ABSTRACT
Objective:Clinical application of middle-latency auditor evoked potential (MLAEPs) has been increasing, highlighting the importance of understanding the nature of P50,a componentof middle-latency auditory evoked potential. We manipulated stimulus frequency bands in auditory stimuli in order to investigate the nature of P50 in human auditory evoked potentials.Methods:Two paradigms have been used to obtain P50: one is a conditioning /testing paradigm in which paired of pure tone (1000Hz) are delivered, and the other was presented paired of clicks, both with an intensity of 60 dB sound pressure level above the auditory threshold. A total of 30 healthy volunteers were recruited for this study among Center of genetic engineering (fifteen man and fifteen women, mean age of 36,5). All without consumption of caffeine, cigarettes and drugs. Results:No statistically significant differences occurred between the P50 amplitudes and latencies for the pure tone and those for the clicks.Conclusions:Ourpresent results indicate that P50 in humans may reflect a feed-forward mechanism of the brain where a preceding stimulus drives sensory gating mechanisms in preparation for a second stimulus, but the contained frequency doesn't influence on the P50. Both types (tones or clicks) can be used in the exploration of patient with this evoked potential
ABSTRACT
El análisis del reflejo vestíbulo-cólico, que consiste en la activación de los vestibulares primarios, aporta una una valiosa información sobre la fisiología vestibular y es una herramienta útil para la evaluación de pacientes con alteraciones vestibulares. El objetivo de este trabajo es determinar las respuestas vestíbulo-cólicas mediante los estímulos con clicks de alta intensidad y mediante estímulos eléctricos transmastoideos (estimulación galvánica), establecer los valores de referencia y evaluar los parámetros según la edad. Se evaluaron a 20 personas sanas asintomáticas: en cada uno de ellos se evaluó la respuesta vestíbulo-cólica ante la estimulación con clicks, donde se registró una respuesta bifásica p13-n23 y ante la estimulación galvánica, donde se obtuvo una respuesta positivo-negativa p1-n1. Se utilizaron dos electrodos de registro, uno activo, ubicado en el tercio superior del músculo esternocleidomastoideo y otro de referencia ubicado en la unión esternoclavicular ipsilateral. Se analizaron las latencias, las amplitudes de los componentes y los índices de asimetría de amplitudes;las medianas de las latencias de los componentes p13 y n23 fueron significativamente menores que las de los componentes p1-n1; las amplitudes, tras la estimulación galvánica fueron menores que las obtenidas con clicks. Asimismo, se halló una correlación negativa entre la amplitud de la respuestas y la edad de los sujetos. El índice de asimetría de amplitudes fue similar en ambos paradigmas. El empleo de ambos tipos de estímulo es complementario para el estudio de la fisiología vestibular
The assessment of the vestibulocollic reflex consists of the activation of primary vestibular afferents; it also provides valuable information about vestibular physiology, and thus, can be used as a diagnostic tool in vestibular disorders. The aim of this research work is to evaluate this vestibule-collic response by using high intensity auditory as well as galvanic stimuli in order to provide normal referente values and search a correlation between each parameter and the age of individuals. Twenty healthy individuals of both sexes were subjetct to an assessment and after high intensity clicks a p13-n23 a response was obtained; furthermore, after galvanic stimuli a p1-n1 response was obtained. Two surface electrodes (active and reference) were used to read the responses obtained. Latency and amplitudes of p13-n23 and p1-n1 responses and asymmetry indexes were analyzed. Median latencies of p13-n23 responses were shorter than those of p1-n1 responses; and amplitudes of p1-n1 were smaller than those of p13-n23. It was observed a negative correlation between amplitudes of responses and age of the subjets. Asymmetry indexes were similar in both paradigms. The assessment of the vestibulo-collic reflex by using both clicks and galvanic stimulation gives valuable information about vestibular physiology