Emotional Modulation of Frontal Alpha Asymmetry - a Novel Biomarker of Mild Traumatic Brain Injury

Abstract

Objective findings of brain injury or dysfunction are typically lacking in mild traumatic brain injury (MTBI) despite prolonged post-concussion symptoms in some patients. Thus, there is a need for objective biomarkers of MTBI that reflect altered brain physiology underlying subjective symptoms. We have previously reported increased attention to threat-related stimuli in subjects with MTBI, suggesting a physiological vulnerability to depression. Vulnerability to depression has been linked with relatively greater activity of the right than left frontal cortex reflected in inverse pattern in frontal alpha with greater power on the left than right. We investigated whether patients with previous MTBI show this pattern of frontal activity reflected in more negative frontal alpha asymmetry (FAA) scores. Furthermore, in search for potential biomarkers of MTBI, we created a novel index, emotional modulation of FAA (eFAA) and investigated whether it correlates with subjective symptoms. EEG was recorded while subjects with previous MTBI and controls performed a computer-based reaction time task integrating different cognitive executive functions and containing either threat-related or emotionally neutral visual stimuli. Post-concussion symptoms and depression were assessed using the Rivermead Post-Concussion Symptoms Questionnaire (RPQ) and Beck’s depression inventory (BDI). Task-induced FAA was assessed and eFAA calculated by subtracting FAA in the context of neutral stimuli from FAA in the context of emotional stimuli. The MTBI group showed FAA scores reflecting relatively greater right-sided frontal activity compared to healthy controls. eFAA differentiated the symptomatic MTBI from non-symptomatic MTBI group and from healthy controls. eFAA also correlated with RPQ and BDI scores. In conclusion, FAA pattern previously linked with vulnerability to depression, was observed in patients with previous MTBI. Furthermore, eFAA has potential as a biomarker of altered affective brain functions in MTBI.

Emotion-Attention Interaction in the Right Hemisphere

“…This scheme provides a setting where subtle alterations in emotion-attention interaction and emotional control are likely reflected in FAA, unlike during resting state FAA measurements. During active engagement of the frontal circuits, we have shown that emotional modulation of FAA (eFAA) correlates with emotionally modulated behaviors [142] and depressive symptoms [143]. This novel biomarker, eFAA, could overcome some of the weaknesses of the resting state FAA and be a more reliable biomarker of alteration in emotion-attention interaction, extending beyond depression [142,143].…”

“…Consequently, it has potential as a biomarker for affective brain functions. Such biomarkers have shown potential applicability for assessing the impact of neuromodulation [142] and the impact of MTBI on affective neural circuits and functions [143].…”

“…As resting state FAA has so far failed to be a reliable clinical biomarker of depression [147], we have developed a novel biomarker, based on task-induced FAA, in threatening contexts [142,143]. Engaging frontal networks with a task involving executive functions and right hemispheric networks with negative emotional stimuli allows the assessment of FAA, when competition between an executive function task and emotion-related processes occurs and emotional control is required.…”

“…The applicability of brain physiology-based measures, such as eFAA, reflecting the engagement of the right hemisphere in affective and attentional processes is not limited to the clinical and neuroscientific fields but extends to the field of technology. Biomarkers that are based on measuring especially the right hemisphere's engagement in a task with emotional content, such as emotional modulation of FAA [143] and threat-modulation of executive function [12], may be used to asses not only clinical populations, such as head injury and depression, but also healthy subjects in interaction with novel technologies. For example, FAA derived measures may be used to study the impact of humanoid robots' emotional behaviors on human user's emotional responses.…”