Oscillatory gamma activity mediates the pathway from socioeconomic status to language acquisition in infancy

Background: The predictable path to child language acquisition is largely constrained by both brain maturation and environmental experience. The synchronized activity of large numbers of neurons gives rise to macroscopic brain oscillations on an electroencephalogram (EEG). It has been found that neural oscillations at rest in the gamma frequency band (25-45 Hz) are associated with development of different cognitive systems, including language. Although the etiology of language is explained by genetically driven brain maturation factors, environment plays a significant role. Specifically, candidate pathways from environment to language development include sociodemographic factors, primarily socioeconomic status (SES) which is likely to exert its effects on language development through other factors, such as parenting style. Despite these assumptions, no studies have so far examined the interrelation between brain maturation factors such as gamma frequency oscillatory activity, environmental factors such as SES, and language acquisition.

Aim and method: In a longitudinal study of 84 Italian typically developing infants, we measured the power of oscillatory gamma activity as mediator between SES and language acquisition. Baseline EEG and information about SES were collected when infants were aged 6 months. Children were followed-up longitudinally to measure expressive vocabulary and Mean Length of Utterance (MLU) at 24 months.

Results: The mediation model showed that SES is associated with gamma power which, in turn, is associated with expressive language at age 24 months. A higher SES predicted an increase in left central gamma power which, in turn, predicted better language scores.

Conclusions: These results confirm the predictive role of gamma activity oscillatory activity on later language acquisition, suggesting a specific role for these oscillatory mechanisms in language development milestones such as vocabulary development and early word combination. Furthermore, they suggest that SES differences in brain activity may be apparent at early stages of life and affect later language skills. If replicated, our findings could contribute to identifying highest-risk children and may prompt cost-effective preventive/treatment strategies.