Periodotopic organization in the ICC of gerbils: A 2-deoxyglucose study

Abstract

Periodicity is an important property of many acoustic signals. In the central inferior colliculus (ICC) of the auditory brainstem pathway, frequency and periodicity information converge on a tonotopically organized network. Electrophysiological investigations demonstrate a marked degradation of temporal information in the ICC pertaining to the envelope of spectrally complex signals relative to that observed at the level of the auditory periphery. The temporal information appears to be transformed into a rate-place code and is represented topographically in an orientation orthogonal to the spectral frequency (tonotopic) axis. Additional evidence for orthogonal orientation of frequency and periodicity is derived from a magnetoencephalographic (MEG) study of human auditory cortex and from optical recordings in cat auditory cortex. 2-deoxyglucose labeling was used to investigate the topographic organization of frequency and periodicity information in the ICC of the Mongolian gerbil. The results of this study provide additional evidence for such topographic orthogonality, as well as for convergent information flow, suggesting that neurons in the ICC project to a specific subpopulation of cells in the low-frequency area of the auditory cortex that integrate information across separate periodotopically organized frequency bands.