Eye movements reflect memory-related theta activity in the human brain

Area of Science:

• Neuroscience
• Cognitive Science
• Memory Research

Background:

• Theta oscillations in the medial temporal lobe (MTL), including the hippocampus, are crucial for memory across species.
• The relationship between physical movement and theta activity is well-established in rodents but less clear in primates, possibly due to reliance on visual search for navigation.

Purpose of the Study:

• To investigate the relationship between theta oscillations in the human MTL and eye movements during ambulatory navigation.
• To determine if visual search strategies influence MTL theta activity, particularly under memory demands.

Main Methods:

• Analysis of intracranial electroencephalographic (iEEG) data from the human MTL.
• Simultaneous recording of iEEG activity with body and eye movements during navigation tasks.
• Examination of theta power modulation in relation to saccadic eye movements and memory performance.

Main Results:

• MTL theta power was significantly elevated during saccadic eye movements, specifically when memory demands were present.
• Increased theta power correlated with exploratory gaze patterns, better memory performance, and early route planning phases.
• Theta phase aligned with saccade onset during both memory-guided and visually-guided navigation, indicating temporal structuring of MTL activity by eye movements.

Conclusions:

• Memory-related theta dynamics in the human MTL are closely linked to visual search and planning during navigation.
• Saccadic eye movements may play a role in organizing mnemonic computations within the MTL during naturalistic navigation.
• Findings highlight a mechanism connecting eye movements, spatial memory, and MTL theta oscillations in humans.