Age-Related Differences in Speech and Gray Matter Volume: The Modulating Role of Multilingualism

Speech involves complex processes such as language formulation, motor coordination, and cognitive functions. As people age, their speech abilities often decline, showing reduced fluency and complexity. Older adults also show decreased gray matter volume. However, the relationship between age-related differences in speech and gray matter volume remain unclear. Multilinguals may exhibit unique age-related speech patterns depending on their language profiles. This study investigates the relationships between age-related differences in brain structure and multilingual speech across different languages, considering the effects of multilingual experience. An integrated measure of speech was calculated and used to reflect the overall speech quality, which was lower in older than younger adults. Native language speech (i.e., Cantonese) was better than non-native language speech (i.e., Mandarin), especially in older adults. More extensive use of multiple languages was associated with enhanced speech quality in both native and non-native languages. Age significantly impacts whole brain gray matter volume, which was lower in older than younger adults. The right middle temporal gyrus emerged as a critical region for speech in both languages in older adults. Bilateral putamen shows sensitivity to the effect of multilingual experience on speech performance in older adults. These findings underscore the complex interplay between age, multilingualism, and brain structure, providing valuable insights into the neural mechanisms underlying multilingual speech performance.