Cortical power spectral analysis of acute pathophysiological pain.

In the past decade, advances in quantitative EEG methods, such as the analysis of cortical power spectrum, have proven a useful tool for observing changes in brain activity as a function of physiological and behavioral states. The cortical power spectrum (CPS) is a computer-derived analysis of brain electrical activity using mathematical principles of Fast Fourier Transform function. The total energy output of specific cortical areas can be estimated over time, as a function of EEG spectral frequencies. This report describes the study of CPS in pathophysiological pain patients, using acute dental pain as a model. Seven "walk-in" acute pain patients in an emergency dental clinic were recorded during 10 min of pain, before treatment. Approximately one week later, 10 min recordings during nonpain states were obtained as control. Subjective pain scales and other psychological measures were administered to all subjects before and after recording on each visit. Each 10 min stage of continuous CPS recording consisted of 10 spectra per stage, 6 epochs/spectrum, and 10.24 sec/epoch; each spectrum was stored, averaged, transformed, displayed, printed, and plotted by the Pain Microcomputer System. Results show significant cortical power reduction along all frequency bands (0.5-50 Hz) when pain-states are compared to nonpain states. The magnitude of reduction also appears to correspond to subjective pain report. Analysis for rank order may be inversely related to subjective painfulness, indicating that pain and alpha-desynchronization are closely associated. This study demonstrates that the brain activity of clinical pain patients can be measured. The feasibility of developing a pathophysiological objective pain measuring system is discussed.