Episodic memory on the path to Alzheimer's disease

This review is focused on specific circuits of the medial temporal lobe that have become better understood in recent years for their computational properties contributing to episodic memory and to memory impairment associated with aging and other risk for AD. The layer II neurons in the entorhinal cortex and their targets in the dentate gyrus and CA3 region of hippocampus comprise a system that rapidly encodes representations that are distinct from prior memories. Frank neuron loss in the entorhinal cortex is specific for AD, and related structural and functional changes across the network comprised of the entorhinal cortex and the dentate/CA3 regions hold promise for predicting progression on the path to AD.

► Diagnosis and intervention at earliest boundary of AD will be most effective.
► Specific MTL circuits contribute to memory impairment in aging and AD.
► Neuron loss in the entorhinal cortex is specific for AD but not aging.
► Improved structural and functional measures of MTL circuitry to track path to AD.