A review of the literature on the impact of acute and chronic stress upon brain waves

Abstract

Background: The biological responses associated with stress originate in the brain and involve different physiological and physical effects. The direct effect of stress on cortical responses can be visualized by recording the brain’s electrical waves using an encephalograph. These waves are recorded by means of an electroencephalogram (EEG). EEG is the most commonly used neuroimaging technique to study the patterns of brainwaves and functioning of the brain. It also measures the variation of the electric field produced by neuronal activity a millisecond at a time. To systematically analyze published studies on the difference between brain wave patterns in terms of their frequencies among subjects with acute stress, chronic stress, and normal individuals. 
 Methodology: The data from published studies was arranged quantitatively and qualitatively by producing a planned summary measure. Studies that focused on brain wave analysis of the EEG of healthy adult subjects with no history of mental illness or head injury were included in the review. The selected literature included many types of stressors that are acute or chronic, and that affected the neuronal electrical activity. The only electronic database utilized to identify relevant studies was PubMed.
 Result: Fifteen studies were included that were based on a variety of acute stressors to observe alterations in brain wave activity between stress-free and stressed states. These studies showed that stressors could be a causative factor to generate fluctuations in neuronal oscillations that also leads to significant psychological, physiological and neurobiological deteriorations to some extent. An additional sixteen studies were included, which showed the effect of chronic stress on the asymmetry of the amplitude in the frequencies of brain waves. 
 Conclusion: The most common change observed was in the alpha frequency (8-13Hz), followed by changes in beta waves (13-30 Hz) and theta (4-8Hz). Though, there is not always the same resultant pattern of waves explored with even the same type of stressors due to interpersonal differences in response to a stressful situation.