Semantic-episodic memory interactions in semantic dementia: Implications for retrograde memory function

Semantic dementia refers to a multi-modal loss of semantic knowledge, resulting from degeneration of the anterior temporal neocortex. Loss of information is not absolute. We have previously demonstrated (Snowden, Griffiths, & Neary, 1994, 1995) that autobiographical experience has an important role in influencing information preservation, and have argued that patients' preserved experiential memory helps to invest words and objects with meaning that would otherwise be lost. Those studies suggested a particularly critical role of current autobiographical experience. The present study aimed to explore the generality of the observed current information superiority in an investigation of patients' knowledge of celebrities, understanding of a contemporary and obsolete monetary system, and autobiographical memory. Performance was superior for contemporary (recent) than for past (remote) information, both factual and autobiographic, suggesting an inverse of the temporally graded pattern of retrograde memory found in classical amnesia. It is argued that the findings are consistent with explanations of the ''temporal gradient'' effect of retrograde amnesia in terms of qualitative differences in recent and remote memories. The findings indicate a bidirectional interaction between autobiographic and semantic memorising, and emphasise a continuous, dynamic interrelationship rather than a time-limited role. An important distinction is highlighted between autobiographical and impersonal episodic memory. The findings have significant theoretical implications both for the understanding of retrograde memory function and the interrelationship between episodic and semantic memory.