Exposure of the topographic representative of betweenears characteristicsof the middlebrain section of the hearing (inferior colliculus)

The major function of the inferior colliculus is connected with the sound source localization.The leading role in sound source localization is played by binaural mechanismsof sound signals analysis in the auditory (aural, acoustic) system. Interaural differencesin time of sound coming to right and left ears is one of binaural factors whichdefine the sound source localization. Interaural delay (ΔТ) serves as a basic sign of lowfrequentsound localization (up to 2 kHz). By nowadays the problem of neurons topicalorganization (neurons, which localize sound source) in colliculus inferior is not solved.Basic principles of nerve-elements spatial organization in binaural acoustic system arenot clear. In this connection the present work was directed to establish topographicalpresentation of signs, which define the place of sound signal, in the acoustic system. Themain attention is drawn to the revealing of the sound localization signs distribution regularityinside of one isofrequent layer.The studying was held on healthy guinea-pigs with well-expressed Prayers reflex, inthe conditions of acute experiment with the application of narcosis, sedatives and anesthetics.The method of multichannel registration (by microelectrode beam) was used asthe basic one in the investigation of neurons extracellular impulse activity. Single neuronsimpulse activity was analysed in binaural presentation of lowfrequent tonal andsound signals (up to 2 kHz) with different interaural delay magnitude. By the descriptionsof neuronal selectiveness to interaural delay the mapping of inferior colliculus isofrequentlayers was held during this work.The investigation of inferior colliculus neurons topical organization (of neurons, selectiveto interaural delay magnitude) showed, that by influence of broadband soundmagnitude of optimal delay gradually increases while moving from the rostral to caudalarea of the inferior colliculus. Despite the differences in the magnitude of optimal delay,when the influence of lowfrequent sounds occurs, the spatial distribution of neurons revealsthe similar tendency to optimal delay increasing in the rostracaudal direction.So, the distribution of optimal interaural delay in the inferior colliculus reveals thetendency to increase in the rostracaudal direction.

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