The vocal-motor system of the human brain

Abstract

The larynx is the mammalian organ of vocalization. Humans have a degree of control over this organ considerably beyond the abilities of other primates, most notably in our control over the larynx during speech. Although there is an abundance of research on the neural basis of speech, relatively little of this research has focused on the control of the larynx. First, I performed a meta-analysis to search for brain areas responsible for making explicit judgments about affective prosody to identify candidate premotor areas in prefrontal cortex that may also plan the affective component of affective prosody (Chapter 2). The inferior frontal gyrus pars orbitalis was the only prefrontal region preferentially engaged by affective vocalizations. Second, I used functional magnetic resonance imaging to determine whether there are discrete neural systems for producing innate-affective versus arbitrary non-affective vocalizations in the human brain, as has been predicted from non-human primate models (Chapter 3). The vocal-motor system demonstrated a lack of specialization since both types of vocalizations engaged the entire network. Third, I searched for brain areas that were preferentially engaged during vocal imitation (Chapter 4), which is a key process in vocal learning. Vocal imitation preferentially engaged a cortico-striate network similar to that predicted from avian models of vocal imitation. Finally, I performed a meta-analysis to explore the neural basis of persistent developmental stuttering (Chapter 5), a speech disorder that is associated with poor control of the laryngeal muscles. Among other brain areas, primary motor regions controlling the larynx were abnormally activated in the brains of people who stutter. Together these studies advance our knowledge of the human vocal-motor system, how it relates to that in other species, and how this system may be disrupted in persistent developmental stuttering. I discuss remaining gaps in our knowledge that will be the focus of my future research.