The mammalian auditory system has evolved, in part, to adapt to the acoustic environment and meet the needs of particular species in that environment. The accurate recognition and localization of sound are important aspects of hearing and provide an animal with information that can be used to guide behavior. When other sensory cues are not available, as in darkness, localized sound may be the only information available to avoid obstacles, flee predators, or locate prey. For blind individuals, sound cues are often crucial for simply moving from one location to another. While the neural mediation of sound source identification is well-examined, there is relatively little understanding of locomotor behavior reliant on, but not necessarily directed at, localized sounds. The broad goal of the proposed project is to begin examining the role of the central auditory pathway in mediating sound-guided movement through a field in the absence of other sensory cues. Experiments are proposed to examine sound-guided spatial navigation as mediated by the inferior colliculus (IC) of the auditory midbrain. Pigmented rats are subjects of the planned experiments. These animals are adept at various learning paradigms including situations requiring spatial navigation--the movement around barriers in a field to reach a goal. Rats are trained to successfully navigate around barriers in a circular field by learning to move sequentially toward a series of sequentially presented broadband sounds and reach a goal. By following the spatially and temporally static noise bursts, animals avoid obstacles and blind alleys. Following baseline behavioral testing, a neurotoxin is used to destroy neurons of central nucleus of IC or external cortex of IC sparing lemniscal afferents, brachial efferents and other fibers of passage. Post-lesion sound-guided navigation trials are then conducted. In this way, a relatively clear assessment of the function of cells of CNIC and ECIC, which are known to physiologically encode features of sound location, in sound guided behavior is possible. Accuracy, time and pattern of sound-guided navigation are analyzed by examining videotaped records, and behavior of lesioned animals is compared to pre-lesion navigation and that of normal conspecifics. Neuroanatomical analyses are used to clarify behavioral results. Characteristics of navigation by normal and IC-damaged animals should provide foundations for further hypotheses about mediation of sound-guided behavior by auditory brainstem structures. Navigational strategies of lesioned animals, lesion-related cell death in lower auditory brainstem structures, or correlation of specific IC subdivision lesions with specific behavioral deficits should lay the foundation for future research proposals to examine recovery of function after auditory pathway damage. Future experiments could examine deficits sound-guided behavior following audiogenic seizure-induced transmitter disruption in IC, or the efficacy with which neural grafts restore lost behavior following damage to IC or its specific subdivisions.
| Zrull, M C; Coleman, J R (1999) Spatial sound detection and the role of the inferior colliculus in the Long-Evans rat. Acta Otolaryngol 119:326-32 |
