Tonotopic organization in the inferior colliculus of the rat demonstrated with the 2-deoxyglucose method

We studied the tonotopic organization in the inferior colliculus of the rat with the 2-deoxyglucose method. Isofrequency bands were observed in the central nucleus of the inferior colliculus. In coronal sections, higher sound frequencies elicited bands that were located more ventrally. At caudal levels of the inferior colliculus, isofrequency bands were relatively short and tilted slightly downward toward the midsagittal plane. As the plane of section moved more rostrally, isofrequency bands gradually lengthened, their orientation first turned horizontally and continued with a downward tilt toward the lateral aspect of the brainstem. At rostral levels, high-frequency (greater than 8000 Hz) bands showed more significant increases in length than low-frequency (less than 4000 Hz) bands. Thus, the amount of tissue in the inferior colliculus devoted to higher frequencies was significantly more than that for lower frequencies. In sagittal sections, the isofrequency band moved from a dorsoposterior position to a ventroanterior one as the plane of section moved more laterally. A three-dimensional model of isofrequency planes was reconstructed from the above data.