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INTRODUCTION AND OBJECTIVE: Auditory steady state responses to continuous amplitude modulated tones at rates between 70 and 110Hz, have been proposed as a feasible alternative to objective frequency specific audiometry in cochlear implant subjects. The aim of the present study is to obtain physiological thresholds by means of auditory steady-state response in cochlear implant patients (Clarion HiRes 90K), with acoustic stimulation, on free field conditions and to verify its biological origin. METHODS: 11 subjects comprised the sample. Four amplitude modulated tones of 500, 1000, 2000 and 4000Hz were used as stimuli, using the multiple frequency technique. The recording of auditory steady-state response was also recorded at 0dB HL of intensity, non-specific stimulus and using a masking technique. RESULTS: The study enabled the electrophysiological thresholds to be obtained for each subject of the explored sample. There were no auditory steady-state responses at either 0dB or non-specific stimulus recordings. It was possible to obtain the masking thresholds. A difference was identified between behavioral and electrophysiological thresholds of -6±16, -2±13, 0±22 and -8±18dB at frequencies of 500, 1000, 2000 and 4000Hz respectively. CONCLUSIONS: The auditory steady state response seems to be a suitable technique to evaluate the hearing threshold in cochlear implant subjects.

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El registro de potenciales evocados auditivos de estado estable (PEAee) ha alcanzado una amplia difusión en la práctica clínica audiológica en años recientes, debido a que sus características favorecen la evaluación objetiva de la audición, principalmente porque son generados por estímulos acústicos con especificidad en frecuencia y por la posibilidad de ser detectados de forma automática por medio de indicadores estadísticos; sin embargo, los neurogeneradores de los PEAee a múltiples frecuencias (PEAeeMf) no han sido ampliamente estudiados y no existe consenso en la literatura revisada en localizar con precisión sus bases neurales. La discusión sobre la naturaleza de los generadores de los PEAee es causa de controversia entre la comunidad científica. Varios autores han postulado que la respuesta de estado estable se obtiene por superposición de respuestas transientes, mientras que otros estudios sugieren que el PEAee refleja la activación de un ritmo neuronal intrínseco y, por tanto, la activación de neurogeneradores específicos. La presente revisión bibliográfica ha sido realizada con el propósito de analizar críticamente aquellos estudios que evalúan los generadores de esta técnica de potenciales evocados; para definir si existe o no consenso en la identificación y caracterización de sus bases neurales, así como evaluar la pertinencia de realizar un estudio de localización de sus neurogeneradores aplicando métodos de solución del problema inverso para la localización de fuentes cerebrales, introducidos recientemente en el campo de las neurociencias.

The recording of auditory steady state response (ASSR) has been expanded recently in audiological clinical practice, as a result of numerous advantages of this technique. Mainly it is generated by specific frequency acoustic stimulus and also for the possibility of automatic detection of response by applying statistic indicators. However the neural generators of multiple frequency ASSR has not been widely studied, and there is not clear consensus in the review reports about precise localization of neural generators of ASSR. The discussion of nature of ASSR generators is cause of severe controversy in scientific community. Many authors have been postulated that ASSR is generated as superposition of transient responses. Meanwhile others proposed that it is reflect the specific intrinsic neural rhythm activation and as a result is generated by specific neural sources. The present bibliographic review has been designed with the aim of critical analysis of studies that have been evaluated the brain sources of multiple frequency ASSR to define if there is or not any consensus about identification and characterization of ASSR generators. Also this review address to identification of feasibility to develop a new research for ASSR Sources localization applying novel inverse solution methods recently introduced in neurosciences.

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