Divergent and point‐to‐point connections in the commissural pathway between the inferior colliculi

Abstract

The commissure of the inferior colliculus interconnects the left and right sides of the auditory midbrain and provides the final opportunity for interaction between the two sides of the auditory pathway at the subcortical level. Although the functional properties of the commissure are beginning to be revealed, the topographical organization of its connections is unknown. A combination of neuroanatomical tracing studies, 3D reconstruction, and neuronal density maps was used to study the commissural connections in rat. The results demonstrate that commissural neurons in the central nucleus of the inferior colliculus send a divergent projection to the equivalent frequency-band laminae in the central nucleus and dorsal and lateral cortices on the opposite side. The density of this projection, however, is weighted toward a point that matches the position of the tracer injection; consistent with a point-to-point emphasis in the wiring pattern. In the dorsal cortex of the inferior colliculus there may be two populations of neurons that project across the commissure, one projecting exclusively to the frequency-band laminae in the central nucleus and the other projecting diffusely to the dorsal cortex. Neurons in the lateral cortex of the inferior colliculus make only a very weak contribution to the commissural pathway. The point-to-point pattern of connections permits interactions between specific regions of corresponding frequency-band laminae, whereas the divergent projection pattern could subserve integration across the lamina. J. Comp. Neurol. 514:226–239, 2009. © 2009 Wiley-Liss, Inc.

Computer-assisted 3-D reconstructions of Golgi-impregnated neurons in the cortical regions of the inferior colliculus of rat

“…The interpretation of the caudal border between the CNIC and the DCIC in rat given by Faye-Lund and Osen (1985) and the present study is consistent with the existence of a transitional zone, not only with respect to the ascending and descending input (Malmierca, 2003;Malmierca et al, 2005), and intrinsic connections (Malmierca et al, 1995a;2009b) but also with respect to the cell types. Many NOS positive neurons in this region are bipolar (Coote and Rees, 2008) and they may correspond to some of the transitional neurons we describe here.…”

The superior paraolivary nucleus shapes temporal response properties of neurons in the inferior colliculus

“…However, the results herein imply that the network may be more complex, since firing rates decreased somewhat for the selective MFs and in some cases exhibited subtle increases for the unselective MFs. Such effects may be achieved if inhibitory interneurons are considered in the network (Oliver and Morest 1984; Malmierca et al 2009). For example, a timed disinhibition mediated by the SPON would enhance the IC SAM response up to the MF limit of SPON neurons (Kuwada and Batra 1999; Kadner and Berrebi 2008; Felix et al 2012).…”

Neural sensitivity to novel sounds in the rat's dorsal cortex of the inferior colliculus as revealed by evoked local field potentials

“…Other projections to the ICd include those from the ipsilateral ICc and ICx, all the major subdivisions of the contralateral IC, the auditory thalamus, and brainstem auditory structures (Cant and Benson, 2008;Gonzalez-Hernandez et al, 1987;Malmierca et al, 1995aMalmierca et al, , 2009bSaldaña and Merchán, 1992;Willard and Martin, 1983;Winer et al, 2002). The ICd projects to the dorsal part of the medial geniculate nucleus (Kudo and Niimi, 1978;Malmierca and Merchán, 2004;Wenstrup et al, 1994).…”