Memory performance and the growth hormone/insulin-like growth factor axis in elderly: A positron emission tomography study

The relationship between the growth hormone/insulin-like growth factor (GH-IGF)-I status and memory performance is studied in 24 elderly males and females, aged 75 - 85 years. Positron emission tomography ( PET) was used to measure differences in regional cerebral blood flow during the performance of a delayed-non-match-to-sample (DNMTS) working memory task. Quality and speed of performance on the DNMTS task were measured separately for the easy items ( 3, 4 and 5 letters) and difficult items ( 6, 7 and 8 letters). Results were analyzed in two different groups based on the IGF-I level of the subjects ( low or high IGF-I). Error rates on the working memory task were not different, but the high IGF-I group had shorter reaction times on the easy items. The high IGF-I group showed a significantly greater increase in cerebral blood flow in the left premotor cortex ( easy items) and left dorsolateral prefrontal cortex ( difficult items) compared to the low IGF-I group. It is concluded that elderly with high IGF-I levels are capable of faster working memory performance and increased recruitment of task-associated prefrontal regions. Copyright (C) 2005 S. Karger AG, Basel.