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Cerebral Cortex Advance Access published online on October 27, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp223
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Theta Oscillations Mediate Interaction between Prefrontal Cortex and Medial Temporal Lobe in Human Memory

Kristopher L. Anderson1, Rajasimhan Rajagovindan1, Georges A. Ghacibeh2, Kimford J. Meador3 and Mingzhou Ding1

1 The J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA, 2 Northeast Regional Epilepsy Group, Comprehensive Epilepsy Center, 20 Prospect Avenue, Suite 800, Hackensack, NJ 07601, USA, 3 Department of Neurology, Emory University, Atlanta, GA 30322, USA

Address correspondence to Mingzhou Ding. Email: mding{at}bme.ufl.edu.

The medial temporal lobe (MTL) and the prefrontal cortex (PFC) are known to be critical structures for human memory processes. Furthermore, it has been suggested that they are part of a memory network. Although memory-modulated interaction between PFC and MTL has been observed at the hemodynamic level, it remains unclear what the neuronal process is that mediates the communication between these 2 areas. Experiments in rodents suggest that field oscillations in the theta band (4–8 Hz) facilitate PFC–MTL interaction. No such evidence has been reported in humans. To address this problem, cortical electrical activity from MTL, PFC, and lateral temporal lobe was recorded from implanted electrode grids in 3 epilepsy patients performing a verbal free recall task. The data were analyzed using a parametric spectral method to obtain estimates of power, coherence, and Granger causality. A task-modulated increase in coherence values between PFC and MTL was seen during free recall as opposed to a baseline condition. Concurrently, the number of coherent PFC–MTL site pairs was significantly increased during recall. Granger causality analysis further revealed that the increased coherence is a consequence of higher bidirectional information flow between the 2 regions, with a generally greater driving from MTL to PFC, namely, (MTL->PFC) > (PFC->MTL).

Key Words: coherence • electrocorticogram • Granger causality • intracranial EEG • verbal recall


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