Auditory space representation and its plasticity in the shell of the inferior colliculus

• Applicant: Dr. Meike Marie Rogalla
• Subject Area: Cognitive, Systems and Behavioural Neurobiology ; Experimental and Theoretical Network Neuroscience
• Term: from 2022 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509509296

Spatial hearing enables humans and animals to localise sounds in their vicinity which contributes to survival. In the auditory system, locations of sound sources are derived centrally from binaural and monaural cues. In the case of unilateral hearing loss, binaural cues are not available, limiting spatial hearing which impairs speech processing and overall hearing ability. However, monaurally occluded humans and animals can regain sensitivity in sound localisation when binaural cues are absent. It is assumed that the observable re-learning of sound localisation relies on the context-dependent re-calibration of auditory space by monaural cues. Thus, central auditory plasticity mechanisms must exist to re-weight binaural and monaural cues during task engagement. The shell of the inferior colliculus (IC) may act as a dominant site for this spatial plasticity. When silencing descending projections from the primary auditory cortex, which directly contact shell IC, animals are unable to re-learn sound localisation, indicating the strong role of shell IC in spatial plasticity. However, the physiological representation of space in the mammalian shell IC and the mechanisms of adaptation to altered input are poorly understood. Closing this gap in knowledge would improve our understanding of how learning exercises might support plasticity processes and how they could be applied as a simple approach to improve sound localisation following monaural hearing loss. The major objectives of this project are to investigate the representation of auditory space in the shell IC and to reveal mechanisms of central auditory plasticity following monaural hearing loss in the behaving animal. To this end, we will use a combination of 2-photon Ca2+-imaging and behavioural assays in head-fixed mice. This cutting-edge technique enables monitoring activity of the same neurons in the shell IC over a duration of weeks to assess plasticity of over time. We will perform a systematic investigation of auditory space representation in the shell IC of normal hearing vs. unilaterally hearing-impaired mice in passive listening experiments. In the next step, we will test how learning drives the re-organisation of auditory space representation in the shell IC following monaural hearing loss. Mice will be trained to discriminate between sound presentations from the left and the right hemifield during imaging. Animals will receive a unilateral earplug to investigate dynamics of spatial tuning in the shell IC while mice re-learn to localise sounds. The last experiment will use the same behavioural approach but with a focus on cortical input into the shell IC. Cortico-collicular projections will be visualised in the shell IC during re-learning of sound localisation using axonal Ca2+-imaging. Our results will further establish the role of the shell IC in spatial hearing and deepen our understanding about the physiology of sensory plasticity in adulthood and binaural hearing in general.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Pierre F. Apostolides, Ph.D.