Age-related changes in the mesial temporal lobe: the parahippocampal white matter region.

The perforant pathway originates from cells in the entorhinal cortex and relays sensory information from the neocortex to the hippocampus, a region critical for memory function. Imaging studies have demonstrated structural alterations in the parahippocampal white matter in the region of the perforant pathway in people at risk for developing Alzheimer's disease. It is not clear, however, if changes noted in this region are indicative of pathological aging or are a function of the normal aging process. We compared magnetic resonance imaging (MRI)-derived mesial temporal lobe volumes in 51 healthy older individuals and 40 young participants, with an emphasis on the parahippocampal white matter. Yearly clinical evaluations showed that 9 of the older cohort declined in cognitive function. Parahippocampal white matter, hippocampal, and entorhinal cortex volumes were significantly reduced in healthy older people who remained stable over time compared with young participants. These findings suggest that volume differences in mesial temporal lobe gray and white matter structures may take place as a result of the normative aging process.