Topographical projection from the superior colliculus to the nucleus of the brachium of the inferior colliculus in the ferret: convergence of visual and auditory information

Abstract

The normal maturation of the auditory space map in the deeper layers of the ferret superior colliculus (SC) depends on signals provided by the super®cial visual layers, but it is unknown where or how these signals in¯uence the developing auditory responses. Here we report that tracer injections in the super®cial layers label axons with en passant and terminal boutons, both in the deeper layers of the SC and in their primary source of auditory input, the nucleus of the brachium of the inferior colliculus (nBIC). Electron microscopy con®rmed that biocytin-labelled SC axons form axodendritic synapses on nBIC neurons. Injections of biotinylated dextran amine in the nBIC resulted in anterograde labelling in the deeper layers of the SC, as well as retrogradely labelled super®cial and deep SC neurons, whose distribution varied systematically with the rostrocaudal placement of the injection sites in the nBIC. Topographical order in the projection from the SC to the ipsilateral nBIC was con®rmed usinḡ uorescent microspheres. We demonstrated the existence of functional SC-nBIC connections by making whole-cell current-clamp recordings from young ferret slices. Both monosynaptic and polysynaptic EPSPs were generated by electrical stimulation of either the super®cial or deep SC layers. In addition to unimodal auditory units, both visual and bimodal visual±auditory units were recorded in the nBIC in vivo and their incidence was higher in juvenile ferrets than in adults. The SC-nBIC circuit provides a potential means by which visual and other sensory or premotor signals may be delivered to the nBIC to calibrate the representation of auditory space.

Reorganization of the Connectivity of Cortical Field DZ in Congenitally Deaf Cat

“…Visual or visual related (saccadic) information are reaching the different auditory relays such as the inferior colliculus and the MGB [125]–[127]. These visual activities can originate from direct retinal inputs [128], [129] or from projections from the upper layers of the superior colliculus [130] reaching the inferior colliculus. In some species (rodents and ferrets), the primary auditory cortex is receiving direct projections from visual areas [131], which is not the case in the cat and monkey (present study, [132].…”

Population-Wide Bias of Surround Suppression in Auditory Spatial Receptive Fields of the Owl's Midbrain

“…The superior colliculus in mammals possesses a topographic representation of both visual and auditory space, where frontal space overrepresentation has been observed in numerous species (Drager and Hubel, 1976; Doubell et al, 2000). The visual and somatosensory cortices also show overrepresentation of the foveal region (Yang et al, 1992; Kautz and Wagner, 1998; Zhang et al, 1999) and the face and hands (Penfield and Boldrey, 1937; Fujita and Konishi, 1991), respectively.…”

Visual- and saccade-related signals in the primate inferior colliculus

“…We and others have found that the primate IC contains neurons with activity that depends on eye position (15)(16)(17), a signal that is necessary for compensating for the dissociations between visual and auditory spatial locations that occur naturally when the eyes move. There is also anatomical evidence for projections to the IC from the retina (18)(19)(20), visual cortex (21), and the SC (22,23 Gutfreund et al (14) in anesthetized owls suggests that visual inputs to the IC are prevalent, but normally silent.…”