Imaging the human hippocampus with optically-pumped magnetoencephalography

Daniel N Barry,Tim M Tierney,Niall Holmes,Elena Boto,Gillian Roberts,James Leggett,Richard Bowtell,Matthew J Brookes,Gareth R Barnes,Eleanor A Maguire

doi:10.1016/j.neuroimage.2019.116192

Daniel N Barry, Tim M Tierney + Show 8 more

Open Access

https://doi.org/10.1016/j.neuroimage.2019.116192

Copy DOI

Abstract

Optically-pumped (OP) magnetometers allow magnetoencephalography (MEG) to be performed while a participant’s head is unconstrained. To fully leverage this new technology, and in particular its capacity for mobility, the activity of deep brain structures which facilitate explorative behaviours such as navigation, must be detectable using OP-MEG. One such crucial brain region is the hippocampus. Here we had three healthy adult participants perform a hippocampal-dependent task – the imagination of novel scene imagery – while being scanned using OP-MEG. A conjunction analysis across these three participants revealed a significant change in theta power in the medial temporal lobe. The peak of this activated cluster was located in the anterior hippocampus. We repeated the experiment with the same participants in a conventional SQUID-MEG scanner and found similar engagement of the medial temporal lobe, also with a peak in the anterior hippocampus. These OP-MEG findings indicate exciting new opportunities for investigating the neural correlates of a range of crucial cognitive functions in naturalistic contexts including spatial navigation, episodic memory and social interactions.

Highlights

The development of optically-pumped (OP) magnetometers represents a significant evolution of magnetoencephalography (MEG) technology (Boto et al, 2018)
A conjunction analysis across the three participants revealed a cluster of significant voxels (q < 0.005) in the medial temporal lobe with a peak in the right anterior hippocampus (x 1⁄4 36, y 1⁄4 À8, z 1⁄4 À16, F statistic 1⁄4 25.19)
Even when participants’ movements were unconstrained, task-related modulation of theta power in the medial temporal lobe was observable, with a peak in the anterior hippocampus

Summary

Introduction

The development of optically-pumped (OP) magnetometers represents a significant evolution of magnetoencephalography (MEG) technology (Boto et al, 2018). As OP-MEG does not require cryogenic cooling, the sensors can be placed directly on the scalp, and the resulting proximity to the brain increases the magnitude of the measured OP-MEG signal (Boto et al, 2017; Iivanainen et al, 2017) Another significant advance associated with OP-MEG is the capacity for participant movement. To fully leverage the wearability of OPMEG in such a real-world domain, one must be able to detect signal from brain structures upon which behaviours like navigation depend, such as the hippocampus (Maguire et al, 2006) This brain region is located deep in the medial temporal lobe, and the distance from MEG sensors affects the sensitivity with which hippocampal activity can be detected (Hillebrand and Barnes, 2002). To date, there exists no empirical evidence that hippocampal activity can be successfully imaged during the performance of a cognitive task using OP-MEG

Methods

Results

Conclusion