Electromagnetic indices of memory-related theta oscillations and of theta-gamma covariance

Duezel, E., Neufang, M., Schott, B., and Mai, H.
Klinik für Neurologie II, Otto-von-Guericke Universität Magdeburg, Germany
E-mail: emrah.duezel@medizin.uni-magdeburg.de

Theta oscillations and covariance of theta and gamma oscillations are important physiological indices of memory processes in the hippocampus. We show, using whole-head magnetoencephalography, that during the recognition of repeated words from episodic memory, theta oscillations over left temporal sensors have higher amplitudes and show a greater degree of phase alignment than correct rejections of new words. Over similar regions, there are also differences in gamma amplitudes between recognized and correctly rejected words. Remarkably, recognized and new words also differ with respect to the degree to which gamma changes are locked to certain phases of theta. In patients with temporal lobe epilepsy who have unilateral hippocampal sclerosis, both theta oscillations and the theta-gamma phase-coupling are affected over temporal sensors.