Delay discounting abnormalities are seen in first-episode schizophrenia but not in bipolar disorder
Introduction
In a digital age where many things can be obtained instantly, it is becoming difficult to resist an immediate reward and wait for a larger payoff in the future. The propensity to discount future rewards as a function of time is called delay discounting (Kirby, 1997). DD is considered one dimension of impulsivity and closely linked to other dimensions such as self-report impulsivity (MacKillop et al., 2016; de Wit et al., 2007). Individual differences in DD are argued to be a stable, trait-level feature (Horan et al., 2017; Kirby, 2009) which is often associated with cognitive functions, such as working memory capacity and intelligence (Shamosh et al., 2008). These intertemporal choices are suggested to be modulated by a competition between two interacting systems, with the limbic system biased towards immediate payoffs while the lateral prefrontal cognitive control system favors more future-oriented goals achieved through self-control (Figner et al., 2010; McClure et al., 2004; Volkow and Baler, 2015).
Given the systems subserving intertemporal choices, schizophrenia patients (SZ) who show impaired cognitive functions, such as working memory maintenance (Cohen et al., 1999) as well as diminished motivation towards receiving distant reward (Barch and Dowd, 2010; Gold et al., 2008), would be expected to also show abnormalities during delay discounting, presumably through a bias towards immediate choices. Indeed, a number of studies have found that chronic SZ patients showed steeper discounting in the form of higher discounting rate (k; Ahn et al., 2011; Brown et al., 2018; Heerey et al., 2011; Heerey et al., 2007; Weller et al., 2014; Yu et al., 2017). The discounting rate is derived from a hyperbolic model in which the present value of a future reward is inversely proportional to the delay as well as the k (Kirby, 1997; but see alternative models e.g. McClure et al., 2004). Therefore higher k indicates steeper discounting and more impulsive decision-making. Elevated discounting rates in SZ have been found to be correlated with lower working memory capacity (Ahn et al., 2011; Brown et al., 2018; Heerey et al., 2007), verbal reasoning (Yu et al., 2017) and the ability to forecast future events (Heerey et al., 2011), further linking cognitive impairments to DD. Nevertheless, a number of studies reported no DD difference between chronic SZ and healthy controls, making it difficult to make a definitive statement about DD in chronic SZ (Avsar et al., 2013; MacKillop and Tidey, 2011; Wing et al., 2012). Presumably, the susceptibility of DD to contextual influences such as incidental episodes of affective state (Lempert and Phelps, 2016) may help explain some of the inconsistencies.
On the other hand, there is substantial evidence showing that schizophrenia spectrum disorders share genetic and symptom overlap with bipolar disorder (Cardno and Owen, 2014; Craddock et al., 2009; Lee et al., 2013; Lichtenstein et al., 2009), which may offer an interesting comparison group that is particularly characterized by hypersensitivity for reward as well as a diminished ability for self-control (Reddy et al., 2014; Swann et al., 2009; Whitton et al., 2015). These characteristics also tend to be associated with adverse consequences such as substance abuse (American Psychiatric Association, 2013; Swann et al., 2003) and are theoretically linked to more impulsive decision-making and steeper discounting. In particular, both SZ and BP show elevated trait impulsivity across multiple dimensions (Fortgang et al., 2016), which are correlated with brain structural differences at orbitofrontal cortex (Nanda et al., 2016). Studying DD abnormalities across SZ and BP could help further our understanding of impulsive decision making across diagnostic boundaries.
Interestingly, a limited number of studies investigating DD in BP showed mixed results. Following the seminal work of Ahn et al., 2011 showing steeper discounting in chronic BP, a recent study failed to replicate the finding (Brown et al., 2018). It was argued that this null finding was predominantly driven by a depressed sample of BP patients. Despite the suggestion that manic and depressive mood states tap into different aspects of impulsivity (Swann et al., 2008), it is not clear how they may differentially influence intertemporal decision-making (i.e., DD). Along this line, one study using individuals at risk for mania reported no DD differences relative to HC (Meyer et al., 2015). Interestingly, using an adolescent sample, Urosevic and colleagues found that BP patients did not show age-related DD improvements (older individuals are more able to wait for a larger reward) as observed in controls (Urosevic et al., 2016), highlighting potentially different developmental trajectories across the two groups.
The majority of the published literature focuses on DD in chronic SZ and BP. At earlier stages of illness, more proximal to the first episode, one hopes to minimize influences that are secondary to the illness (e.g., chronic medication effects, years of substance use, metabolic syndrome) which could serve as a first step addressing the inconsistencies among the previous DD findings. Furthermore, impulsivity is related to clinical symptoms in SZ and BP (Nanda et al., 2016), and DD specifically is associated with real-world impulsive behaviors (Reimers et al., 2009). A better understanding of DD process in SZ and BP would provide valuable information to clinical practice, especially for FE patients where early intervention is associated with better treatment outcomes (McFarlane et al., 2014). To our knowledge, no study has reported DD using a FE sample with both SZ and BP with psychotic features, as we do in the current study. Two versions of DD tasks were tested, the Kirby Monetary Choice Questionnaire following previous work (Heerey et al., 2011; Heerey et al., 2007; Kirby et al., 1999; Meyer et al., 2015) and a version evaluating the decimal effect of DD in which each monetary offer was shown either in rounded or decimal values (Fassbender et al., 2014). These two versions were selected in order to test comparability to the existing literature using the Kirby version and to evaluate whether changes in presentation style of monetary offers (e.g. decimal numbers) would reduce impulsive choices in individuals with SZ and BP, as has been previously shown in individuals with attention deficit/hyperactivity disorder (Fassbender et al., 2014). We further anticipated higher discounting rates for SZ relative to HC across both DD tasks, which were expected to be associated with negative symptoms (Heerey et al., 2007; Kring and Barch, 2014). Finally, based on the established literature on increased impulsivity in BP (Reddy et al., 2014; Fortgang et al., 2016) we hypothesized that BP would also show increased DD relative to HC.
Section snippets
Participants
In total, there were 173 participants included in this study, including seventy-two SZ spectrum patients (49 schizophrenia, 20 schizoaffective disorder and 3 schizophreniform), twenty-eight euthymic BP patients with psychotic features, and seventy-three HC. All subjects provided written informed consent prior to their participation and the UC Davis Institutional Review Board approved all components of the current study.
All patients were recruited as outpatients through the Early Diagnosis and
Demographical and clinical
The three groups were not significantly different in age, gender and parental education (ps > 0.27; Table 1). As expected, HC had higher years of education than SZ (p < .001) and BP (p = .004). No difference was found between SZ and BP (p = .91).
Kirby DD
We first examined the two-way mixed model ANOVA with condition (small, medium, and large) and group (SZ, BP, HC) as factors. No group by condition interaction was found (F (4, 326) = 0.44, p = .78), although we did identify significant main effects of
Discussion
This study is the first to our knowledge that combined two versions of DD tasks to investigate intertemporal choice among FE SZ, BP and HC. We found that SZ patients at this stage of illness showed task-dependent abnormalities in discounting, which showed modest correlation with positive symptoms (uncorrected for multiple comparisons). Finally, BP did not differ from HC on any discounting measures, suggesting intact DD at early stage of the illness.
While we did find DD abnormalities in FE SZ in
Contributors
TAL, CF and CSC designed the study and wrote the protocol. HW managed the literature review. HW undertook the statistical analysis under the supervision of TAL and RJM, and HW wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript.
Role of the funding source
The funding agency had no role in creating the experiment or writing the manuscript.
Declaration of competing interest
The authors declare no conflict of interest.
Acknowledgements
We thank research assistants in the Imaging Research Center for assistance with data collection as well as our participants and their families for their time and effort. This work was supported by National Institute of Mental Health (5R01MH059883) to C.S.C.
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2022, Journal of Psychiatric ResearchCitation Excerpt :The difference between our samples and others may be due to mood state, both of these other studies (Ahn et al., 2011; Brown et al., 2018) evaluated individuals with BD who were predominantly in a symptomatic (e.g., depressive or emergent (hypo)manic) mood state). Two recent studies of delay discounting that were conducted among individuals with BD in a euthymic to borderline euthymic mood state found that discounting rates more closely resembled discounting rates in the comparison healthy control samples (Mellick et al., 2019; Wang et al., 2020). It is noteworthy that current delay discounting predicted the summary clinical risk composite score given that 3 out of the 5 variables that comprise this summary variable are lifetime (rather than current) variables, and may accord with prior work that has suggested discounting of delayed rewards is a trait-like characteristic (Odum, 2011).
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2021, Journal of Psychiatric ResearchCitation Excerpt :Concretely, the authors of this study observed that within the men subsample: a) the presence of GD was related with increased rates of delay discounting (compared with non-gambling); b) individuals with history of treatment for substances or poly-substances use registered higher delay discounting (compared with non-consumers); and c) this may suggest that men who exhibit schizophrenia with substance related problems could be characterized by higher levels in some impulsivity domains, that positive reinforcement mechanisms could play a smaller role in the addictive processes within schizophrenia populations (compared to other diagnoses), and that lower levels of these features could create sensitivity to addiction. But these results should be considered with caution: mixed findings have been obtained in studies assessing the role of delay discounting, and these inconsistent evidences could be explained by the occurrence of comorbidity in chronic samples (Wang et al., 2020). Therefore, further studies should assess how choice impulsivity varies across psychiatric disorders and comorbid conditions, including the pathways between delay discounting and clinical manifestations among GD with schizophrenia.
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2020, Schizophrenia ResearchCitation Excerpt :In contrast, frontal-striatal interactions favoring the latter would instead be biased toward immediate rewards, “risky” decision-making and increased impulsivity. Even though impulsivity is not a prominent clinical feature in schizophrenia (SZ), studies have consistently found that SZ patients (Ahn et al., 2011; Heerey et al., 2007; Wang et al., 2020) as well as their unaffected biological relatives (Ho et al., 2018) have higher discounting rates during DDT indicative of increased impulsive decision making. Additionally, steeper discounting in SZ patients has also been associated with cognitive deficits, including working memory (Ahn et al., 2011; Brown et al., 2018; Heerey et al., 2007) and verbal reasoning (Yu et al., 2017); further linking cognitive impairments to delay discounting.