Abstract
Connections unifying hemispheric sensory representations of vision and touch occur in cortex, but for hearing, commissural connections earlier in the pathway may be important. The brainstem auditory pathways course bilaterally to the inferior colliculi (ICs). Each IC represents one side of auditory space but they are interconnected by a commissure. By deactivating one IC in guinea pig with cooling or microdialysis of procaine, and recording neural activity to sound in the other, we found that commissural input influences fundamental aspects of auditory processing. The areas of nonV frequency response areas (FRAs) were modulated, but the areas of almost all V-shaped FRAs were not. The supra-threshold sensitivity of rate level functions decreased during deactivation and the ability to signal changes in sound level was decremented. This commissural enhancement suggests the ICs should be viewed as a single entity in which the representation of sound in each is governed by the other.
Highlights
The bilateral organization of the pathways mediating the orienting senses is optimized to detect stimuli occurring in the right and left halves of space relative to the body's midline
By deactivating one IC in guinea pig with cooling or microdialysis of procaine, and recording neural activity to sound in the other, we found that commissural input influences fundamental aspects of auditory processing
Our findings show that intercollicular commissural connections regulate firing and are a major determinant of the receptive fields of IC neurons
Summary
The bilateral organization of the pathways mediating the orienting senses is optimized to detect stimuli occurring in the right and left halves of space relative to the body's midline. While the left and right pathways are distinct, they involve crossed connections at several levels (Moore and Osen, 1979; Glendenning and Masterton, 1983; Glendenning et al, 1985; Oliver, 2000; Cant and Benson, 2003) Some of these crossed connections, such as those between the cochlear nuclei and the superior olivary complex, occur between different levels in the hierarchy and mediate interactions that extract the interaural disparities underlying sound localization. Such connections have been termed the acoustic chiasm (Glendenning et al, 1985).
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