LAMINAR FINE-STRUCTURE OF FREQUENCY ORGANIZATION IN AUDITORY MIDBRAIN

The perception of sound is based on signal processing by a bank of fre quency-selective auditory filters, the so-called critical bands(1-3). Here we investigate how the internal frequency organization of the mai n auditory midbrain station, the central nucleus of the inferior colli culus (ICC), might contribute to the generation of the critical-band b ehaviour of its neurons. We find a unique spatial arrangement of the f requency distribution in the ICC that correlates with psychophysical c ritical-band characteristics. Systematic frequency discontinuities alo ng the main tonotopic axis, in combination with a smooth frequency gra dient orthogonal to the main tonotopic organization of cat ICC, reflec t a layering of the frequency organization paralleling its anatomical laminae. This layered frequency organization is characterized by const ant frequency ratios of corresponding locations on neighboring laminae and may provide a spatial framework for the generation of critical ba nds and for signal processing within(4) and across' frequency bands fo r the analysis of sound.