Aging patterns of Japanese auditory semantic processing: an fMRI study.

The efficacy of listening comprehension is presumably sustained over the life span, contradicting the stereotype of universal cognitive decline. It is thus worth investigating whether and how the preserved auditory semantic function is supported by affected or unaffected neural mechanism with age. To investigate this issue, 22 younger and 21 older Japanese adults were imaged in a 3 Tesla MRI scanner while performing an auditory semantic-tone task. Results showed that (a) relative to younger adults, older participants had preserved accuracy and slowed responses, underpinned by weakened interconnectivity and largely unchanged activation and laterality; (b) older adults with superior performance developed increased regional left-lateralization and stronger interregional connectivity within the domain-general networks; (c) these age-related or performance-related cortical reorganizations were largely consistent with neurocognitive aging models that were supported by age-sensitive cognitive domains, suggesting that these models might also be accountable for relatively age-intact cognitive functions such as auditory semantic processing.

The Neural Correlates of Spoken Sentence Comprehension in the Chinese Language: An fMRI Study.

PURPOSE: Everyday social communication emphasizes speech comprehension. To date, most neurobiological models regarding auditory semantic processing are based on alphabetic languages, where the character-based languages such as Chinese are largely underrepresented. Thus, the current study attempted to investigate the neural network of speech comprehension specifically for the Chinese language. METHODS: Twenty-two native Mandarin Chinese speakers were imaged while performing a passive listening task of forward and backward sentences. Sentences were used as task stimuli, as sentences compared with words were more frequently utilized in daily speech comprehension. RESULTS: Our results suggested that spoken Chinese sentence comprehension may involve a neural network comprising the left middle temporal gyrus, the left anterior temporal lobe, and the bilateral posterior superior temporal lobes. The occipitotemporal visual cortex was not found to be significantly involved with the sentence-level network of spoken Chinese comprehension, as bottom-up visualization process from homophones to visual forms may be less needed due to the availability of top-down contextual controls in sentence processing. In addition, no significant functional connectivity was observed, likely obscured by the low cognitive demand of the task conditions. Limitations and future directions were discussed. CONCLUSION: The current Chinese network seems to largely resemble the auditory semantic network for alphabetic languages but with features specific to Chinese. While the left inferior parietal lobule in the dorsal stream may have little involvement in the listening comprehension of Chinese sentences, the ventral neural stream via the temporal cortex appears to be more emphasized. The current findings deepen our understanding of how the semantic nature of spoken Chinese sentences influences the neural mechanism engaged.

L1 and L2 processing in the bilingual brain: A meta-analysis of neuroimaging studies.

Neuroimaging studies investigating bilingual processes have produced controversial results in determining similarities versus differences between L1 and L2 neural networks. The current meta-analytic study was conducted to examine what factors play a role in the similarities and differences between L1 and L2 networks with a focus on age of acquisition (AOA) and whether the orthographic transparency of L2 is more or less transparent than that of L1. Using activation likelihood estimation (ALE), we found L2 processing involved more additional regions than L1 for late bilinguals in comparison to early bilinguals, suggesting L2 processing is more demanding in late bilinguals. We also provide direct evidence that AOA of L2 influences L1 processing through the findings that early bilinguals had greater activation in the left fusiform gyrus than late bilinguals during L1 processing even when L1 languages were the same in the two groups, presumably due to greater co-activation of orthography in L1 and L2 in early bilinguals. In addition, we found that the same L2 languages evoked different brain activation patterns depending on whether it was more or less transparent than L1 in orthographic transparency. The bilateral auditory cortex and right precentral gyrus were more involved in shallower-than-L1 L2s, suggesting a "sound-out" strategy for a more regular language by involving the phonological regions and sensorimotor regions to a greater degree. In contrast, the left frontal cortex was more involved in the processing of deeper-than-L1 L2s, presumably due to the increased arbitrariness of mapping between orthography and phonology in L2.