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Original Article

The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs

El efecto del espectro de marcadores de brecha sobre las respuestas auditivas evocadas por brecha en el colículo inferior y la corteza auditiva de cobayos

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Pages 521-527 | Published online: 07 Jul 2009
 

Abstract

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500–8 000 Hz, 500–16 000 Hz, 500–32 000 Hz, and 16 000–32 000 Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2 ms with the bandwidth change. However, the gap threshold in the high frequency region (16 000–32 000 Hz) was comparable to that of the low frequency region (500–16 000 Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.

Sumario

El objetivo de este estudio es verificar los efectos del espectro de marcadores de brecha sobre las respuestas auditivas evocadas por una brecha. Se registraron los potenciales evocados por brecha utilizando electrodos implantados en el colículo inferior (IC) y la corteza auditiva (AC) de cobayos. Los marcadores de brecha fueron bursts de ruido en cuatro bandas de frecuencia (500–8000 Hz, 500–16 000 Hz, 500–32 000 Hz and 16 000–32 000 Hz), y se evaluaron a tres niveles sonoros. Se midió la respuesta de inicio del marcador post-brecha para obtener el umbral de respuesta de brecha, y establecer las funciones de ingreso-salida para latencia y amplitud. Al igual que en estudios conductuales previos, se encontró que el umbral de respuesta de brecha disminuyó con el incremento de los anchos de banda del marcador. Este cambio fue más significativo a nivel cortical en donde el umbral promediado de brecha disminuyó en aproximadamente 2 mseg con el cambio de ancho de banda. Sin embargo, el umbral de brecha en la región de alta frecuencia (16 000–32 000 Hz) fue comparable al umbral de la región de baja frecuencia (500–16 000 Hz). Estos resultados sugieren que el ancho de banda total de todos los canales auditivos reclutados determina la resolución temporal medida en los potenciales evocados por brecha.

Acronyms
IC=

Inferior colliculus

AC=

Auditory cortex

MB=

Marker band

TDT=

Tucker-Davis Technologies

ANOVA=

Analysis of variance

Acronyms
IC=

Inferior colliculus

AC=

Auditory cortex

MB=

Marker band

TDT=

Tucker-Davis Technologies

ANOVA=

Analysis of variance

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