Henry E. Heffner - US grants

The proposed research entails the behavioral analysis of the role of auditory cortex by ablation-behavior techniques. The ultimate goal is to discover the psychological functions of auditory cortex which enable humans to respond appropriately to sounds in their enviroment. The short-range goals concern the behavioral assessment of the role of auditory cortex in processing species-specific vocalizations. Specifically, the effect of unilateral and bilateral auditory cortex lesions in monkeys is to be studied by the application of tests designed to assess the psychological as well as the sensory aspects of hearing. By the experimental study of the basic psychological processes in animals, it is hoped to obtain information relevant to human psychological processes and the way in which these capacities fragment as the result of brain damage.

The purpose of the proposed research is to investigate the neurological basis of the perception of vocal communications in Japanese macaques by use of the ablation-behavior technique. This consists of determining the effects of experimental lesions on the ability of animals to perceive their vocal communication sounds. Because Japanese macaques possess a cortical mechanism for the perception of their vocal communications which is lateralized to the left hemisphere, they provide a model for studying the neurology of human speech perception. The specific experiments consist of 1) determining the degree to which the perception of vocal communications in Japanese macaques is lateralized to the left hemisphere, 2) determining whether the inability of Japanese macaques to categorize their vocalizations following cortical ablation is accompanied by deficits in the ability to discriminate frequency, intensity or temporal aspects of sound, 3) investigating the "species-specific" nature of the perceptual mechanism by determining whether non-Japanese macaques lose the ability to categorize Japanese macaque vocalizations following cortical ablation, and 4) determining the effect of temporal lobe lesions on evoked potentials. Because of their behavioral and neurological similarities with humans, macaques provide an animal model for determining the effects of stroke on communication. Because these animals have a neurological specialization for the perception of their vocal communications which is similar to the human specialization for speech perception, these experiments may enable clinicians to better understand the effects of brain damage in humans on the perception of speech. However, the long-range goals are to further our understanding of how the brain works and to provide an animal model for the development of techniques for repairing damage to the speech areas (such as neural transplants) when such techniques become available.

The purpose of the proposed research is to investigate the neurological basis of the perception of vocal communications in Japanese macaques by use of the ablation-behavior technique. This consists of determining the effects of experimental lesions on the ability of animals to perceive their vocal communication sounds. Because Japanese macaques possess a cortical mechanism for the perception of their vocal communications which is lateralized to the left hemisphere, they provide a model for studying the neurology of human speech perception. The specific experiments consist of 1) determining the degree to which the perception of vocal communications in Japanese macaques is lateralized to the left hemisphere, 2) determining whether the inability of Japanese macaques to categorize their vocalizations following cortical ablation is accompanied by deficits in the ability to discriminate frequency, intensity or temporal aspects of sound, 3) investigating the "species-specific" nature of the perceptual mechanism by determining whether non-Japanese macaques lose the ability to categorize Japanese macaque vocalizations following cortical ablation, and 4) determining the effect of temporal lobe lesions on evoked potentials. Because of their behavioral and neurological similarities with humans, macaques provide an animal model for determining the effects of stroke on communication. Because these animals have a neurological specialization for the perception of their vocal communications which is similar to the human specialization for speech perception, these experiments may enable clinicians to better understand the effects of brain damage in humans on the perception of speech. However, the long-range goals are to further our understanding of how the brain works and to provide an animal model for the development of techniques for repairing damage to the speech areas (such as neural transplants) when such techniques become available.

[unreadable] DESCRIPTION (provided by applicant): The purpose of this proposal is to develop techniques for determining the nature of tinnitus experienced by animals so that the mechanisms underlying tinnitus can be studied experimentally. The type of tinnitus to be studied is the transient tinnitus caused by exposure to loud tones. The project consists of three parts. First, a two-choice procedure will be developed to determine the pitch of an animal's tinnitus. Rats will be trained to rank-order the pitch of external sounds presented to each ear separately via headphones. They will then be tested on their ability to match the pitch of tinnitus that is induced in one ear with external tones presented to the other ear. Second, the auditory brainstem response (ABR) will be calibrated for use as a rapid means of determining hearing loss caused by exposure to loud tones. We will obtain both behavioral and ABR thresholds in the same animals before and after exposure to loud tones. The results will show if the two measures give the same estimate of hearing loss and, if not, whether a correction factor can be used to determine the behavioral hearing loss from the ABR. Finally, the cochleas of the animals used in the development of these procedures will be examined to obtain exploratory information regarding the relation between tinnitus, hearing loss, and damage to the Organ of Corti. The ultimate goal of this project is to devise tools to be used to discover the cause of tinnitus and to develop effective treatments. Knowing the pitch of an animal's tinnitus is necessary to distinguish between physiological changes due to hearing loss from those due to tinnitus. [unreadable] [unreadable]