Persistent EEG overactivation in the cortical pain matrix of neurogenic pain patients

Functional brain imaging of pain over the last years has provided insight into a distributed anatomical matrix involved in pain processing which includes multiple cortical areas. EEG/MEG-based imaging studies have mostly relied on settings of evoked nociception. We report here the spontaneous presence of enhanced activations in the pain matrix of the patient group on the basis of continuous EEG and functional Low Resolution Electromagnetic Tomography (LORETA) from 16 chronic neurogenic pain patients and 16 healthy controls. These overactivations occurred predominantly within the high theta (6-9 Hz) and low beta frequency ranges (12-16 Hz). Theta and beta overactivations were localized to multiple pain-associated areas, primarily to insular (IC), anterior cingulate (ACC), prefrontal, and inferior posterior parietal cortices, as well as to primary (S1), secondary (S2), and supplementary somatosensory (SSA) cortices. After a therapeutic lesion in the thalamus (central lateral thalamotomy, CLT), we followed a subgroup of 6 patients. Twelve months after surgery, activation in cingulate and insular cortices was significantly reduced. The presence of rhythmic processes in multiple, partially overlapping areas of the cortical pain matrix concur with the concept of thalamocortical dysrhythmia (TCD) that predicts increased thalamocortical low and high frequency oscillations ensuing from thalamic desactivation. These spontaneous, ongoing, frequency-specific overactivations may therefore serve as an anatomo-physiological hallmark of the processes underlying chronic neurogenic pain.