High thalamocortical theta coherence in patients with neurogenic pain

Patients with severe and chronic neurogenic pain are known to exhibit excess EEG oscillations in the 4- to 9-Hz theta frequency band in comparison with healthy controls. The generators of these excess EEG oscillations are localized in the cortical pain matrix. Since cortex and thalamus are tightly interconnected anatomically, we asked how thalamic activity and EEG are functionally related in these patients. During the surgical intervention in ten patients with neurogenic pain, local field potentials were recorded from the posterior part of the central lateral nucleus (CL). The highest thalamocortical coherence was found in the 4- to 9-Hz theta frequency band (median 7.7 Hz). The magnitude of thalamocortical theta coherence was comparable to the magnitude of EEG coherence between scalp electrode pairs. Median thalamocortical theta coherence was 27%, reached up to 68% and was maximal with frontal midline scalp sites. The observed high thalamocortical coherence underlines the importance of the thalamus for the synchronization of scalp EEG. We discuss the pathophysiology within the framework of a dysrhythmic thalamocortical interplay, which has important consequences for the choice of therapeutic strategy in patients with chronic and severe forms of neurogenic pain.