The effect of age on relational encoding as revealed by hippocampal functional connectivity.

The neural processes mediating cognition occur in networks distributed throughout the brain. The encoding and retrieval of relational memories, memories for multiple items or multifeatural events, is supported by a network of brain regions, particularly the hippocampus. The hippocampal coupling hypothesis suggests that the hippocampus is functionally connected with the default mode network (DMN) during retrieval, but during encoding, decouples from the DMN. Based on prior research suggesting that older adults are less able to modulate between brain network states, we tested the hypothesis that older adults' hippocampus would show functional connectivity with the DMN during relational encoding. The results suggest that, while the hippocampus is functionally connected to some regions of the DMN during relational encoding in both younger and older adults, older adults show additional DMN connectivity. Such age-related changes in network modulation appear not to be mediated by compensatory processes, but rather to reflect a form of neural inefficiency, most likely due to reduced inhibition.