Two different motor systems are needed to generate human speech

Abstract

Vocalizations such as mews and cries in cats or crying and laughter in humans are examples of expression of emotions. These vocalizations are generated by the emotional motor system, in which the mesencephalic periaqueductal gray (PAG) plays a central role, as demonstrated by the fact that lesions in the PAG lead to complete mutism in cats, monkeys, as well as in humans. The PAG receives strong projections from higher limbic regions and from the anterior cingulate, insula, and orbitofrontal cortical areas. In turn, the PAG has strong access to the caudal medullary nucleus retroambiguus (NRA). The NRA is the only cell group that has direct access to the motoneurons involved in vocalization, i.e., the motoneuronal cell groups innervating soft palate, pharynx, and larynx as well as diaphragm, intercostal, abdominal, and pelvic floor muscles. Together they determine the intraabdominal, intrathoracic, and subglottic pressure, control of which is necessary for generating vocalization. Only humans can speak, because, via the lateral component of the volitional or somatic motor system, they are able to modulate vocalization into words and sentences. For this modulation they use their motor cortex, which, via its corticobulbar fibers, has direct access to the motoneurons innervating the muscles of face, mouth, tongue, larynx, and pharynx. In conclusion, humans generate speech by activating two motor systems. They generate vocalization by activating the prefrontal-PAG-NRA-motoneuronal pathway, and, at the same time, they modulate this vocalization into words and sentences by activating the corticobulbar fibers to the face, mouth, tongue, larynx, and pharynx motoneurons.

Genetic identification of a hindbrain nucleus essential for innate vocalization

“…The periaqueductal gray has been discussed as a gating center for vocal behavior but has no direct connections with motor neurons (7), and as such it depends on other premotor neurons to control vocalization. The nucleus retroambiguus, a loose neuronal cluster located posterior to the nucleus ambiguus, has been proposed to serve this role (23). Our work reveals that the NTS, like the nucleus retroambiguus with which it is reciprocally connected, projects to and entrains expiratory and laryngeal motor neurons.…”

“…S5 D-G). Among these, the ambiguus, retroambiguus, parabrachial, and periaqueductal gray nuclei have been implicated in controlling vocalization in mammals (4,23).…”

From where to what: A neuroanatomically based evolutionary model of the emergence of speech in humans

“…In contrast to most calls, which are produced in limbic regions (Holstege et al, 2015), the IFG appears involved in the emission of contact calls. A study that recorded neural activity from the IFG of macaques reported of neural discharge prior to cued or spontaneous contact call production (coo calls), but not prior to production of vocalizations-like facial movements (i.e., silent vocalizations; Coudé et al, 2011; see also Gemba et al, 1999 for similar results).…”

Електроміографічна Діагностика Порушень Моторики Язика Неврологічного Генезу У Пацієнтів З Оклюзійною Патологією

“…Розлади моторики язика, що зустрічаються у практиці лікарів-неврологів, є наслідком великої кількості різноманітних патологій [1,2]. Такі роз-лади часто мають різноманітний етіопатогенез і потребують диференційованих підходів до їх діа-гностики та лікування [3].…”