Fig. 7: A conserved midbrain periaqueductal gray (PAG) node for social context-specific vocalisation.

a Sagittal brain drawing for midshipman fish summarises proposed roles of the caudal superficial (cs) and deep (cd) PAG zones in generating social context-specific vocal output (current study), and how hindbrain-spinal vocal prepacemaker (VPP), pacemaker (VPN), and motor (VMN) nuclei shape acoustic features of grunts (see ⁴⁵). b PAG stimulation via glutamate or excitatory amino acids leads to vocal output in fish (current study) and mammals (see Discussion). Schematic drawing of proposal that the PAG activates one or more hindbrain-spinal motor populations driving vocalisation, including those for respiration, a major character distinguishing mammals from fishes given the dependence of vocalisation among most tetrapods on respiration. Hindbrain-spinal motor populations in toadfishes (e.g., midshipman fish) and mammals (e.g., see^56,73) are proposed to refine the properties of clade- or species-typical basic acoustic unit(s), with the PAG selectively reconfiguring the output of one or more units to determine the temporal features of different context-specific vocalisations.