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Cognitive Development in Preterm Children: Selective Deficits in Declarative Memory in Early School Age
Introduction: Evidence from behavioral studies suggests that children born preterm, compared to those born full-term, are at increased risk for cognitive impairments, including attention and memory deficits. Those often result in school failure and difficulties in daily routines. So far, however, it is unclear whether prematurity has an impact on cognition in general or on specific functions. In order to approch this question, we explored attention and memory in 8–10 year old preterm and full-term control children. Methods: Regarding attention, an auditory oddball task with standard tones, target tones, and task-irrelevant novel sounds was used to explore event related potential (ERP) correlates of top-down and of involuntary, bottom-up aspects of attention. Neuropsychological tests were administered to evaluate the functioning of specific memory systems, namely semantic memory (memory for facts), episodic memory (memory for events experienced by an individual) and working memory. In addition, an intelligence screening was used to test whether any memory impairments were independent of intelligence. To further examine whether potential memory difficulties in preterms are caused by a dysfunction of specific memory retrieval processes, we ran a recognition memory experiment with EEG recording. According to dual-process models of recognition memory, memory retrieval can be based on fast occuring and context free familiarity signals and on slower, contextual retrieval (i.e. recollection). To investigate whether preterms show changes in the ERP correlates of familiarity and recollection, preterm and full-term children first learned pictures and afterwards had to discriminate old from new pictures. Results: The oddball task experiment revealed similar target- and novelty-processing in both groups, suggesting that attentional processes are not impaired in preterms. In the neuropsychological tests, preterms had lower scores in semantic memory, but not in episodic and working memory tasks, even if controlled for intelligence. The recognition task performance showed similar memory in both groups. Regarding the ERPs, both groups showed similar correlates of familiarity. However, in preterms, there was no ERP correlate of recollection. Furthermore, in preterms, a post hoc analysis showed a positive correlation between gestational age and the magnitude of the ERP correlate of recollection. Conclusions: The maturational state of the brain at birth affects memory functions even at age 8–10. Overall, our findings suggest that preterms have no general cognitive impairment, but specifically, semantic memory and recollective processing are impaired. Therefore, besides intensive medical treatment perinatally, specific intervention strategies later targeting memory functions would be promising to minimize the long-term individual adverse cognitive effects of prematurity.