HM, word knowledge, and aging: Support for a new theory of long-term retrograde amnesia

This study develops a new theory of long-term retrograde amnesia that encom passes episodic and semantic memory, including word knowledge. Under the th eory, retrograde amnesia in both normal individuals and hippocampal amnesic s reflects transmission deficits caused by aging, nonrecent use of connecti ons, and infrequent use of connections over the life span. However, transmi ssion deficits cause severe and irreversible retrograde amnesia only in amn esics who (unlike normal persons) cannot readily form new connections to re place nonfunctioning ones. The results of this study are consistent with th is theory: For low-frequency but not high-frequency words, a famous "hippoc ampal amnesic" (H.M.) at age 71 performed worse than memory-normal control participants in a lexical decision experiment and a meaning-definition task (e.g., What does squander mean?). Also as predicted, H.M.'s lexical decisi on performance declined dramatically between ages 57 and 71 for low-frequen cy words, but was age invariant for high-frequency words.