Impact of semantic and autobiographical memory on aging: The temporal gradient for famous people

The process of recognizing and identifying a familiar person (face or name) represents a basic and important activity of daily social interaction. The distinction between semantic and episodic memory has played a critical role in the attempts to understand the neurobiological basis of long term memory processes. Studies have employed designs using famous names/faces from different time epochs to help understand memory processes.;Temporal Gradient (TG) refers to the notion that recent memories are more vulnerable to the effects of brain damage than are older memories. Studies of the nature of the TG make a basic distinction between semantic memory (SM) and episodic autobiographical memory (AM). However, the effect of age on the TG for both SM and AM has not been extensively studied. Understanding the nature of the temporal gradient is both of clinical and theoretical importance.;First, temporally graded remote memory impairment is seen in patient groups with a variety of neuropathological lesions. Our group is interested in examining healthy aging and pathological aging via Mild Cognitive Impairment (MCI) patients. Second, examination of the temporal gradient may help to differentiate the two main models of memory consolidation, (1) Multiple Trace Theory and (2) Hippocampal Consolidation Model, by examining the role of the hippocampal complex and neocortical areas during recall of information from different time epochs. The review of the literature to date across human lesion studies, functional imaging, and animal studies indicates mixed findings regarding the temporal gradient in relation to the HC and MTT models. Westmacott and colleagues have suggested that autobiographical significance adds the presence of an episodic component to semantic memory which impacts semantic memory performance for famous people. However, they did not examine these findings in relation to the temporal gradient.;The current study sought to build on previous findings by incorporating the concept of autobiographical significance and episodic memory into the investigation of semantic memory across time epoch (Enduring, Recent, Remote) across healthy aging (young and older adults) and MCI patients. We were also interested in examining the temporal gradient and models of memory consolidation for these three different groups.;Sixteen healthy young adults, sixteen healthy older adults, and sixteen Mild Cognitive Impairment patients completed neuropsychological measures, a famous names semantic memory test battery, and an autobiographical knowledge questionnaire. As expected, our findings showed that the healthy older adult group and MCI patients displayed the "typical" TG pattern (remote better than recent) while the younger group showed a "reversed" TG (recent better than enduring) for both semantic knowledge and autobiographical retrieval of famous names. However, we did not find that age of memory was able to differentiate the healthy older adult group from the MCI patients. The MCI patients did perform slower and less accurately than the healthy older adults across all measures and time epochs of semantic and autobiographical memory measures. We also found autobiographical and semantic knowledge to be significantly correlated for most tasks and time epochs when the groups were examined together. Lastly, we found that performance on the famous names tasks improved with better performance on episodic memory tasks, but there was not a consistent pattern across groups or time epoch. Unfortunately, our mixed findings do not help differentiate the models of semantic memory processing (HC or MTT), nor does the temporal gradient for autobiographical knowledge help differentiate healthy aging from MCI.