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Talk;infancy

Thursday stream 2 Session 09.00 - 11.10 Length 25 minutes

Early Brain Activation Differs In Children At Risk For Familial Dyslexia

P. H. T. Leppanen ,, T. Guttorm and H. Lyytinen

(1) Center for Molecular and Behavioral Neuroscience, Rutgers University, USA (2) Department of Psychology, University of Jyväskylä, Finland leppanen@axon.rutgers.edu

Abstract

Developmental dyslexia, a specific reading disorder, is known to run in families, but as yet, little is known of the early precursors of the disorder. At the phenotype level, poor readers differ from controls, for example, in categorising speech sound durations. These kind of phonological level problems could be linked to underlying developmental processing deficits. To test whether such processing deviations could be traced back to early development, we have mapped auditory ERPs from newborns and six-month-old infants participating in the Jyväskylä Longitudinal Study of Dyslexia (JLD). The half of the infants were from families with at least one dyslexic parent and familial background of dyslexia (at risk group) and the other half from matched control families (control group). We review here data measured in 3 experimental conditions: 1) consonant-vowel (CV) syllables (ba, da, ga, paa, taa, kaa, ka) presented with equal probability (newborns). All other sounds were presented in oddball paradigms, in which rare deviant stimuli, embedded among frequent standards, typically elicit a mismatch negativity (MMN) component thought to reflect pre-attentive sound change detection. The second (2) condition involved syllables with a change in vowel duration (kaa vs. ka; newborns and six-month-olds) and the third (3) pseudo-words with a change in consonant duration (ata vs. 2 variants of atta; six-month-olds). ERPs indicated that both at-risk and control infants discriminate passively between presented speech stimuli. However, at birth, the ERP scalp distribution for the CV syllables differed between the at-risk and control groups. Also, ERPs to rare short ka stimuli were different at birth between the groups when an appropriate presentation rate was used. At the age of six months, most marked group differences were found in the ERP amplitude and scalp distribution for a consonant duration change (ata vs. atta). In particular, a late component related in part to the detection of the changes in the temporal sound pattern was smaller in the at-risk group but selectively at the left hemisphere. These differences could be related to differences in temporal integration and timing of auditory/speech information and the brain's less efficient ability to form adequate representations of the ongoing sound stream in the at-risk group. Overall, individuals affected by dyslexia may have a very early auditory/speech perceptual problem contributing, in turn, to the development of difficulties in phonological processing. Discovery of such an early precursor might enable to start intervention and remediation during the most critical periods of early language development.