The effects of age on the neural correlates of episodic encoding

Young and old adults underwent positron emission tomographic scans while en coding pictures of objects and wards using three encoding strategies: deep processing (a semantic living/nonliving judgement), shallow processing (siz e judgement) and intentional learning. Picture memory exceeded word memory in both young and old groups, and there was an age-related decrement only i n word recognition. During the encoding tasks three brain activity patterns were found that differentiated stimulus type and the different encoding st rategies. The stimulus-specific pattern was characterized by greater activi ty in extrastriate and medial temporal cortices during picture encoding, an d greater activity in left prefrontal and temporal cortices during encoding of words. The older adults showed this pattern to a significantly lesser d egree. A pattern distinguishing deep processing from intentional learning o f words and pictures was identified, characterized mainly by differences in prefrontal cortex, and this pattern also was of significantly lesser magni tude in the old group. A final pattern identified areas with increased acti vity during deep processing and intentional learning of pictures, including left prefrontal and bilateral medial temporal regions. There was no group difference in this pattern. These results indicate age-related dysfunction in several encoding networks, with sparing of one specifically invoked in m ore elaborate encoding of pictures. These age-related changes appear to aff ect verbal memory more than picture memory.