A preserved neural code for temporal order between memory formation and recall in the human medial temporal lobe

bioRxiv (Cold Spring Harbor Laboratory)

Abstract

Temporal memory enables us to remember the temporal order of events happening in our life. The human medial temporal lobe (MTL) appears to contain neural representations supporting temporal memory formation, but the cellular mechanisms that preserve temporal order information for recall are largely unknown. Here, we examined whether human MTL neuronal activity represents the temporal position of events during memory formation and recall, using invasive single and multi-unit recordings in human epilepsy patients (n = 19). Participants freely navigated a virtual environment in order to explore and remember locations and temporal positions of objects. During each exploration period, they sequentially encountered two or three different objects, placed in different locations. This allowed us to examine single- and multi-unit neuronal firing rates (FR) as a function of the temporal position the objects were presented in. We found that a significant number of multi-units and single-units in various MTL regions including the hippocampus showed selectivity to the temporal position of objects during the exploration period. During recall, patients were asked to indicate which one of two objects from the same trial was found latter. Neural firing rates during recall showed a selectivity supporting recall of temporal positions. Interestingly, most of the selective single-units that stayed selective during encoding and recall preserved their temporal position preference. Our results thus suggest that neuronal activity in the human MTL contains a preserved neural code for temporal order in memory formation and recall.

Authors 7

1. Mohammad Farhan Khazali corresponding

   University of Freiburg · University Medical Center Freiburg

   Affiliation as printed

   Epilepsy Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany

   University Medical Center Freiburg

2. Armin Brandt

   University of Freiburg · University Medical Center Freiburg

   Affiliation as printed

   Epilepsy Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany

   University Medical Center Freiburg

3. Peter Christoph Reinacher Aachen Fraunhofer Institute for Laser Technology (ILT)

   University of Freiburg · University Medical Center Freiburg · Fraunhofer Institute for Laser Technology

   Affiliation as printed

   Department of Stereotactic and Functional Neurosurgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany

   Fraunhofer Institute for Laser Technology, Aachen, Germany

   University Medical Center Freiburg

4. Michael J. Kahana

   University of Pennsylvania

   Affiliation as printed

   Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA

   University of Pennsylvania

5. Joshua Jacobs

   Columbia University

   Affiliation as printed

   Department of Biomedical Engineering, Columbia University, New York, NY, USA

   Columbia University

6. Andreas Schulze‐Bonhage

   University of Freiburg · University Medical Center Freiburg

   Affiliation as printed

   Epilepsy Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany

   University Medical Center Freiburg

7. Lukas Kunz

   University Hospital Bonn

   Affiliation as printed

   Department of Epileptology, University Hospital Bonn, Bonn, Germany

   University Hospital Bonn