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Lookup NU author(s): Dr Llwyd Orton, Professor Paul Poon, Professor Adrian ReesORCiD
The auditory pathways coursing through the brainstem are organized bilaterally in mirror image about the midline and at several levels the two sides are interconnected. One of the most prominent points of interconnection is the commissure of the inferior colliculus (CoIC). Anatomical studies have revealed that these fibers make reciprocal connections which follow the tonotopic organization of the inferior colliculus (IC), and that the commissure contains both excitatory and, albeit fewer, inhibitory fibers. The role of these connections in sound processing is largely unknown. Here we describe a method to address this question in the anaesthetized guinea pig. We used a cryoloop placed on one IC to produce reversible deactivation while recording electrophysiological responses to sounds in both ICs. We recorded single units, multi-unit clusters and local field potentials (LFPs) before, during and after cooling. The degree and spread of cooling was measured with a thermocouple placed in the IC and other auditory structures. Cooling sufficient to eliminate firing was restricted to the IC contacted by the cryoloop. The temperature of other auditory brainstem structures, including the contralateral IC and the cochlea were minimally affected. Cooling below 20 degrees C reduced or eliminated the firing of action potentials in frequency laminae at depths corresponding to characteristic frequencies up to similar to 8 kHz. Modulation of neural activity also occurred in the un-cooled IC with changes in single unit firing and LFPs. Components of LFPs signaling lemniscal afferent input to the IC showed little change in amplitude or latency with cooling, whereas the later components, which likely reflect inter- and intra-collicular processing, showed marked changes inform and amplitude. We conclude that the cryoloop is an effective method of selectively deactivating one IC in guinea pig, and demonstrate that auditory processing in the IC is strongly influenced by the other.
Author(s): Orton LD, Poon PWF, Rees A
Publication type: Article
Publication status: Published
Journal: Frontiers in Neural Circuits
Year: 2012
Volume: 6
Print publication date: 14/12/2012
Date deposited: 24/01/2013
ISSN (electronic): 1662-5110
Publisher: Frontiers Research Foundation
URL: http://dx.doi.org/10.3389/fncir.2012.00100
DOI: 10.3389/fncir.2012.00100
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