Healthy aging is associated with a heterogeneous decline across cognitive functions, typically observed in language performances. Examining resting-state fMRI and neuropsychological data from 628 healthy adults (age 18-88) from the CamCAN cohort, we performed state-of-the-art graph theoretical analysis to uncover the neural mechanisms underlying this cognitive variability. At the cognitive level, our findings suggest that language processing is not an isolated function but is modulated throughout an individual's lifespan by the extent of inter-cognitive synergy between language, long-term memory, and executive functions. At the cerebral level, we show that the coupling between DMN (Default Mode Network) and FPN (Fronto-Parietal Network) regions may be the way for the brain to compensate for the effects of dedifferentiation at a minimal cost, efficiently mitigating the age-related cognitive decline in language production, fluid processing, and verbal fluency. Notably, the dynamic of cognitive resilience provided by this synergistic coupling seems to follow the Seneca effect typically found in complex systems: a slow rise followed by an abrupt decline. Specifically, we argue that reducing the DMN-FPN coupling could trigger accelerated cognitive decline around age 50. We summarize our findings in a novel SENECA model (Synergistic, Economical, Nonlinear, Emergent, Cognitive Aging), integrating connectomic and cognitive perspectives within a complex system perspective. Our study furthers our understanding of the dedifferentiation-compensation mechanisms that uphold inter-cognitive functioning during healthy aging and suggests that the fifth decade of life could transition towards less synergistic processing.
Introduction: Orofacial somatosensory inputs modify the perception of speech sounds. Such auditory-somatosensory integration likely develops alongside speech production acquisition. We examined whether the somatosensory effect in speech perception varies depending on individual characteristics of speech production.Methods: The somatosensory effect in speech perception was assessed by changes in category boundary between /e/ and /ø/ in a vowel identification test resulting from somatosensory stimulation providing facial skin deformation in the rearward direction corresponding to articulatory movement for /e/ applied together with the auditory input. Speech production performance was quantified by the acoustic distances between the average first, second and third formants of /e/ and /ø/ utterances recorded in a separate test.Results: The category boundary between /e/ and /ø/ was significantly shifted towards /ø/ due to the somatosensory stimulation as in Trudeau-Fisette et al. (2019). The amplitude of the category boundary shift was significantly correlated with the acoustic distance between the mean second -and marginally thirdformants of /e/ and /ø/ productions, with no correlation with the first formant distance.Discussion: Greater acoustic distances can be related to larger contrasts between the articulatory targets of vowels in speech production. These results suggest that the somatosensory effect in speech perception can be linked to speech production performance.
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