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The electrophysiology of human memory - Michael Kahana

Michael Kahana
October 8, 2020 - 9:55am to 10:40am
Zoom

Michael Kahana, PhD

Professor of Psychology
University of Pennsylvania

 

Abstract

Human memory function is highly variable, fluctuating between periods of high and low performance even within a given person. Neurosurgical patients with indwelling electrodes present a unique opportunity to study the neural correlates of this variability and to define both the features of neural activity at a given brain location and the functional connections between brain regions that predict variability in memory encoding and retrieval. Here, I will describe our recent efforts to characterize brain networks that support memory via correlative (passive neural recording) and causal (direct electrical stimulation) approaches. Throughout the brain, we find that low-frequency networks exhibit reduced local power but stronger functional connectivity during successful episodic encoding and retrieval. Furthermore, many canonical memory regions emerge as hubs of such low-frequency connections, including the lateral frontotemporal cortices, the parahippocampal gyrus – and within it – the entorhinal cortex. High-frequency bands (i.e. gamma, 30+ Hz) almost exclusively exhibit desynchronization during successful memory operations. We recently extended these correlative studies and used intracranial stimulation to ask whether functional connections imply causality. We confirmed that electrical stimulation evokes increases in theta power at remote regions, as predicted by the strength of low-frequency functional connections. This relation was strongest when stimulation occurred in or near white matter. These findings demonstrate the importance of low-frequency connectivity to episodic memory, integrating these findings over spatial scales and through causal and correlative approaches.

Bio

Michael Jacob Kahana, Ph.D., is the Edmund J. and Louise W. Kahn Term Professor of Psychology at the University of Pennsylvania. Kahana’s work combines behavioral, neural, and computational approaches to the study of human memory. Kahana obtained his doctoral training at the University of Toronto (1990-1993), where he studied under the mentorship of Bennet B. Murdock and Endel Tulving. Kahana then obtained postdoctoral training at Harvard University (1993-1994) under the mentorship of William K. Estes. He then became an assistant professor at Brandeis University in 1994, and an associate professor in 2000. He joined the University of Pennsylvania as Professor in 2004. 
Kahana began his training at Toronto in experimental psychology, with a particular focus on mathematical models of human memory. Inspired by Murdock’s distributed memory modeling and Tulving’s theorizing about episodic memory, Kahana sought to develop a computational framework that could explain Tulving’s conception of mental time travel using a distributed, associative memory model. While an assistant professor at Brandeis, Kahana and his then graduate student, Marc Howard, developed a retrieved-context theory of episodic memory, which he and his students have continued to develop and extend over the years. Kahana also became inspired by both his students and colleagues to investigate the neural mechanisms of human memory, an activity that has characterized much of his work over the last 20 years. Work conducted in his lab by former trainees, Jeremy Caplan, Arne Ekstrom, and Josh Jacobs, identified and characterized theta oscillations, place cells, and grid cells in the human brain. In subsequent work, Kahana and his trainees have focused on using high frequency neural activity to characterize the spatio-temporal dynamics of memory encoding and retrieval. Most recently, Kahana’s lab has begun to use direct brain stimulation as a manipulative tool for elucidating the physiological mechanisms underlying episodic memory and for investigating the potential use of closed-loop brain stimulation to improve memory in patients with neurological disorders.
Kahana was the 2010 recipient of the Troland Research Award from the U.S. National Academy of Sciences and the 2018 recipient of the Howard Crosby Warren Medal from the Society of Experimental Psychologists and the 2018 recipient of the Mid-Career award from the Psychonomic Society. In 2012, he published Foundations of Human Memory, a monograph that focuses on the interplay between theory and data in the laboratory study of human memory (Oxford University Press).