Thalamus & Related Systems 2 (2003) 231–238 Thalamic theta field potentials and EEG: high thalamocortical coherence in patients with neurogenic pain, epilepsy and movement disorders J. Sarnthein ∗ , A. Morel, A. von Stein 1 , D. Jeanmonod Funktionelle Neurochirurgie, Universitätsspital, CH-8091 Zürich, Switzerland Accepted 30 April 2003 Abstract We simultaneously recorded local field potentials (LFP) in the thalamus and EEG on the scalp of 17 patients suffering from neurogenic pain, epilepsy and movement disorders. The EEG of 11 patients displayed enhanced power in the theta frequency range (4–8 Hz). The thalamic LFP of 14 patients peaked in the theta range. The theta coherence between EEG and LFP was significant for 12 patients and reached strengths up to 70%. These findings suggest that enhanced theta rhythmicity occurs in tight functional thalamocortical loops and is a major element in all three diseases investigated. To investigate second-order phase-coupling between LFP frequency components, we computed the bicoherence and averaged over the group of patients. We found peaks in the theta band and the beta band (14–30 Hz), indicating phase correlations of oscillatory events in these frequency ranges with their first harmonic. A further peak indicates that phase coupling occurred also between theta and beta frequencies. This indicates a strong functional interaction between the generators of these oscillations. We also computed the cross-correlation between LFP spectral power at different frequencies. Although this measure is independent of phase, we found good agreement with the bicoherence patterns, pointing again to strong interaction between theta and beta rhythmicity. The overproduction of theta rhythms, the thalamocortical coherence and the correlation of theta with beta rhythms are key elements for the understanding of thalamocortical dysrhythmia (TCD). © 2003 Elsevier Ltd. All rights reserved. Keywords: Bicoherence; LFP; Power correlation; Thalamocortical dysrhythmia 1. Introduction Thalamic and cortical areas are densely and reciprocally interconnected (Steriade et al., 1997; Jones, 2001) and exten- sive studies by in vivo techniques, in anaesthetized prepara- tions and in awake animals have investigated the functional roles of the thalamocortical system (Llinás and Jahnsen, 1982; Steriade, 2001). At the thalamic cellular level, ionic channel properties are at the base of the appearance of spe- cific discharge patterns. As an example, low-threshold cal- cium spike (LTS) bursts have been described intracellularly in in vitro and in vivo experiments and related to a state of membrane hyperpolarization (Llinás and Jahnsen, 1982; Steriade, 2001). At the network level, temporal and spatial patterns of activity in cortical and thalamic areas demon- strate wide variability, suggesting that the reverberating thalamocortical circuit supports a wide range of dynamic interactions necessary for input analysis, motor program- ∗ Corresponding author. Tel.: +41-1-255-2179; fax: +41-1-255-8946. E-mail address: johannes.sarnthein@usz.ch (J. Sarnthein). 1 Deceased on 31 May 2002. ming and cognitive functions (Llinás and Ribary, 1993; McCormick and Contreras, 2001; Steriade, 2001). Based on the above physiological evidence as well as on human thalamic unit recordings (Jeanmonod et al., 1996) and MEG measurements (Llinás et al., 1999), we proposed that a single global mechanism involving the thalamocortical reentry loop is responsible for the generation of the five do- mains of positive symptoms that clinically characterize the so-called thalamocortical dysrhythmia (TCD) (Llinás et al., 1999; Jeanmonod et al., 2001; Llinás et al., 2001). These domains include neurogenic pain, epilepsy, tinnitus, move- ment and neuropsychiatric disorders. The present study focuses on the interaction between tha- lamus and cortex. In the course of surgical interventions we simultaneously measured EEG on the scalp and local field potentials (LFP) in the thalamus of patients suffering from neurogenic pain, epilepsy and movement disorders. Our main findings are: (1) high power in the theta frequency range (4–8 Hz) of the LFP in thalamic areas where LTS have been reported (Jeanmonod et al., 1996; Magnin et al., 2000), (2) high coherence between EEG and LFP most markedly in the theta band, and (3) a strong interaction between LFP 1472-9288/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1472-9288(03)00021-9