Mapping hippocampal-cerebellar functional connectivity across the adult lifespan

Although the hippocampus and cerebellum are traditionally considered to support distinct memory systems, evidence from nonhuman species indicates a close bidirectional relationship during learning and navigational behaviour, with the hippocampus projecting to - and receiving input from - several cerebellar regions. However, little is known about the nature and topography of hippocampal-cerebellar connectivity in the human brain. To address this gap, we applied seed-based functional connectivity analyses to resting-state fMRI data from 479 cognitively normal participants, aged 18-88 years. We identified significant functional correlations between the hippocampus and widespread areas of cerebellar cortex, particularly lobules HIV, HV, HVI, HVIIA (Crus I and II), HIX, and HX. Contrasting the left and right hippocampus, we found significant correlations with the contralateral Crus II. We also compared longitudinal subdivisions of the hippocampus, revealing that anterior hippocampus demonstrated stronger connectivity with right Crus II, whereas posterior hippocampus was strongly connected to vermal parts of lobule V. Finally, we found that functional correlations between several hippocampal seeds (left, right, and anterior) and lobules HVI and HV decreased significantly with age. These results provide novel insights into hippocampal-cerebellar functional organisation and the influence of ageing on this system. Further studies are required to establish the role of this connection in learning and memory, as well as its potential vulnerability to neurodegeneration.