Patterns of hippocampal-cortical interaction dissociate temporal lobe memory subsystems

A distributed network of brain regions supports memory retrieval in humans, but little is known about the functional interactions between areas within this system. During functional magnetic resonance imaging (fMRI), subjects retrieved real-world memories: autobiographical events, public events, aut obiographical facts, and general knowledge. A common memory retrieval netwo rk was found to support all memory types. However, examination of the corre lations (i.e., effective connectivity) between the activity of brain region s within the temporal lobe revealed significant changes dependent on the ty pe of memory being retrieved. Medially, effective connectivity between the parahippocampal cortex and hippocampus increased for recollection of autobi ographical events relative to other memory types. Laterally, effective conn ectivity between the middle temporal gyrus and temporal pole increased duri ng retrieval of general knowledge and public events. The memory types that dissociate the common system into its subsystems correspond to those that t ypically distinguish between patients at initial phases of Alzheimer's dise ase or semantic dementia. This approach, therefore, opens the door to new l ines of research into memory degeneration, capitalizing on the functional i ntegration of different memory-involved regions. Indeed, the ability to exa mine interregional interactions may have important diagnostic and prognosti c implications. (C) 2000 Wiley-Liss, Inc.