RESEARCH ARTICLE

Hemispheric Lateralization Moderates the Life Events– Distress Relationship Daniela Herzog1*†, Tereza Killianova1, Sigrid Pauwels2, Filip Germeys2,3 & Yori Gidron1 1

Vrije Universiteit Brussel, Brussels, Belgium Hogeschool-Universiteit Brussel, Brussels, Belgium 3 University of Leuven, Leuven, Belgium 2

Abstract Past studies show that life events (LE) predict mental distress. This research tested whether hemispheric lateralization (HL) moderated the relationship between LE and mental distress. In studies 1 and 2, different instruments for assessing HL were used (questionnaire and neuropsychological test). In both studies, LE or daily hassles were positively correlated with distress (study 1) and with anxiety and depression (study 2), only in people with right but not left HL, controlling for effects of gender. In study 3, experimentally induced stress led to increased perceived stress, again only in participants with right but not left HL. These results show consistently that left HL may protect against adverse effects of LE, hassles or acute stress on well-being. We propose possible mechanisms and future research directions. Copyright © 2014 John Wiley & Sons, Ltd. Received 26 November 2013; Revised 1 March 2014; Accepted 10 March 2014 Keywords hemispheric lateralization; mood; life events; depression; anxiety; hassles *Correspondence Daniela Herzog, Maccabi Health Services, Israel. † E-mail: [email protected] Published online 10 April 2014 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/smi.2577

Introduction Life events (LE), daily hassles and their consequences have been a focus of inquiry in the field of stress and coping for several decades. LE can be defined as a ‘discontinuity in a person’s life space of which he is aware and which requires new behavioral responses’ (Hopson & Adams, 1976, p. 24). LE are relatively rare positive or negative events, with major or minor consequences, and include, e.g. a car crash, loss of a relative, job loss or loss of marriage. In contrast, daily hassles are ‘repeated or chronic strains of everyday life’ (Delongis, Coyne, Dakof, Folkman, & Lazarus, 1982), usually of less major consequences, and include, e.g. being in traffic jams, missing a train and work overload. Research has examined quite extensively the relationship between major or minor LE and subsequent mental distress. Several studies report a positive relationship between LE and the onset of depression (Billings, Cronkite, & Moos, 1983; Kendler et al., 1995). Furthermore, a meta-analysis of 25 studies found that LE were associated with depression in the elderly (Kraaij, Arensman, & Spinhoven, 2002). Similarly, LE were found to be associated with general anxiety disorders (Blazer, Hughes, & George, 1987; Murphy, Moscicki, Vermund, & Muenz, 2000). The impact of LE and hassles on distress can be different. In the Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

meta-analysis of Kraaij et al. (2002), daily hassles were more strongly related to depression than LE. However, past studies suffered from methodological limitations. Many of the past studies were cross sectional, thus not enabling one to discern the direction of relationships between LE and distress. It is highly probable that during the periods of high distress, people may pay attention to and recall more past negative LE. However, LE were also prospectively found to predict greater risk of depression (Kendler et al., 1995). Another important confounder in past research is gender. There are no significant gender differences in distress; however, men and women report different LE, and the ‘depressogenic’ effects of LE differ between the genders (Kendler, Gardner, Neale, & Prescott, 2001). Thus, effects of gender must be considered or statistically controlled for in this research domain. How could the LE–distress relationship be explained? Three mechanisms are proposed. Firstly, emotional dysregulation and rumination, poor emotional understanding and inappropriate emotional expression were found to mediate the relationship between LE and distress (McLaughlin & Hatzenbuehler, 2009). Secondly, coping strategies that are not suitable to certain LE, in accordance with the ‘goodness of fit’ hypothesis (Forsythe & Compas, 1987; Lazarus & Folkman, 1984), may also 47

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explain this relationship. Specifically, using emotionfocused coping in controllable situations and problemfocused coping in uncontrollable situations, rather than the opposite, has been found to be related to worse outcomes (Levine et al., 1987; Weisenberg, Schwarzwald, Waysman, Solomon, & Klingman, 1993; Zakowski, Hall, Klein, & Baum, 2001). Thirdly, severe traumatic events and repeated exposure to daily hassles both could trigger physiological changes in the hypothalamic–pituitary– adrenal axis and affect sympathovagal balance (DeBeck, Petersen, Jones, & Stickland, 2010; Dickerson & Kemeny, 2004; Dolan, Calloway, Fonagy, De Souza, & Wakeling, 1985), which have both been associated with anxiety and depression (Agelink, Boz, Ullrich, & Andrich, 2002; Lopez-Duran, Kovacs, & George, 2009). A few studies have identified moderators in the LE/hassles–distress relationship. These moderators can be external or internal to the person. One study focusing on external moderators found that having social support or positive LE moderated the LE–depression relationship (Cohen & Hoberman, 1983). Having social support or positive LE reduced the LE–depression relationship. Looking at internal moderators or resources, locus of control was found to interact with LE in relation to depression, such that significant LE–depression correlations existed only in people high on external locus of control (Johnson & Sarason, 1978). Another possible internal resource variable that could also be a moderator is hemispheric lateralization (HL), a stable tendency to utilize or activate one hemisphere versus another (e.g. Davidson, 2004). HL is conceptually and empirically related to mental distress, particularly to mood. Studies have shown that right HL is more consistently associated with negative affect, whereas left HL is related mainly to positive affect (Davidson, 2004; Tomarken, Davidson, Wheeler, & Doss, 1992). In a more recent review of studies in this topic, Hofman (2008) suggested that right HL reflects withdrawal emotions, particularly depression and anxiety, whereas left HL reflects more approach emotions, particularly positive affect and anger/hostility. Davidson and colleagues suggested that HL is not a variable with ‘main effects’, rather it is manifested during stress, termed as the ‘stress × diathesis’ model. Indeed, in a series of studies, people with right HL demonstrated longer recovery times in their stress responses than left HL people (Davidson, 2004). However, the role of HL as a moderator in the LE/hassles–distress relationship has not been tested, to the best of our knowledge. The aim of this research was to investigate whether HL moderated this relationship. Left HL people may be more immune to the effects of LE or hassles because of their approachoriented coping, thus enabling them to deal and possibly solve (controllable) daily problems. In addition, left HL people are higher on positive affect and lower on negative affect, which may render them less prone to emphasize and ruminate about past LE. Thus, we hypothesized that in left HL people, the LE/hassles– 48

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distress relationship will be weaker than that in right HL people. This hypothesis was examined in two separate correlation studies and in one experimental study, using different methodologies, which enabled us to examine the robustness of this effect. Since there are known gender differences in mental distress (Galanakis, Stalikas, Kallia, Karagianni, & Karela, 2009) and known gender differences in capacities related to HL (Andreano & Cahill, 2009), we statistically controlled for the effects gender. This study extends past studies by testing a neuroscience-based protective variable (moderator), namely HL, in the relation between LE and distress. It could shed light on a resilience factor in this relationship.

Study 1 Study 1 investigated the moderating role of HL in the relationship between students’ daily hassles and their distress. Method Participants Ninety business students at the IESEG School of Management, France, and Hogeschool-Universiteit Brussel, Belgium, voluntarily took part in this study, as part of their learning of the topic of stress management and organizational behaviour. The mean age was 21.26 (SD = 1.44). This study was approved by the authorities in the both universities. Measures Background information This included participants’ age and gender, and the hand they write with, as a proxy index of handedness. Hemispheric lateralization Hemispheric lateralization was measured with the Hemispheric Preference Test (Zenhausern, 1978). This 20-item questionnaire includes 10 items purportedly assessing left HL tendencies (e.g. being logical, having a business approach, planning and being structured) and 10 items purportedly assessing right HL tendencies (e.g. being artistic, remembering one’s dreams and explaining things by visual presentation), on a scale from 1 (never/not at all) to 10 (always/extremely). This scale is the only paper-and-pencil HL measure that has been validated against objective electroencephalography measures of HL (Merckelbach, Muris, Pool, DeJong, & Schouten, 1996). In the present study, the internal reliability of the left HL items was low (Cronbach’s α = 0.55), whereas that of the right HL items was adequate (Cronbach’s α = 0.70). The total of right HL scores was subtracted from the total left HL items, with higher scores reflecting left HL. Daily hassles Daily hassles were assessed with the Everyday Problem Scale (Burks & Martin, 1985). This is a 34-item Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

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scale on which respondents check any problem they experienced during the past 2 months. The endorsed problems are summed, with higher scores indicating a greater number of everyday problems. This scale significantly correlates with psychiatric symptoms, independent of major LE (Burks & Martin, 1985). Mental distress Mental distress was assessed using the 12-item version of the General Health Questionnaire (Goldberg et al., 1997). This scale assesses various forms of distress (worry, depressive symptoms, strain etc.) and the ability to deal with daily difficulties (e.g. self-efficacy and overcoming difficulties). Each item is scored on a 0–3 scale where 0 = never and 3 = always. After reversing the items that need reversal, the scores are summed. It has been validated against measures of depression (Goldberg et al., 1997). In the present study, the internal reliability was adequate (Cronbach’s α = 0.76). Statistical analyses We used partial Pearson correlations to test the association between daily hassles and distress, controlling for gender. To test for the moderating role of HL in this association, we grouped participants into the 40% who scored high (left HL) and the 40% who scored low (right HL) on the HL index. This enabled us to exclude participants with both unclear and non-differentiated HL. Since, in the literature, HL is normally considered a categorical variable (Hofman, 2008), we did not test its moderating role as a continuous variable but rather as a categorical one. Hence, the hassles–distress relationship was tested throughout this entire research separately in each HL subgroup. Since daily hassles were expected to be positively correlated with distress, mainly in the right HL group, we used a single tailed significance test and a p-value of 0.5). Although slightly weaker, this pattern of correlation remained similar when additionally controlling for our index of handedness (right HL: r = 0.27, p < 0.07; left Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

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Table I. Partial Pearson correlations between hassles and distress in the full sample and in each laterality group Variable In full sample Hassles In left HL people Hassles In right HL people Hassles

Partial r with distress* 0.24† 0.19 0.31†

HL: hemispheric lateralization *Partial r = controlling for effects of gender † p < 0.05, single tailed

HL: r = 0.18, p > 0.10). There were no significant differences between HL subgroups in mean distress levels [right HL = 28.23; left HL = 28.03; t(70) = 0.18, p > 0.5] or in hassles [right HL = 0.78; left HL = 0.72; t(71) = 0.99, 0.5, p > 0]. To rule out the possibility that this pattern of correlations resulted from different variances in right and left HL groups, we compared both HL subgroups on SD of hassles scores. No significant differences between right HL (0.22) and left HL participants (0.24) were found (p > 0.05). We also inspected the scatter plots of the hassles–distress correlation and found no clear outliners (data not showed). Discussion In the full sample, hassles were positively correlated with distress, and this remained when controlling for effects of gender. Furthermore, as hypothesized, only in the right HL but not left HL group were hassles correlated with distress. This is in line with the moderating role of left HL in the LE–distress relationship. However, all measures including HL that were used in the present study were self-report, and the observed results could be biassed by shared method variance. Thus, in study 2, we aimed to retest these results, using a neuropsychological measure of HL.

Study 2 Methods Participants This study was part of a larger study, whose complete details are published elsewhere (Bucks et al., 2008). Of the 80 participants, 42 were younger adults (mean age = 20.3, SD = 4.9 years), and 38 were older adults (mean age = 64.3, SD = 3.9 years). Younger participants were students at the University of Southampton, UK, whereas older adults were members of a study-participant pool at that university. Participants with self-reported major psychiatric conditions or dementia, chronic infectious illnesses, multiple sclerosis, Parkinson’s disease or cancer were excluded (the larger study was about cognition and the common cold). The 49

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study was approved by the School of Psychology Ethics Committee at the University of Southampton, and participants provided written informed consent. As in study 1, we only included the upper and lower 40% of participants on the HL measure for the analyses of the present study. Measures The hemispheric lateralization index This index was the identical index used in Gidron, Hall, Wesnes, and Bucks (2010), based on the cognitive drug research computerized assessment system (Wesnes, Ward, McGinty, & Petrini, 2000). The HL index was based on participants’ scores on pictorial recognition, which is associated mainly with right hemisphere frontal activation (e.g. Tsukiura et al., 2002) versus verbal word recognition, which is mainly associated with left hemisphere activation (e.g. Grady et al., 2003). For the pictures, participants first viewed 15 pictures, and after a delay, they were asked to recognize previously presented pictures out of 30; a similar procedure was performed for verbal recognition. We constructed a right HL index, with the following formula: Right HL = 100 × (%correct picture recognition %correct word recognition) / (%correct picture recognition + %correct word recognition). Thus, higher scores reflected greater pictorial versus verbal memory, reflecting better right compared with left hemisphere functioning, respectively. In the study by Gidron et al. (2010), the right HL index was significantly correlated with general IQ scores and with age, and men scored higher on right HL than women, supporting the preliminary validity of the right HL index and in line with past studies on gender (Andreano & Cahill, 2009) and age (Bugaiska et al., 2007). Life events This was assessed by a brief five-item scale, which asked participants whether they experienced in the past year stressful events in the domains of home, work, friends, legal and health (Roberts, Cox, Reintgen, Baile, & Gibertini, 1994). Each item is scored on a 0–10 scale in relation to its level of stressfulness. In the present study, the internal reliability coefficient was low (Cronbach’s α = 0.48). Distress This was assessed by the Hospital Anxiety and Depression Scale (Zigmond & Snaith, 1983). This scale is a commonly used instrument for the rapid assessment of anxiety and depressive symptoms. It includes 14 items: seven for anxiety and seven for depression, scored on a 0–3 scale. In the present study, the internal reliability coefficient for the anxiety subscale was Cronbach’s α = 0.71, and that for the depression subscale was Cronbach’s α = 0.58. 50

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Statistical analysis This followed the same steps as in study 1. Results We only included the upper and lower 40% of participants on the HL measure. The final sample included 65 participants (M = 41.6, SD = 22.5 years); 24.65% were men. Mean scores and standards deviations of anxiety and depression scales were M = 4.6 (SD = 2.7) and M = 2.0 (SD = 1.7), respectively. Mean score of LE scale was 16.3 (SD = 6.4), and the mean score of the neuropsychological HL index was 7.7 (SD = 7.7). Table II depicts the correlations between LE and anxiety and depression, for the full sample and for each HL subgroup, controlling for gender. As can be seen, in the total sample, LE were significantly positively correlated with both anxiety and depression. Furthermore, LE were significantly positively correlated with both anxiety and depression only in right HL and not left HL participants, controlling for gender. Similar to study 1, no significant differences in mean and SD of LE were found between left HL (16.6 +/ 5.4) and right HL (16.0 +/ 7.3) participants (all p > 0.05). Discussion Study 2 showed that in the total sample, LE were significantly and positively correlated with anxiety and depression, independent of gender. When examining these relationships separately for left and right HL, only in right HL, LE were consistently related to anxiety and depression, although this also occurred for LE and depression in the left HL subgroup. These results partly mirror those of study 1. This issue will be discussed in depth in the section on General Discussion. The previous two studies used a correlation design. It would be interesting to investigate whether left HL moderates experimentally induced distress. This was the aim of study 3.

Study 3 Given the results from studies 1 and 2, we expected that right HL participants would demonstrate stress responses to an experimentally induced stressor, whereas left HL participants would show weaker stress responses. #

Table II. Partial Pearson correlations between hassles and distress in the full sample and in each hemispheric lateralization group Variable LE in full sample LE in left HL LE in right HL

Anxiety *

0.31 0.06 0.58***

Depression 0.22* 0.37* 0.34*

Note: Partial correlations = controlling for effects of gender. LE: life events; HL: hemispheric lateralization *p < 0.05; ***p < 0.001, single tailed Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

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Method Participants This study was a part of a larger study on the effects of stress and HL on decision making, which included 206 university students (103 men and 103 women). In that study, half were exposed to a stressor, and half were not. In the present study, we focused just on the group exposed to the stressor. In the stress group, there were 97 participants (50 men and 47 women) whose mean age was 18.79 + 1.2 years. The study was approved by the Ethics Committee of the High University of Brussels. Measures Hemispheric lateralization Hemispheric lateralization was assessed by the prebisected line test (Harvey, Milner, & Roberts, 1995). In this test, 18 pre-bisected lines of different lengths are presented. In 15, the bisection is located in the centre of the line, whereas the in the other three, it is not, in order to increase participants’ motivation to perform the test. Participants must indicate which side is longer. Selecting the right side indicates left hemispheric utilization, whereas selecting the left side indicates right hemispheric utilization. We calculated a left HL index using the following formula: Left HL = 100 × [(Left Right) / (Left + Right)]. A similar test, the non-pre-bisected line test, was validated against electroencephalography measures of HL (Nash, McGregor, & Inzlicht, 2010). Stress response A 100-mm visual analogue scale was used to assess stress responses, with response options of 1 = no stress to 100 = extreme stress, following Sneed, Olson, Bubolz, and Finch (2001). Stressor For stress induction, we used an unsolvable anagram, where participants had to find as many words as possible in a rectangular word grid. It was impossible to locate the words. Such stressors typically induce temporary acute stress responses, physical and psychological (Dickerson & Kemeny, 2004). Controls (not described here) were asked to circle as many letters as possible (e.g. the letter A) in a similar letter grid. Both groups had a time limit for performing this task. Procedure and design An experimental randomized controlled design was used in this study. After participants provided their initial demographic information, they were evaluated for their levels of stress at baseline. Thereafter, they were randomly assigned either to the unsolvable stressor or to the controllable task (control) and then estimated once again their levels of stress using the visual analogue scale. Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

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Statistical analyses Participants were divided into left and right HL groups using a meaningful cutoff: Right HL scored below 0, and left HL scored above 0 on the HL index, as this related to the degree of HL. We then performed a mixed design ANOVA where the within-subjects factor was time and the between-subjects factor was left versus right HL. We examined a time × HL interaction, to test our hypothesis. Results The right HL group had a mean stress level of 3.44 + 2.12 before stress and a mean value of 5.53 + 2.28 after stress. In contrast, the left HL group had a mean stress level of 3.56 + 2.56 before stress and a mean value of 4.34 + 2.44 after stress. We then conducted the planned ANOVA, controlling statistically for effects of gender, which are known to influence HL and mood. As expected, a significant time × HL group interaction was found [F(1, 72) = 6.66, p < 0.05], as shown in Figure 1. Following this interaction, we found that time had a significant effect on stress levels in right HL participants [F(1, 41) = 27.28, p < 0.001] although time had no significant effect in left HL participants [F(1, 30) = 0.25, p > 0.05].

General discussion The aim of the present study was to identify a new possible moderator in the relationship between LE/hassles and distress. In the present research, the moderator was HL. In two separate correlation studies and one experimental study, using different research tools and in different cultures, we found consistency: In right HL participants, but not or to a lesser extent in left HL participants, LE/hassles were consistently positively correlated with mental distress (partialling out the effects of gender). In study 3, experimentally induced stress led to higher perceived stress in right HL but

Figure 1. Effects of time (pre-stress and post-stress) and hemispheric lateralization on perceived stress

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not left HL participants, substantiating the results of studies 1 and 2. In two of our studies, LE/hassles and distress were positively and significantly correlated in the full samples. These results support those of previous studies reviewed earlier (Billings et al., 1983; Blazer et al., 1987; Kendler et al., 1995; Kraaij et al., 2002; Murphy et al., 2000). However, HL emerged as a moderator in the LE/hassles–distress relationship. In both studies, this correlation was limited to right HL participants, concerning the outcome distress in study 1 and anxiety in study 2. These results are compelling when considering also the fact that they were observed, after controlling for gender and using different samples and methodologies: In study 1, HL was measured by a questionnaire, whereas in study 2, it was measured by a neuropsychological test, and study 3 used an experimental design to test this hypothesis. The only exception to this pattern was that in study 2, LE still correlated significantly with depression in people with left HL. We discuss this result in the succeeding text. Study 3 extended the results of our previous two studies by using an experimental design and another measure of HL. The results showed a lesser elevation of distress in the left HL group versus the right HL group, using a brief experimentally induced stressor. These results were obtained using the line bisection test for assessing HL. Although the line bisection test is a visual-motor task, scores on this test correlate with parietal and frontal brain activation (Nash et al., 2010). This result supports Davidson’s model of stress × diathesis (HL) concerning negative emotions (Davidson, 2004). How is it possible that people with a relatively left HL are more ‘immune’ to the effects of LE/hassles on mental well-being? Physiological and psychological explanations are plausible. Davidson (2004) reviewed several studies showing that people with right HL exhibit longer recovery times in physiological indices after stress, compared with left HL people. This may reflect a predisposition of right HL people to physiologically experience a longer stress response following exposure to stressors, which may over time be manifested by greater levels of distress given that physiological reactions such as sympathetic hyperactivity often accompany distress. The differential latencies of stress responses in right and left HL people resemble another moderator of reactivity, namely the autonomic nervous system. The right hemisphere primarily mediates the sympathetic response (Cerqueira, Osborne, & Sousa, 2008), whereas some evidence suggests that the left hemisphere mediates parasympathetic (vagal) activity (e.g. Wittling, Block, Genzel, & Schweiger, 1998). Furthermore, people with high vagal (parasympathetic) activity also recover more rapidly from acute stress in several physiological systems (Weber et al., 2010), similar to people with left HL. Thus, it is plausible that right HL participants may insufficiently modulate their physiological response to stress partly because of lower 52

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vagal and higher sympathetic activity, yet this requires future investigation. Alternatively, it is possible that right HL people may cope differently than their left HL counterparts. Indeed, right HL is associated with more withdrawal coping and with experiencing more distress (Hofman, 2008), reflecting the ‘behaviour inhibition system’ (Shackman et al., 2009). It is possible that by coping with LE or daily hassles via passive and avoidant coping strategies, daily hassles may remain unsolved and could then lead to experiencing greater mental distress (e.g. Chou, Chao, Yang, Yeh, & Lee, 2011). In study 2, left HL participants showed a significant correlation between LE and depression but not between LE and anxiety, whereas right HL participants showed significant correlations in both cases. We propose two explanations for the different patterns of correlations between LE and depression and anxiety, in left versus right HL people. A first explanation might be the unclear role of HL in depression. One study found that depression was related to right HL only if it was accompanied by certain anxiety symptoms (Engels et al., 2010). Other investigators also concluded that HL is inconsistently related to depression (He et al., 2010). The second possible explanation we propose is that another factor, namely anger/hostility, which was not assessed in our study, may have masked our ability to investigate the LE–depression relationship in each hemisphere. Different aspects of anger/hostility correlate with depression, which include anger in and anger out (Koh et al., 2002). However, anger in reflects the behaviour inhibition system, typically mediated by the right hemisphere, whereas anger out reflects the behaviour activation system typically mediated by the left hemisphere (Demaree, Everhart, Youngstrom, & Harrison, 2005). Furthermore, anger/hostility is positively related to LE (Smith, 1992). Thus, it is possible that both hemispheres contribute via different components of anger/ hostility to depression. This could have interfered in the LE–depression relationship in left versus right HL people. This issue requires further investigation. The main limitations of the present research include the use of a cross-sectional design in studies 1 and 2. Furthermore, it is highly plausible that bidirectional causality may exist in these results since mental distress may predispose people to experience, recall and report more LE or hassles. Nevertheless, study 3 used an experimental design, and its results concur with those of studies 1 and 2. However, study 3 only looked at immediate post-stress reactions. Future studies need to examine the pattern of results observed here, using a prospective study design. Although indeed our samples are not large, the mere fact of replicating the moderating (protective) role of left HL in three studies using different methodologies is a testimony for the possible reliability and validity of this new result. In addition, we did not assess approach or avoidance coping characteristics or physiological responses to stress, to uncover mechanisms possibly explaining the moderating Stress and Health 32: 47–54 (2016) © 2014 John Wiley & Sons, Ltd.

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role of left HL in the LE/hassles–distress relationship. Future studies should assess these factors as well. Finally, the concept of HL may be far more complex than imagined and consist of multiple dimensions (Liu, Stufflebeam, Sepulcre, Hedden, & Buckner, 2009), which some may moderate the effects of hassles more than other dimensions. Indeed, the HL–emotionality relationship appears to be stronger in temporal, prefrontal and parietal regions (Sutton and Davidson, 1997). Future studies should test whether the left HL protection of the effect of LE is specific to those specific regions. Another limitation is the low reliability of the HL measures in study 1. However, the consistency in the results using different HL measures in three studies provides evidence for the reliability of our results. In addition, since HL is related to positive affect (Davidson, 2004) and since positive affect is related to distress (Galanakis, Galanopoulou, & Stalikas, 2011), future studies should test whether HL mediates the moderating effects of positive affect on distress. REFERENCES Agelink, M. W., Boz, C., Ullrich, H., & Andrich, J.

Nevertheless, we observed a consistent mitigation by left HL of the effects of LE/hassles on experiencing mental distress, particularly anxiety and acute stress. Should our observed results be replicated, it is possible that left HL plays a protective role in the development of mental distress symptoms following exposure to LE or daily hassles. If correct, right HL people may benefit from learning coping strategies, i.e. problem-focused coping for controllable LE or emotion-focused coping for uncontrollable LE (Forsythe & Compas, 1987). Alternatively, people with right HL may benefit from cognitive exercises to activate their left hemisphere, in order to mitigate the effects of LE/hassles on their well-being. Such an approach needs to be tested in future studies. The results of these three studies bridge between the fields of neuroscience and stress and well-being and have both scientific and clinical implications.

Conflict of interest The authors have declared that they have no conflict of interest.

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