A European-American research team has used electrophysiological data to prove the presence of grid-like activity in the human brain. Researchers used various methods to visualize grid cell activity while subjects explored images of everyday scenes under the direction of Prof. Christian Doeller of the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig and Dr. Tobias Staudigl of the Donders Institute for Brain, Cognition, and Behavior, Radboud University, The Netherlands.
The “place cells” of the human hippocampus are in charge of coding one’s spatial position. Grid cells, a similar type of brain cell, are one of the basic building blocks of spatial navigation, storing a range of places that are uniformly dispersed throughout multiple brain areas. This results in a honeycomb pattern tiling, which was observed in the entorhinal cortex.
“We assume that these spatial coding principles in the brain form the basis of higher cognitive performance–here in this study, in the field of perception, but possibly also in decision-making or even in social interaction,” explained Prof. Doeller.
(A) Paradigm: free viewing of 100 indoor and 100 outdoor scenes with simultaneous eye tracking (left). MEG data are aligned to saccade onsets, defining events of interest (right).
(B) Region of interest (highlighted), comprising bilateral anterior portions of the hippocampus and parahippocampal gyrus. (C) Analysis rationale. Data were split into halves (set 1 and set 2) to estimate the putative grid orientation (angle of hexadirectional activity) separately from computing aligned and misaligned BHA power, in a two-fold cross-validation design. Estimation of putative grid orientation was done by fitting regressors for sine and cosine of saccade directions (Θ) in the respective rotational symmetric space (here: 60° periodicity) to set 1 BHA power (the general linear model included a constant and saccade duration as nuisance regressors). Resulting beta estimates were used to derive the putative grid orientation angle (Φ). Trials in set 2 were split according saccade directions aligned versus misaligned to Φ. The difference in BHA power (aligned − misaligned) reflects the grid-like modulation of BHA power.
Dots show data from all participants; error bars show SEM.
The scientists used two distinct ways to make independent measurements to illustrate the dynamics of brain activity. During a MEG scan, patients sit beneath a type of helmet that detects magnetic fields generated by active nerve cell electrical currents. This allowed for the recording of data that is an expression of the brain’s instantaneous overall activity with no delay. The participants looked at 200 images that included both indoor and outdoor situations.
In addition to the MEG measurements, they also recorded their eye movements using an eye-tracker to determine how they visually explored the scenes of the images shown.
The resulting grid-like modulation of the electromagnetic and intracranial electrophysiological activity is related to the exploration of visual space. The impulses from these cells may generate maps of “cognitive spaces” in which people cognitively arrange and retain the complexity of their internal and external environments.
“We looked at whether the activity patterns of the entire grid cell system have a specific structure.” reports Prof. Doeller. “By showing the subjects pictures of visual scenes, we were able to demonstrate that.”
The study results support the view that grid-like coding goes beyond mapping the environment during locomotion and that the grid cell system could provide a general neural code underlying core cognitive functions in humans.
Hexadirectional Modulation of High-Frequency Electrophysiological Activity in the Human Anterior Medial Temporal Lobe Maps Visual Space, Tobias Staudigl, Marcin Leszczynski, Joshua Jacobs, Charles E. Schroeder, Ole Jensen, Christian F. Doeller.
Published: October 2018
DOI: https://doi.org/10.1016/j.cub.2018.09.035