Gap Detection in Auditory Cortex
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Strong evidence supports that for older adults, hearing loss and difficulty with speech comprehension in noisy environments is the result of temporal processing deficits in central auditory structures such as the auditory cortex. There is a general canonical circuit model of layer by layer serial information flow through the auditory cortex from the thalamus, before information is projected back into inferior colliculus neurons. However the specific cortical circuits and cell types which regulate temporal processing through the auditory cortex are still unknown and not linked to behavior. The auditory cortex contributes to temporal acuity in receiving auditory stimuli. Temporal acuity is used, for example, for brief noise gap detection and discriminating between similar phonemes. Impairments to temporal activity can cause speech perception deficits. In this study, I tested gap detection behavior in mice. To do this, I measured how their startle responses were modulated by gaps in continuous background noise. The presence of the gap attenuates the startle response to the stimulus, so that measuring the startle response gives a measure of temporal acuity by assessing gap detection behavior. I used a technology called optogenetics to manipulate brain activity during this behavior. Optogenetics allows for the gaps to be paired with a laser pulse that silences auditory cortex neurons and allowed me to see how gap detection is impaired by temporally precise suppression of auditory cortex. By probing cortex circuit mechanisms through layer-specific optogenetic silencing before and after gap, I found that layer-specific silencing of auditory cortex neuron populations in layers four and five suggests behavior in accordance with the canonical model.