Date of Award
2026
Document Type
Thesis
Degree Name
Doctor of Philosophy (PhD)
Thesis Advisor
Erich D. Jarvis
Abstract
Vocal communication is used to transmit a range of information to other individuals. While many vocalizations are innate, some species can learn to change their vocal output. This is termed vocal-learning, and it is a rare trait and a necessary building block for human spoken language and songbird song. Comparative work in humans and songbirds suggests that convergent genetic and neural specializations may drive these learned vocal behaviors. Two key features of these advanced vocal learners are: i) specialized primary motor regions in the forebrain with activity tied to vocalization; and ii) dense monosynaptic projections from the primary motor cortex to brainstem vocal motor neurons. Work from our lab suggests that the mouse ultrasonic vocalization (USV) system has some features similar to those found in advanced vocal learners. USV production is innate, but mice show context-dependent changes in their syllable repertoire. Mice may also possess a rudimentary laryngeal motor cortex (LMC), with a sparse direct projection to laryngeal motor neurons in the nucleus ambiguus (Amb) and sparse populations with short-latency functional control over vocal musculature. Prior to these studies, mice have been assumed to lack any cortical involvement in the production of ultrasonic vocalizations. The limited behavioral flexibility of mouse song and evidence of forebrain representations of vocal muscles suggest that vocal learning may exist over a continuum, with mice being at the limited end of the continuum, able to exert some cortical control over USV production. This hypothesis argues that vocal learning is not an all-or-nothing ability, but exists on a continuous range of vocal behavior, supported by a corresponding range of neural and genetic specializations. In this thesis, I proposed to test the continuum hypothesis, by investigating whether there is a role of primary motor cortex in mouse vocal behavior. I first characterized the role of the sparse direct projection in the control of vocal muscles. I used replication-deficient rabies tracing to confirm that there is a sparse projection from layer 5 neurons of LMC to brainstem laryngeal motor neurons, and also found that an anterior M1 region, orofacial motor cortex (OMC), also has a direct cortico-motoneuronal projection. I then used PLXNA1fl/fl;RBP4-CRE transgenic mice, which have denser innervation from the cortex to Amb, to test the functional consequences of enhancement of this circuit. I used paired intracortical microstimulation (ICMS) and electromyography (EMG) and found faster responses in the larynx of these mice to cortical stimulations. These findings show that the enhancement of direct cortico-motoneuronal projections produce faster cortical control over vocal muscles. I then tested whether mouse M1 has any neural activity associated with vocalization behavior. I combined electrophysiological recordings in LMC and OMC with video and audio monitoring of freely behaving and vocalizing males. I identified sparse populations of neurons with activity modulated over the production of bouts of USVs. This is the first report of vocalization-related activity in mouse M1. Finally, I developed a novel method to identify individual USV sources in pairs of vocalizing mice. This method used wearable miniature microphones to detect and assign USVs to a single animal based on simple amplitude differences. I reliably identified the individual responsible for the vocalization, and found that female mice produce far fewer USVs in a male- female pair than previously assumed. This method allows further study of the inter-individual vocal dynamics and behavior during the production of social USV. Overall, my findings support the continuum hypothesis of vocal learning. The direct cortical input from M1 to laryngeal motor neurons appears to be an evolutionary node to have faster control of vocal musculature. These same M1 regions have limited but present populations with vocalization-associated activity. This suggests that a sparse cortical representation for vocal muscles may be conserved. These results provide greater insight into the cortical control of vocalization in the mammalian brain and the evolution of more advanced vocal learning.
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Recommended Citation
Waidmann, Elena N. Duryea, "Investigating Primary Motor Cortex Involvement in Mouse Vocal Communication" (2026). Student Theses and Dissertations. 866.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/866
Comments
A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy