Maturation of interhemispheric asymmetry of local cortical responses to abstract and concrete verbs: a magnetic mismatch negativity study

BACKGROUND: The development of neural networks that support lexico-semantic processing in children remains poorly understood. In contrast, investigations in adult subjects have provided ample evidence regarding the brain mechanisms underpinning the processing of abstract and concrete semantics. These studies have shown that interhemispheric asymmetry of neural responses across modal and amodal cortical areas diverges between these two types of semantics, with more left-lateralized networks for abstract than concrete words. Little is known about such distinctions in children; addressing this gap was the goal of the present study. AIM: We sought to investigate age-related dynamics of lateralization of neural response patterns associated with the processing of abstract and concrete semantics in children. METHODS: We used magnetoencephalography (MEG) and a mismatch negativity (MMN) paradigm which employed auditory presentation of abstract and concrete verbs. Forty-one healthy children (5-13 years old) were exposed to these stimuli presented outside the focus of attention. Source time courses of neuromagnetic activity were reconstructed using minimum-norm estimates within pre-defined regions of interest: primary auditory cortex, primary motor cortex and inferior frontal gyrus of both hemispheres. The magnitudes of responses were further compared statistically between the two hemispheres within two age groups: younger (5-9 years old) and older (10-13 years old) children. RESULTS: We observed regionally-specific differences in the lateralization of event-related MMN responses to concrete vs. abstract words in motor and inferior frontal cortical areas (paired permutation tests, p < 0.05). Moreover, these lateralization patterns changed with age, becoming less prominent in the older children. Particularly, for the concrete motor action-related verb, the right-hemispheric response decreased within the hand motor area, whereas for the abstract verb the response decrease took place within the left inferior frontal areas (BA45 and BA47). CONCLUSION: The present area- and hemisphere-specific dynamics of responses in the motor cortex and Broca’s area might be considered as a correlate of age-related changes in neurocognitive strategies for the comprehension of abstract and concrete language.