Spatial memory abilities and abnormal development of the hippocampal formation in Down syndrome.

The recent evidence concerning the nature of cognitive development in Down Syndrome (DS) suggests that it is different than normal development. The neuropathology seen in DS implicates a prenatal interruption of normal neural development as a possible basis for these differences. Since the hippocampal formation (HF) undergoes extensive postnatal maturation and is found to be abnormal in DS, it is proposed that cognitive deficits associated with DS would be most evident in tasks requiring hippocampal function. The performance of DS children at 16-18 months and 28-30 months of age was compared to that of age-matched control groups of normal children on two cognitive tasks requiring abilities that develop during the first postnatal year shown not to involve hippocampal function, and a task requiring abilities that develop during the second postnatal year shown to require hippocampal functioning. The results show that the DS performed comparably on the nonhippocampal tasks but differently on the hippocampal task. The normal children's performance supports the position that the ability to perform HF tasks develops during the second postnatal year while the performance of the older DS children suggested that this development does not occur in DS. The specificity of the deficits to the hippocampal task was interpreted as indicative of a lack of HF development in DS