Auditory feedback is required for both vocal learning in juveniles and vocal maintenance in adults. However, the neural mechanisms by which auditory feedback influences vocal motor control are still elusive. Finding the central neural representation of auditory feedback will be the first step towards fully understanding these mechanisms. The goal of my thesis is to functionally identify the central pathway conveying singing-related auditory feedback in songbirds. Prior studies have identified a neural circuit necessary for singing, known as the "song system". My hypothesis is that the source of auditory drive to the song system also conveys auditory feedback information. This thesis took two steps to test the above hypothesis: first, to identify the central pathway that drives the auditory activity in the song system in anaesthetized birds. Second, to test whether the same pathway also conveys auditory feedback in singing birds.;In the first step, using in vivo electrophysiology, I found that reversibly inactivating thalamic auditory nucleus Oviodalis (OV) completely blocked BOS-evoked auditory response in the song nucleus HVC in anaesthetized zebra finches. Low frequency stimulation in OV evoked synaptic responses in HVC with latencies and profiles consistent with the noise-evoked auditory responses that could be recorded in this nucleus. High frequency stimulation in OV attenuated the selective HVC auditory responses to BOS-playback. These results demonstrate that the activity in the OV pathway is both necessary and sufficient to drive auditory activity in HVC in anaesthetized zebra finches, indicating that OV is the indirect source of auditory drive to the song system.;In the second step, I tested whether changing activity in OV during singing disrupted song motor control. I found that syllable-triggered OV stimulation in the singing bird gradually distorted and destabilized the spectral structure of the "target" syllables, and did not affect other regions of the motif that were not paired with OV stimulation. Syllable-triggered OV stimulation could induce both short- and long-term song plasticity. The short-term plasticity was manifested as spectral distortion and increased variability of the target syllables in catch trials. The long-term plasticity was manifested as permanent song changes which persisted after the cessation of OV stimulation. Both the short- and long-term effects I observed with OV stimulation resemble the effects of deafening or peripheral distortion of auditory feedback. These results point to OV as a source of singing-related auditory feedback necessary to learned vocal control.
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