Distinct patterns and predictive values of semantic memory deterioration among individuals with prodromal Alzheimer's disease

Neuropathological evidence suggests that semantic memory deterioration can occur earlier than episodic memory in the disease progression of Alzheimer’s disease (AD). Increasing evidence has suggested marked semantic memory impairment in patients with amnestic mild cognitive impairment (aMCI-sd). However, the predicative power of semantic memory on conversion from aMCI to dementia of the Alzheimer’s type (DAT) has remained inconsistent. In addition, no studies have directly investigated semantic memory among individuals with subjective memory decline (SMD). This study aimed to investigate various aspects of semantic memory decline among aMCI patients, to evaluate the predictive values of these aspects of semantic memory on conversion to DAT, and to examine the semantic aspect of memory among SMD individuals. Individuals with SMD and patients with aMCI-single domain (aMCI-sd) suffered from disproportionately impaired performance on effortful and strategic retrieval of semantic memory, whereas those with aMCI-multiple domain (aMCI-md) suffered from deficits in both effortful and automatic retrieval of semantic memory. The conversion from aMCI-sd to DAT was predicted by poor performance in effortful retrieval of semantic memory. In contrast, conversion from aMCI-md to DAT was predicted by poor performance on automatic retrieval. These findings suggest distinctive patterns and predictive values of semantic memory deterioration among individuals in the earliest stages of AD.