Neural Representation of the Coding of Language and Speech in Children with Congenital Toxoplasmosis

Purpose: Children diagnosed with congenital toxoplasmosis (CT) are at increased risk of central auditory nervous system dysfunction, potentially affecting their hearing skills and language development, even in the absence of direct hearing loss. This study therefore explored whether electrophysiological measures of language and speech were affected in children with CT. Method: This prospective longitudinal cohort study recruited 13 children diagnosed with CT (the CT group) and 25 typically developing children (control group). Participants underwent frequency-following response (FFR) recording at three developmental stages: stage 1 (S1) covering the first to third month of life; stage 2 (S2) spanning the sixth to tenth month; and finally stage 3 (S3) from 4 to 6 years, although by then losses to follow-up were severe (>50%). During S3, language and speech development assessments were also conducted. Results: Logistic regression between FFR components and expressive language assessments showed no significant differences, although statistical power was compromised by the small number of remaining children. There was no significant interaction between the FFR components across the stages or between groups (p > 0.05). Main-effect analyses revealed that children with congenital toxoplasmosis exhibited significantly prolonged latencies relative to controls for waves A (β = 0.38 ms, 95% CI [0.11, 0.65], p = 0.008), F (β = 0.46 ms, 95% CI [0.01, 0.91], p = 0.048), and O (β = 0.87 ms, 95% CI [0.40, 1.34], p < 0.001). Conclusions: Our findings indicate that children diagnosed with CT exhibit prolonged latencies of waves A, F, and O and reduced slope values in the FFR, suggesting impairments in neural speech sound coding from the first months of life into early childhood, independent of the assessment stage. Although FFR latencies did not predict expressive language outcomes, all children in the CT group assessed at S3 presented language and/or speech alterations, which suggests a possible association between congenital toxoplasmosis and speech development. Given the small number of children assessed at this stage, this is a preliminary finding that warrants further investigation in larger longitudinal studies.