Integration of faces and vocalizations in ventral prefrontal cortex: Implications for the evolution of audiovisual speech

Abstract

The integration of facial gestures and vocal signals is an essential process in human communication and relies on an interconnected circuit of brain regions, including language regions in the inferior frontal gyrus (IFG). Studies have determined that ventral prefrontal cortical regions in macaques [e.g., the ventrolateral prefrontal cortex (VLPFC)] share similar cytoarchitectonic features as cortical areas in the human IFG, suggesting structural homology. Anterograde and retrograde tracing studies show that macaque VLPFC receives afferents from the superior and inferior temporal gyrus, which provide complex auditory and visual information, respectively. Moreover, physiological studies have shown that single neurons in VLPFC integrate species-specific face and vocal stimuli. Although bimodal responses may be found across a wide region of prefrontal cortex, vocalization responsive cells, which also respond to faces, are mainly found in anterior VLPFC. This suggests that VLPFC may be specialized to process and integrate social communication information, just as the IFG is specialized to process and integrate speech and gestures in the human brain.frontal lobe | sensory integration | primate | neurophysiology

Hemispheric association and dissociation of voice and speech information processing in stroke

“…This difficulty was not related to the absence of pitch information since their pitch perception threshold did not differ from other patient groups. It has been proposed that the right IFG plays a general role in voice recognition and social communication at large, since direct connections have been demonstrated between the STG and the ventrolateral prefrontal cortex of the macaque (equivalent of IFG in humans) along with vocalization responsive cells (Romanski, 2012). Voice deficits observed here following right IFG lesions, often in association with insula lesions (although the association was not significant), could then reflect a disconnection syndrome from the STS.…”

Single neurons in monkey prefrontal cortex encode volitional initiation of vocalizations

“…BA 44/45 shows anatomical similarities, comparable cytoarchitectonics 24 as well as similar cortico-cortical projections as Broca's area 24 . Therefore, these areas would be ideally situated to control audio-vocal behaviour 34 because they are tuned to species-specific auditory input 28,30 , synthesize multimodal social information 35,36 and generate orofacial motor output 25 . Nevertheless, a few studies report that bilateral damage to the ventrolateral frontal cortices has no significant effect on vocal behaviour in rhesus macaques 8,10 .…”

Using naturalistic utterances to investigate vocal communication processing and development in human and non-human primates

“…They found multisensory neurons in the rhesus macaque vlPFC that exhibited enhancement or suppression in response to the presentation of face/vocalization stimuli. Romanski (2012) has proposed that the integration of vocalizations and faces that occurs in the macaque prefrontal cortex may represent an evolutionary precursor to the processing of multisensory linguistic input in the frontal lobe of the human brain (Romanski, 2012). …”