Functional imaging of hippocampal layers using VASO and BOLD on the Next Generation (NexGen) 7T Scanner

Spatial accuracy and venous biases are a central concern in mesoscale fMRI, with subcortical brain regions facing additional challenges due to lower sensitivity, high physiological noise, and complicated vasculature. Here, we optimized CBV VASO on the NexGen 7T scanner for layer-specific investigations of the hippocampus. The presence of venous biases in VASO and BOLD (from the same acquisition) was then compared by using an established autobiographical memory task. While the activation patterns converged at macroscale, layer-specific differences emerged in the hippocampal subiculum, consistent with venous bias in the inner layers of the subiculum which can be explained by the unique two-sided venous drainage. Further, both VASO and BOLD supported an anterior-posterior dissociation between retrieval stages and functional connectivity with neocortical networks. Thus, hippocampal fMRI allows mapping layer function with high accuracy, and can provide deeper insights into a number of neuropsychological phenomena and the early changes occurring in Alzheimer’s disease.