Neural Language Processing in Adolescent First-Language Learners: Longitudinal Case Studies in American Sign Language

Area of Science:

• Neurolinguistics
• Neuroscience
• Developmental Neuroscience

Background:

• The critical period hypothesis suggests early language exposure is crucial for typical neural language development.
• Investigating neural processing in individuals with late language acquisition provides insights into brain plasticity and language representation.

Observation:

• A longitudinal study examined two deaf adolescents with late exposure to American Sign Language (ASL) using anatomically constrained magnetoencephalography (aMEG).
• Initial assessments after 2-3 years of ASL showed atypical neural responses, localized to right dorsal frontoparietal regions.
• Further observation after an additional 15 months revealed persistent polarity atypicalities but evolving localization patterns.

Findings:

• Neural responses to less familiar signed words remained atypically localized.
• Responses to highly familiar signed words showed increased concentration in the left perisylvian language network.
• The findings indicate that while initial language exposure timing impacts neural organization, the brain's language networks remain adaptable into adolescence.

Implications:

• Late language acquisition demonstrates the brain's capacity for reorganization and adaptation.
• The study challenges strict critical period limitations, suggesting ongoing neural plasticity for language throughout adolescence.
• Understanding these developmental trajectories informs educational and therapeutic interventions for individuals with delayed language exposure.