Hearing and Communication Laboratory

Department of Neurobiology

Analyses of Communication Sounds in Auditory Midbrain
Principal Investigator: Christine Portfors
Funding Source: National Institute on Deafness and other Communication Disorders

The goal of this research is to understand how neurons in the midbrain process social vocalizations. Social vocalizations of animals are spectrally and temporally complex, and their analysis requires the integration of spectral and temporal information. One form of integration is performed by combination-sensitive neurons. These neurons respond best to combinations of spectrally or temporally distinct elements in complex sounds. In auditory cortex, it is known that combination sensitivity underlies selectivity to species-specific social vocalizations. Recently it has been found that combination sensitivity is a common feature of neurons in the auditory midbrain of the mustached bat, and that these response properties are created there. This suggests that combination sensitivity contributes to selectivity among social vocalizations in the midbrain. Virtually nothing is known regarding the extent of selectivity to social vocalizations in the inferior colliculus (IC) of mammals. The proposed research examines selectivity to social vocalizations in the IC, and investigates whether combination sensitivity contributes to the selectivity. The significance of this research is in gaining an understanding of how the emergence of combination-sensitive response properties in the auditory midbrain contributes to emergence of selectivity to social vocalizations. This will contribute to our understanding of how social vocalizations are processed at different levels of the ascending auditory system.

This research focuses on the mustached bat, in which combination sensitivity is widespread throughout the IC. Aim 1 examines responses of single units in three frequency band representations of the IC to single and combinations of stimuli. Excitatory, facilitatory and inhibitory frequency response areas will be examined. In auditory cortex, these response areas often explain responses to social vocalizations. Aim 2 investigates neuronal selectivity to social vocalizations of the mustached bat. Fourteen vocalizations that contain nearly all the elements of social calls in the mustached bat's repertoire will be used as stimuli and selectivity assessed. The third aim will test the contribution of combination sensitivity to selectivity among the calls. Calls that elicit the best response will be separated into their harmonic components and basic acoustic elements. Responses to these individual components and their combinations will be tested to identify whether the combination of particular elements contributes to response selectivity. Results will establish the extent of selectivity among social vocalizations in the IC, the contribution of combination sensitivity to selectivity, and differences in selectivity to social vocalizations between the IC and auditory cortex.