Elsevier

Biological Psychology

Volume 85, Issue 2, October 2010, Pages 350-354
Biological Psychology

Brief report
Disorder specificity despite comorbidity: Resting EEG alpha asymmetry in major depressive disorder and post-traumatic stress disorder

https://doi.org/10.1016/j.biopsycho.2010.08.001Get rights and content

Abstract

The approach-withdrawal and valence-arousal models highlight that specific brain laterality profiles may distinguish depression and anxiety. However, studies remain to be conducted in multiple clinical populations that directly test the diagnostic specificity of these hypotheses. The current study compared electroencephalographic data under resting state, eyes closed conditions in patients with major depressive disorder (MDD) (N = 15) and post-traumatic stress disorder (PTSD) (N = 14) relative to healthy controls (N = 15) to examine the specificity of brain laterality in these disorders. Key findings included (1) reduced left-frontal activity in MDD, (2) a positive correlation between PTSD severity and right-frontal lateralisation, (3) greater activity in PTSD patients relative to MDD within the right-parietotemporal region, and (4) globally increased alpha power in MDD. Findings partially support the diagnostic applicability of the theoretical frameworks. Future studies may benefit from examining task-driven differences between groups.

Introduction

Affective style is fundamental to our adaptive functioning as social beings and may be a key vulnerability factor governing risk for depression and anxiety. Theoretical neuropsychological frameworks relating to affective style include the approach-withdrawal (Davidson, 1998) and the valence-arousal (Heller and Nitschke, 2006, Heller, 1993) models. Depression is associated with an under-activation of the approach system and/or over-activation of the withdrawal system, while anxiety disorders characterised by hyperarousal (e.g. post-traumatic stress disorder) are associated with an over-activation of the withdrawal system (see Kemp and Felmingham, 2008, Shankman, 2003 for discussion). The valence-arousal model expands on the approach-withdrawal model to incorporate the dimension of arousal, which is hypothesised to relate to right-parietotemporal activity (Heller, 1993). This model indicates that depressed patients will exhibit hypo-activity, while patients with anxiety will exhibit hyper-activity in this region. An updated valence-arousal model indicates that different subtypes of anxiety (e.g. generalised anxiety disorder vs. PTSD) may exhibit different patterns of regional brain activity (Heller and Nitschke, 2006; see also Mathersul et al., 2008). ‘Anxious apprehension’, characterised by verbal rumination and worry, is linked to left-sided anterior activity due to its dominance in language function, while ‘anxious arousal’, characterised by physiological arousal and hyper-reactivity, is linked to increased right-hemispheric activity (including frontal and posterior regions). However, studies remain to be conducted that directly contrast depression and anxiety disorders with hyperarousal, such as PTSD.

We have previously reported that anxious arousal is associated with greater right-frontal resting EEG activity, while anxious apprehension is associated with greater left-frontal EEG activity (Mathersul et al., 2008). While these findings support the updated valence-arousal model, we were unable to support hypotheses for the right-parietotemporal region, suggesting that hypothesised differences in right-parietotemporal activity (arousal) may require clinical samples (but see Keller et al., 2000). Other research has reported that depressed patients with anxiety disorder display greater resting EEG activation over right than left (anterior and posterior) hemisphere sites, whereas depressed patients without an anxiety disorder showed the opposite asymmetry at parietal sites (Bruder et al., 1997). An EEG study on patients with PTSD reported an association between arousal symptoms and right-sided parietal activation, although the hypothesised right-sided frontal asymmetry was not observed (Metzger et al., 2004). Recently, a magnetoencephalographic study reported hypofunction of the right-parietotemporal region in patients with major depressive disorder during presentation of highly arousing emotional pictures relative to controls (Moratti et al., 2008). However, contradictory findings have also been reported (e.g. Rabe et al., 2006, Reid et al., 1998) and studies remain to be conducted that directly compare the mood and anxiety disorders.

Here we compare patients with major depressive disorder (MDD), a disorder characterised by reduced approach and hypoarousal, and PTSD, an exemplar of increased withdrawal and hyperarousal, providing an opportunity for testing explicit hypotheses relating to the valence-arousal model. The following directional hypotheses were proposed. Hypothesis 1: Individuals with MDD and PTSD will exhibit greater right-lateralised frontal activity during resting state than healthy controls. Hypothesis 2: Patients with PTSD will exhibit higher right-parietotemporal activity than patients with MDD during resting state, while controls will exhibit activation in between PTSD and MDD.

Section snippets

Participants

Fourteen patients with post-traumatic stress disorder (PTSD, 5 males, 9 females, age mean = 41.4 years, SD = 12.3, 14 right-handed)2, 15 patients with major depressive disorder (MDD, 6 males, 9 females, age mean = 39.9 years, SD = 14.0, 14 right-handed), and 15 healthy controls (6 males, 9 females, age mean = 42.4, SD = 16.7, 14 right-handed)3 were selected from the Brain Resource International

Participant characteristics

No significant differences were observed between groups on handedness data (F(2,41) = 0.458, p = 0.636). Groups differed on depression scores, F(2,41) = 252.55, p < 0.001, such that MDD displayed higher scores than PTSD, p < 0.001, and controls, p < 0.001. PTSD also had higher scores than controls, p < 0.001. Groups also differed on anxiety scores, F(2,41) = 14.80, p < 0.001, such that PTSD and MDD displayed higher scores than controls, p < 0.001. However, the PTSD group did not differ from MDD on anxiety. Groups

Discussion and conclusions

This study compared the resting EEG laterality of frontal and parietotemporal regions in MDD, PTSD, and healthy controls, hence directly testing the hypotheses of the approach-withdrawal and valence-arousal models. Key findings include: (i) reduced left-sided asymmetry in MDD participants relative to controls; (ii) a positive correlation between PTSD severity and right-frontal lateralisation; (iii) discrimination of clinical groupings within the right-parietotemporal region. While these models

Acknowledgements

This research was supported by a NHMRC Program Grant (300304), NHMRC Project Grants (464863 & 464820) and an ARC Discovery Project (DP0987332). AHK is supported by a National Health and Medical Research Council (NHMRC) Career Development Award (571101). We acknowledge the data and support provided by BRAINnet; www.BRAINnet.net, under the governance of the BRAINnet Foundation. BRAINnet is the scientific network that coordinates access to the Brain Resource International Database for independent

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