinical evaluation of the function of the inferior vestibular nerve

A vectoelectronistagmografia (VENG) representa uma nova técnica de gravaçäo dos movimentos oculares horizontais, verticais e oblíquos, empregando três canais de registro. O principal interesse na utilizaçäo da VENG é representado pela possibilidade de estudar as respostas nistágmicas à estimulaçäo dos canais semicirculares verticais e nervo vestibular inferior, uma área do sistema vestibular que näo pode ser analisada por outros meios. A estimulaçäo de cada canal vertical é realizada através da prova rotatória pendular decrescente, colocando-se a cabeça fletida de 60- para trás e 45- para cada lado. O nistagmo resultante desta estimulaçäo é oblíquo. Só é possível estabelecer o diagnóstico das lesöes unilaterais dos canais superiores e posteriores diante da falta do fenômeno da compensaçäo vestibular para esses canais, ao contrário do que ocorre com os canais laterais. A estimulaçäo dos canais posteriores implica na gravaçäo de respostas que envolvem os nervos vestibulares inferiores e suas conexöes centrais. Neste estudo, podemos verificar que a compensaçäo vestibular para os canais verticais esteve ausente em 43,5% dos casos, mesmo quando os canais laterais apresentavam perfeita compensaçäo, em 46 casos de síndromes labirínticas. Alteraçöes do nervo vestibular inferior foram identificadas em 17 casos (36,9%). Esses achados sugerem que a exploraçäo específica dos canais verticais e nervo vestibular inferior possam tornar-se um importante teste vestibular para a rotina clínica