Adult lifespan effects on functional specialization along the hippocampal long axis

There has been increasing attention to differences in function along the hippocampal long axis, with the posterior hippocampus proposed to be well suited to representing fine-grained details and the anterior hippocampus having coarser representations. Whether long axis functional specialization persists into older age is not well understood, despite known age-related declines in the level of detail in memories. In this study, we used a large database of resting state fMRI data (n =322 humans of both sexes included) from across the adult lifespan (ages 18-88) to determine the degree of functional differentiation across the hippocampal posterior-anterior axis. Our first approach was to measure the similarity among signals within hippocampal subregions. We found that signals within the most posterior hippocampal subregion became more similar to one another in older age, but this effect did not relate to memory performance. As a second approach, we measured functional connectivity between hippocampal subregions and the rest of the brain. The functional connectivity profiles of the posterior and anterior hippocampal subregions became more distinct from one another with increasing age, driven by relative stability in anterior hippocampal functional connectivity but more significant age-related differences in posterior subregions of the hippocampus. Stronger connectivity between the anterior hippocampus and several cortical regions was associated with better memory performance in older adults, suggesting that maintenance of anterior hippocampal connectivity may help preserve episodic memory among high performing older adults.