Characterizing BOLD activation patterns in the human hippocampus with laminar fMRI

Area of Science:

• Neuroscience
• Human Brain Imaging
• Mesoscale Neuroscience

Background:

• Macroscale functional magnetic resonance imaging (fMRI) extensively studies the human hippocampus.
• Mesoscale (laminar) investigations of human hippocampal microcircuits remain largely unaddressed.
• Understanding laminar responses is crucial for interpreting fMRI data.

Purpose of the Study:

• To investigate venous bias effects on hippocampal laminar fMRI interpretation.
• To establish a benchmark laminar fMRI experiment for robust hippocampal activation using GRE-BOLD contrast.
• To characterize GRE-BOLD responses, T2*, tSNR, and physiological noise across cortical depth in human hippocampal subfields.

Main Methods:

• Comprehensive characterization of GRE-BOLD responses, T2*, tSNR, and physiological noise as a function of cortical depth.
• Utilizing an autobiographical memory paradigm.
• Acquiring depth-specific BOLD responses in individual hippocampal subfields.

Main Results:

• Vascular architecture differences between hippocampal subfields result in subfield-specific laminar GRE-BOLD response biases.
• Robust, depth-specific BOLD responses were successfully acquired in hippocampal subfields during an autobiographical memory task.
• CA1 and subiculum subregions showed more pronounced trisynaptic pathway input than direct entorhinal cortex input during memory retrieval.

Conclusions:

• The study provides novel mesoscale insights into the human hippocampus.
• Findings will aid in interpreting hippocampal laminar fMRI responses.
• The established methodology allows for testing mechanistic hypotheses of hippocampal function.