Characterization of the hemodynamic response of the hippocampal and parahippocampal regions using FMRI

Previous neuroimaging studies have suggested a dominant role of the right medial temporal lobe (MTL) structures- the hippocampal and parahippocampal regions in spatial memory processing. However, the underlying physiological hemodynamic response functions (HRF) of the MTL substructures remain undefined. Given the neuroanatomical differences between these substructures, it is posited that their hemodynamic characteristics are distinct. In this study, the hemodynamic responses of the MTL substructures are investigated using an optimization algorithm that penalizes the curvature (i.e. second derivative) of HRF. The time-to-peak characteristic of the hemodynamic responses revealed that the right CA3 and DG subfields of the hippocampus are significantly more active than the right CA1 subfield during a specific spatial memory task. Further, the hemodynamic responses of the entorhinal, perirhinal and parahippocampal cortices are presented. Together, these findings may help advance our understanding of neurodegenerative diseases like epilepsy and Alzheimer’s disease that are strongly associated to hippocampal dysfunction.