Decreased self-reported arousal in schizophrenia during aversive picture viewing compared to bipolar disorder and healthy controls
Introduction
Schizophrenia (SCZ) and bipolar disorder (BD) are severe mental disorders with an onset in young adulthood and overlapping clinical characteristics including: a shared propensity towards psychotic symptoms, mood symptoms (Romm et al., 2010) and neurocognitive dysfunction (Simonsen et al., 2009). Recent findings have also indicated the presence of overlapping risk genes which suggest a common underlying neurobiology (Purcell et al., 2009). The strict diagnostic division of severe mental disorders into SCZ and BD has thus been questioned (Craddock and Owen, 2010). In line with this notion of a dimensional rather than a categorical distinction between BD and SCZ, studies indicate that BD patients with a history of psychosis have the same patterns of cognitive deficits as patients with SCZ; however, BD patients without psychotic symptoms appear to function at the same level as healthy controls (HC) (Simonsen et al., 2010).
The central role of emotion in SCZ is apparent from Kraepelin's inclusion of flat affect in his first description of dementia praecox, and from Bleuler's original definition of SCZ as a disorder characterized by the splitting of thoughts from emotions. While it is clear that cognitive dysfunction plays a central role in SCZ and has clear links to social functioning (Green et al., 2005), the role of emotional dysfunction is less studied. Recent studies have indicated that the deficits in emotion processing in SCZ may have significant links to clinical symptoms and social functioning (Kee et al., 2003, Kee et al., 2009). However, the mechanisms behind emotion processing deficits in SCZ are still not fully understood.
Problems with the processing of emotion are regarded as a core deficit of BD (Clark and Sahakian, 2008). While the prognosis for BD is considered to be more favorable than that for SCZ, BD patients often have persistent alterations of psychosocial functioning (Treuer and Tohen, 2010), which may in part be linked to abnormal emotion processing. The persistence of trait-related changes through periods of remission, coupled with two distinct mood polarities with state-related changes complicates the study of emotional processing deficits in BD. This may be one of the reasons why there are so few studies investigating this area of BD and why the underlying mechanisms remain poorly understood (Phillips, 2006).
In clinical research the terms “affect” and “emotion” are often used interchangeably, but in affective neuroscience the former is used to refer to feeling states, while the latter refers to multiple components including expression, experience and physiology (Kring and Moran, 2008). Emotion processing is often measured by the International Affective Picture System (IAPS) (Lang et al., 1995), which uses pictures to elicit emotion from the participant, and then asks them to rate either the stimulus quality or the feeling elicited in response to the stimulus (Kring and Moran, 2008). The stimulus is rated on its perceived valence (pleasant–unpleasant) and on the ensuing arousal (low–high) (Lang et al., 1995). While women do not differ in reports of experienced emotion compared to men, they are more expressive and demonstrate different patterns of skin conductance during their response (Kring and Gordon, 1998). This should be taken into account in studies of emotional processing (Caseras et al., 2007, Kemp et al., 2004, Klein et al., 2003). Previous studies have also indicated that older adults perceive negative pictures as both more negative and more arousing than young adults (Gruhn and Scheibe, 2008).
A recent review conclude that IAPS is a good method for defining specific responses to stimuli in different mental disorders, including mood disorders and SCZ (Jayaro et al., 2008). Findings indicate that also individuals with SCZ are able to provide reliable and valid reports of emotional experience and emotion-related symptoms, and have representations of emotion that are reflected in the same 2-dimensional structure (valence and arousal) as in HC (Kring and Moran, 2008). The systematic investigation of emotional responses in BD is, however, in its early phases (Johnson et al., 2007).
Existing studies of emotion processing in SCZ are small, based on predominately male samples (Hempel et al., 2005, Hempel et al., 2007), and often exclude images with possible offensive content (Herbener et al., 2008). The majority of studies report no difference in valence or arousal between SCZ and healthy controls (HC) (Heerey and Gold, 2007, Hempel et al., 2005, Hempel et al., 2007, Herbener et al., 2008, Rockstroh et al., 2006). However, one recent study found lower valence, but not lower arousal ratings in SCZ compared to HC (Dowd and Barch, 2010). When aversive pictures were included, valence ratings were similar, but lower arousal was reported in the SCZ group (Burbridge and Barch, 2007, Curtis et al., 1999, Horan et al., 2010, Sander et al., 2005). This was especially the case when the aversive pictures had a social content (Sander et al., 2005).
A recent meta-analysis found little evidence of deficits in SCZ patients' ability to experience pleasurable emotional states (Cohen and Minor, 2010). In line with this finding, there is support for involvement of separate brain structures in the processing of positive and negative emotions (Silver et al., 2002). This raises the possibly that it is mainly the processing of negative affect that is impaired in SCZ. The finding of the meta-analysis could also be explained by a difference in the perception of socially threatening situations in SCZ compared to HC (Green and Phillips, 2004). A dysfunction in the processing of both social and negative stimuli may be part of a specific problem in social cognition in SCZ (Penn et al., 2008).
Existing studies of emotion processing in BD are scant, use small samples, have not included analysis of both genders or have not included reported arousal.
A recent study using IAPS found higher valence ratings of positive pictures for BD patients in hypomanic or manic states compared to HC (Bermpohl et al., 2009). Other studies found that BD patients in remission assess neutral images as more pleasant (Giakoumaki et al., 2010, M'Bailara et al., 2009) or with higher level of arousal than HC (M'Bailara et al., 2009). A study of euthymic male children/adolescents with BD found that there were no differences in the valence ratings of IAPS pictures between BD and HC (Chang et al., 2004), while a study of the siblings of patients with BD rated negative stimuli as more negative than HC (Giakoumaki et al., 2010).
Studying emotion processing across SCZ and BD offers a potential for identifying shared and illness-specific allied phenotypes in these disorders (Hill et al., 2008). However, to our knowledge no previous study has investigated the differences and similarities in emotional processing between HC, BD and SCZ. The current study includes a large sample of male and female patients with SCZ and BD in a stable phase of the illness as well as HC subjects drawn randomly from the same recruitment area.
This study aims to answer the following research questions:
- (i)
To what extent do patients with SCZ, patients with BD and HC show different patterns of emotional response (i.e. reported valence and arousal to the IAPS pictures) to neutral and aversive stimuli?
- (ii)
To what extent do other individual characteristics such as age, gender and a history of psychosis, rather than diagnostic group influence emotional response?
We hypothesized that patients with SCZ would report lower arousal for aversive and, in particular, socially aversive pictures compared to BD and HC, and that patients with BD would report higher arousal to neutral pictures than SCZ and HC.
Section snippets
Sample
The Regional Committee for Medical Research Ethics and the Norwegian Data Inspectorate approved the study, and participants' written, informed consent according to the Declaration of Helsinki was obtained. Patients are participants in the ongoing Thematically Organized Psychosis (TOP) Study consecutively recruited from the outpatient and inpatient units of the three major hospitals in Oslo, Norway from July 2004 through May 2009. Inclusion criteria for the 212 patients were: Age between 18 and
Valence
In the repeated measures ANOVA there was a large main effect of valence evaluation (Wilks' Lambda 0.18, F(2, 343) = 8.03, p < 0.005, partial eta squared 0.82), with mean ratings of aversiveness lowest for neutral pictures, second highest for non-social aversive and highest for social aversive pictures in all three participant groups. There was no main effect of diagnostic group on the ratings of aversiveness, F(2,344) = 0.33, p = 0.71, partial eta squared 0.002, but a small but significant interaction
Discussion
The main finding of this study is the interaction between diagnostic group and level of emotionally evocative stimuli on subjective ratings of valence and arousal. While patients with SCZ report higher arousal for neutral stimuli compared to the other groups, they report lower arousal for increasingly aversive stimuli. The HC group on the other hand reported the lowest group-level arousal for neutral stimuli with a steeper increase for increasingly aversive stimuli than the other groups. The BD
Acknowledgements
In addition to the clinicians who contributed to patient recruitment, we would particularly like to thank the participants in the TOP study for their contribution. A special thanks to Kjetil Sundet, Christine Lycke Brandt, Eivind Bakken, Merete Øibakken, Mona Kolstø Otnæss, Ragnhild Storli, Thomas Bjella and Greg Reckless.
The study is funded by the Research Council of Norway (Grant # 181831) and the South-Eastern Norway Health Authority (Grants # 2004123, 2006258 and 20079069). Neither had any
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