Different Binaural Inputs Subdividing Isofrequency Planes in Chick Inferior Colliculus: Evidence from 2-Deoxyglucose

Abstract

Recently, Scheich (1983) has mapped the functional organization of field L, the avian analogue of the mammalian auditory cortex, in monaural domestic chicks using the 2-deoxyglucose technique (Sokoloff et al., 1974). He provided evidence that the field contains two columnar systems with different input from the two ears. One of these systems consists of three bands, a rostral, an intermediate, and a caudal one, all oriented orthogonal to the course of isofrequency contours. This system therefore resembles the organization described in cat auditory cortex (Abeles and Goldstein, 1970). The second system concerns the intermediate band only. This band shows multiple alternating columns of ipsi- vs. contralateral dominant input, which are roughly parallel to the course of isofrequency contours (Heil and Scheich, 1985). In order to clarify whether these two columnar systems are generated in the forebrain or whether they can be observed at levels below field L, we have analyzed 2-deoxyglucose patterns in the lower auditory system of monaural chicks, and we found evidence for segregated areas of different binaural interactions in the midbrain nucleus mesencephalicus lateralis, pars dorsalis (MLD), the avian inferior colliculus homologue.