Data from: Vocal repertoire expansion in singing mice by co-opting a conserved midbrain circuit node

How neural circuits generate diverse behaviors is a fundamental question
in neuroscience. Distinct behavioral outputs may arise from either
dedicated motor circuits or shared circuits operating in different
functional states. While multifunctional circuits offer an efficient
solution for behavioral flexibility and may drive rapid evolutionary
adaptations, their neural mechanisms remain poorly understood, especially
in mammals. Here, we leverage the rich vocal repertoire of the singing
mouse (Scotinomys teguina) to investigate the organizational logic of
multifunctional motor circuits. We developed a behavioral assay (PAIRId)
that enables precise attribution of vocalizations during social
interactions. This paradigm revealed two distinct vocal modes: soft,
variable, ultrasonic vocalizations (USVs) ancestral to rodents used for
short-range communication, and loud, rhythmic, human-audible songs unique
to the singing mouse lineage used for long-range communication. Despite
their substantial acoustic and contextual differences, we found that USVs
and songs do not arise from parallel pathways. Instead, they share the
same sound production mechanism, phonatory-respiratory coupling, and vocal
gating from the midbrain caudolateral periaqueductal gray (clPAG). To
understand the mechanism governing song production, we combined
mathematical modeling of song rhythm with synaptic silencing of clPAG,
which progressively reduced song amplitude and duration. We demonstrate
that song duration decreases via a single parameter controlling its
termination. Notably, this mechanism also accounts for sexual dimorphism
in songs, identifying clPAG as a key locus for driving natural behavioral
variability. Our findings reveal how parametric tuning of a central
circuit node produces distinct vocal modes, providing a mechanistic basis
for rapid behavioral evolution in mammals.