Application of cortical unfolding techniques to functional MRI of the human hippocampal region

We describe a new application of cortical unfolding to high-resolution functional magnetic resonance imaging (fMRI) of the human hippocampal region. This procedure includes techniques to segment and unfold the hippocampus, allowing the fusiform, parahippocampal, perirhinal, entorhinal, subicular, and CA fields to be viewed and compared across subjects. Transformation parameters derived from unfolding high-resolution structural images are applied to coplanar, functional images, yielding two-dimensional "unfolded" activation maps of hippocampi. The application of these unfolding techniques greatly enhances the ability of fMRI to localize and characterize signal changes within the medial temporal lobe. Use of this method on a novelty-encoding paradigm reveals a temporal dissociation between activation along the collateral sulcus and activation in the hippocampus proper.