Informing the next generation of auditory midbrain implants : neuronal population dynamics in the auditory cortex and midbrain, and the potentials of optogenetic stimulation

Student thesis: Doctoral Thesis

Abstract

The performance of current generation central auditory neuroprosthetics lags behind the cochlear implant. As these new devices utilise speech processing algorithms based on the cochlea, more information may be required regarding the neuronal population activity of potential prosthetic sites, in order to optimise stimulation to mimic the area’s natural inputs and achieve useful sound perception. Additionally, electrode based devices afford poor spatial resolution, which optogenetics may solve. Simultaneous silicon probe recordings were performed in the inferior colliculus (IC) and auditory cortex (AC) of awake, head-fixed mice, and repetitions of natural sound stimuli played. The two areas are different in their general cell population metrics, levels of inter-trial LFP coherence, and neuronal entrainment, with the AC favouring entrainment frequencies below 30Hz and the IC apparently entraining over a wider range of 2-200Hz.The proportion of putative AC narrow-spiking interneurons is higher during natural sounds as opposed to spontaneous activity alone. Using linear classification analysis, a spike rate code was generally found to be sufficient for distinguishing between natural sound stimuli, in both the AC and IC. However, the IC achieved comparable performance to the AC using fewer single ormulti units. This could be due to the lower trial-trial variability (Fano factor) of the ICcell population. Dimensionality reduction revealed, qualitatively, the presence of distinct cell populations in both brain areas, responding to different aspects of the natural sound.A viral injection protocol for expression of the Chronos opsin through the depth of themouse ICC was optimised, and light activation confirmed. A control system for a µLEDdevice was created and used in a pilot experiment, which served to highlight the importance of artefact-reducing device design. The findings indicate that IC neurons tend to fire in the same way (i.e. more reliably) to successive repetitions of natural sound when compared to the auditory cortex, and that AC narrow-spiking interneurons may have different functions between spontaneous and evoked activity. Optogenetics is a promising approach to improving auditory implant resolution, given well designed light delivery devices and accompanying software.
Date of Award21 Aug 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorShuzo Sakata (Supervisor) & Keith Mathieson (Supervisor)

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