Figure 1.

Simplified model of efferent pathways for vocal control in humans. Brain regions are indicated in yellow when bearing reference to, or representing the emotional motor pathway, in green when being assigned to the voluntary motor pathway, and in lime-green when relating to the effectors for vocal output. The PAG is crucial for the control of emotional vocal expression via its connections with the nucleus ambiguus (laryngeal effectors) and the nucleus retroambiguus [respiratory/vocal coordination (Jurgens, 2002; Holstege and Subramanian, 2016; Belyk and Brown, 2017)]. The PAG-activity is driven by the hypothalamus, which furnishes the main input for spontaneous vocal reactions (Dujardin and Jurgens, 2006). The PAG is also a target of efferences from the ACC. The ACC is an evolutionarily older cortical site, which appears to support a directed expression of vocalization (Jurgens, 1998). In humans, the functions of the dorsal ACC include emotional intonations that are superimposed on the production of volitional speech (Barrett et al., 2004; Aziz-Zadeh et al., 2010; Belyk and Brown, 2016; Dichter et al., 2018). The AI cortex senses the current affective state and automatically relays the corresponding information to the emotional motor system (Phillips et al., 2003). The ventral laryngeal motor cortex (LMCV) is the homologue of the non-human primate LMC, whereas the dorsal laryngeal motor cortex (LMCD) is unique in the human primary motor cortex. These primary motor cortical regions extend the potential of voluntary vocal control, permitting flexible speech and song, notably via the reticular formation of the lower brainstem and by direct connections with laryngeal effectors in the nucleus ambiguus (Fitch, 2011; Simonyan and Horwitz, 2011; Belyk and Brown, 2017).