Original Research Article
Independent delta/theta rhythms in the human hippocampus and entorhinal cortex
Florian Mormann 1, 2*, Hannes Osterhage 1, 3, Ralph G. Andrzejak 4, Bernd Weber 1, Guillen Fernandez 5, Juergen Fell 1, Christian E. Elger 1 and Klaus Lehnertz 1, 3
1 Department of Epileptology, University of Bonn, Germany
2 Division of Biology, California Institute of Technology, USA
3 Helmholtz-Institute for Radiation and Nuclear Physics, University of Bonn, Germany
4 Department of Technology, University Pompeu Fabra, Spain
5 F.C. Donders Center for Cognitive Neuroimaging and Dept. of Neurology, Radboud University Nijmegen, The Netherlands
2 Division of Biology, California Institute of Technology, USA
3 Helmholtz-Institute for Radiation and Nuclear Physics, University of Bonn, Germany
4 Department of Technology, University Pompeu Fabra, Spain
5 F.C. Donders Center for Cognitive Neuroimaging and Dept. of Neurology, Radboud University Nijmegen, The Netherlands
Theta oscillations in the medial temporal lobe (MTL) of mammals are involved in various functions such as spatial navigation, sensorimotor integration, and cognitive processing. While the theta rhythm was originally assumed to originate in the medial septum, more recent studies suggest autonomous theta generation in the MTL. Although coherence between entorhinal and hippocampal theta activity has been found to influence memory formation, it remains unclear whether these two structures can generate theta independently. In this study we analyzed intracranial electroencephalographic (EEG) recordings from 22 patients with unilateral hippocampal sclerosis undergoing presurgical evaluation prior to resection of the epileptic focus. Using a wavelet-based, frequency-band-specific measure of phase synchronization, we quantified synchrony between 10 different recording sites along the longitudinal axis of the hippocampal formation in the non-epileptic brain hemisphere. We compared EEG synchrony between adjacent recording sites (i) within the entorhinal cortex, (ii) within the hippocampus, and (iii) between the hippocampus and entorhinal cortex. We observed a significant interregional gap in synchrony for the delta and theta band, indicating the existence of independent delta/theta rhythms in different subregions of the human MTL. The interaction of these rhythms could represent the temporal basis for the information processing required for mnemonic encoding and retrieval.
Keywords: medial temporal lobe, intracranial EEG, oscillations, synchronization, wavelet, phase precession
Copyright: © 2008 Mormann, Osterhage, Andrzejak, Weber, Fernandez, Fell, Elger and Lehnertz. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.
*Correspondence: Florian Mormann, Division of Biology, California Institute of Technology, MS 216-76, 1200 E California Blvd, Pasadena, CA 91125, USA. e-mail: fmormann@yahoo.de
Citation: Mormann F, Osterhage H, Andrzejak RG, Weber B, Fernandez G, Fell J, Elger CE and Lehnertz K (2008) Independent delta/theta rhythms in the human hippocampus and entorhinal cortex. Front. Hum. Neurosci. (2008) 2:3. doi:10.3389/neuro.09.003.2008
Received: 25 January 2008; paper pending published: 08 April 2008; accepted: 06 May 2008; published online: 22 May 2008.
Edited by:
Hans-Jochen Heinze, Otto-von-Guericke-University, Germany; University of Magdeburg, Germany
Reviewed by:
Rodrigo Quian Quiroga, University of Leicester, UK
Christoph S. Herrmann, Otto-von-Guericke-University, Germany
Christoph S. Herrmann, Otto-von-Guericke-University, Germany
*Correspondence: Florian Mormann, Division of Biology, California Institute of Technology, MS 216-76, 1200 E California Blvd, Pasadena, CA 91125, USA. e-mail: fmormann@yahoo.de
