The disparate effects of Alzheimer's disease and Huntington's disease on semantic memory

Alzheimer's disease (AD) and Huntington's disease (HD) impair performance o n semantic memory tasks, but researchers disagree on whether AD and HD caus e these impairments in the same manner. According to one view, AD disrupts the storage of semantic memories, whereas HD disrupts the retrieval of sema ntic memories. Dissenters argue that AD, like HD, disrupts retrieval. In th is study, participants generated category exemplars (e.g., kinds of fruits) for 1 min, and response latencies were examined. Relative to healthy contr ols, the 12 AD patients produced a larger proportion of responses earlier i n the recall period, consistent with the view that AD patients quickly exha ust their limited supply of items in storage. By contrast, the 12 HD patien ts produced a larger proportion of their responses late in the recall perio d, consistent with the view that HD slows retrieval.