The relevance of the unique anatomy of the human prefrontal operculum to the emergence of speech

Journal article

Speech perception and production are fundamental to human communication. Many models have been proposed to explain these processes. However, one drawback of these models is that they generally fail to consider the mechanisms shared between the two, partly due to ongoing debates about the extent of their shared resources. Some theories propose interdependence, while others suggest interconnected networks. The prevailing view in the literature is that these functions share mechanisms, with speech production contributing to perception in a context-dependent way. This thesis investigates two hypotheses: first, that motor representations support speech perception, particularly in challenging listening conditions, by resolving ambiguous signals; and second, that the speech-motor system plays a broader role in phonological processing beyond challenging contexts. In the first study, I conducted a neuroimaging meta-analysis to examine whether brain regions associated with speech production overlap with those involved in challenging speech perception, and how this overlap varies across listening conditions. Findings revealed both context-dependent and context-independent overlaps, primarily in sensorimotor and higher-order cognitive regions, rather than in core speech-motor areas. This suggests that while shared mechanisms do exist, the core speech-motor regions may not play a compensatory role in perception. In the second study, I used magnetoencephalography to explore the involvement of the speech-motor system in phonological discrimination under different noise levels. Results showed simultaneous activity in the posterior superior temporal gyrus and ventral primary motor cortex during phonological discrimination, regardless of noise conditions. This supports the second hypothesis, showing that the speech-motor system engages in phonological processing regardless of listening challenges. In the third study, I demonstrated that repeating syllables aloud before syllable discrimination in noise improved perceptual performance, further supporting the speech-motor system's role in phonological processing. Altogether, these results challenge the idea that the speech-motor system is primarily compensatory and suggest that it plays a more integral role in phonological processing. The implications of these findings are discussed in the context of current models of speech processing, and a new model is proposed that incorporates auditory, cognitive, and motor processes shared between perception and production. This thesis provides a better understanding of the complex relationship between speech perception and production.Ph.D

Authors: Amiez, C; Verstraete, C; Sallet, J; Hadj-Bouziane, F; Ben Hamed, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Nature Research
• Journal: Communications Biology
• Volume: 6
• Issue: 1
• Pages: 693-693
• Article number: 693
• Publication date: 2023-07-05
• DOI: 10.1038/s42003-023-05066-9
• EISSN: 2399-3642
• ISSN: 2399-3642
• Language: English
• Keywords: Operculum (bryozoa); Ventrolateral prefrontal cortex; Human brain; Biology; Psychology; Neuroanatomy; Ventromedial prefrontal cortex; Neuroscience; Broca's area; Prefrontal cortex; Cognition; Cognitive psychology