EVENT-RELATED BRAIN POTENTIALS DURING AN EXTENDED VISUAL RECOGNITION MEMORY TASK DEPICT DELAYED DEVELOPMENT OF CEREBRAL INHIBITORY PROCESSES AMONG 6-MONTH-OLD INFANTS WITH DOWN-SYNDROME

Development of cerebral inhibitory processes among individuals with Do wn syndrome (DS) may be delayed at an early age. In support of this hy pothesis, sensory-evoked potentials (EPs) and event-related brain pote ntials (ERPs) have previously delineated altered habituation to stimul i among infants with DS. The purpose of the current study was to provi de extended experience with visual stimuli among 6-month-old infants w ith and without DS (nDS) to determine if altered ERP and behavioral re sponse decrements would be evident even after repeated presentations o f stimuli. An 80/20% oddball paradigm was employed. Infants with DS an d nDS were matched according to age and gender. Infants with DS demons trated significantly larger Nc areas, Nc peak amplitudes, Nc2 areas an d, inversely, significantly smaller peak Pb amplitudes when compared t o infants nDS. Contrasts of the two study groups were most robust with in ERP measures from frontal (Fz) and parietal (Pz) recording sites. I nfants with DS also demonstrated a significantly slower decrement of m ost ERP components with repetitive stimulus experience. Most noteworth y was the observation of little or no decrement of ERP components at F z among infants with DS. Both infants with DS and nDS demonstrated sig nificantly larger Nc peak amplitudes, Nc areas, Nc2 areas, Pb peak amp litudes and NSW areas to rare stimuli. While significant probability a nd experiential trends were observed in visual fixation measures acros s both study groups, there were no significant differences of visual a ttention between infants with DS or nDS. These data demonstrate the va lue of ERPs within the study of atypical cognitive development during infancy and support the concept of altered inhibitory processes in the brain of infants with DS. (C) 1998 Elsevier Science B.V.