Research reportThe future is now: Comparing the effect of episodic future thinking on impulsivity in lean and obese individuals
Introduction
Obesity is due to energy intake in excess of energy expenditure (Hill, Melanson, & Wyatt, 2000), and is associated with chronic conditions such as cardiovascular disease, stroke and type-2 diabetes (Björntorp, 1990, Björntorp, 2009). Despite these well-publicized adverse outcomes (Winter & Wuppermann, 2013), many individuals often choose to overindulge in high energy-dense and unhealthy foods that result in a positive energy balance. One reason for the excess intake may be a preference for the immediate gratification of high energy-dense foods, as opposed to not consuming these foods to be healthy later. This discounting of larger future rewards in favor of smaller immediate rewards is known as delay discounting (DD) and it is greater as the temporal distance between the immediate and delayed rewards increases (Bickel & Marsch, 2001). Higher DD rates have been associated with substance abuse, problem drinking, smoking, pathological gambling, and risky HIV behaviors (Bickel and Marsch, 2001, Bickel et al., 1999, Kollins, 2003, Madden et al., 2011, Vuchinich and Simpson, 1998).
The inability to delay gratification or greater DD is also cross-sectionally and prospectively related to obesity (Davis et al., 2010, Francis and Susman, 2009, Weller et al., 2008). Higher DD predicts greater consumption of high energy-dense ready-to-eat and away-from-home foods in obese women (Appelhans et al., 2012). DD also interacts with food reinforcement to predict energy intake such that individuals with a high motivation to eat and high levels of DD consume more calories in ad libitum eating sessions (Appelhans et al., 2011, Rollins et al., 2010). Furthermore, the ability to delay gratification predicts success in weight loss treatment which suggests that modifying DD may improve behaviors related to weight loss (Best et al., 2012).
Individuals making impulsive decisions typically focus on the present and de-value future rewards signifying a shortened time perspective during inter-temporal decision making (Petry, Bickel, & Arnett, 1998). One approach to reducing the bias towards immediate gratification or DD is to vividly imagine the future during decision making using episodic future thinking (Benoit et al., 2011, Peters and Büchel, 2010). Episodic future thinking (EFT) is a type of prospective imagery that involves self-projection to pre-experience future events (Atance & O’Neill, 2001). EFT engages the episodic memory network; the memory system for autobiographical details, in mentally simulating the future (Atance and O’Neill, 2001, Schacter et al., 2007). It has been suggested that episodic simulation of the future steers decision-making towards long term benefits (Boyer, 2008) and EFT has been shown to reduce DD (Peters & Büchel, 2010).
We have shown that EFT reduces both DD (ES$10 = 1.44, ES$100 = 1.51, p = 0.017) and ad libitum energy intake (ES = 1.09, p = .011) in obese individuals in a tempting food situation (Daniel, Stanton, Epstein, & ePlease update reference ‘Daniel et al., in press). However, research suggests that obese individuals often show suboptimal functioning in certain brain regions that could lead to a blunted EFT effect in obese individuals (Volkow et al., 2008). Higher BMI is associated with decreased regional cerebral blood flow in the dorsolateral prefrontal cortex, anterior prefrontal cortex, orbitofrontal area and the anterior cingulate cortex (Willeumier, Taylor, & Amen, 2011). Deficits in these regions may limit EFT’s effectiveness as the dorsolateral prefrontal cortex and anterior cingulate cortex have been implicated in the EFT effect (Peters & Büchel, 2010).
Furthermore, the EFT effect is associated with increased neural interaction between the anterior cingulate cortex and the hippocampus (Peters & Büchel, 2010). Animal studies show that high-fat diets similar to those associated with obesity in humans, creates deficits in the prefrontal cortex and the ventral and dorsal hippocampus in rats (Kanoski, Meisel, Mullins, & Davidson, 2007). Research in humans indicates that some hormonal deficits associated with decreased hippocampal volume in pre-diabetics and type 2 diabetics (Bruehl, Wolf, & Convit, 2009) may be mediated by higher BMI (Ursache, Wedin, Tirsi, & Convit, 2012). In addition, elderly obese individuals show atrophy in the frontal lobes, anterior cingulate gyrus and hippocampus compared to elders with a normal BMI (Raji et al., 2010). This converging evidence suggests that the neural deficits related to obesity may lead to a reduced EFT effect in obese compared to lean individuals. Thus, the main aim of the present study was to compare the effect of EFT versus a control imagery task on DD in non-overweight and overweight/obese women. We used a within subject design as opposed to the between design used in our previous study (Daniel, Stanton, Epstein, & ePlease update reference ‘Daniel et al., in press). We examined differences in the magnitude of change in DD due to EFT between lean and obese individuals.
There are individual differences in the magnitude of change in DD as a function of EFT. Identification of traits that moderate the effect of DD may provide insight into who may benefit the most from EFT. As EFT targets a temporal bias toward immediate rewards, trait level temporal orientation (Henson et al., 2006, Zimbardo and Boyd, 1999) may be related to responsiveness to EFT. Behavioral inhibition, the sensitivity to punishment and novelty; and behavioral activation, the sensitivity to reward and motivation for goal-directed activity (Carver & White, 1994), have been associated with delay of gratification (Corvi et al., 2012, Davis et al., 2007) and overeating (Davis et al., 2007). Sensitivity to reward and individual’s motivation for goal directed activity may influence responsiveness to EFT.
Section snippets
Participants
Lean (Body Mass Index (BMI = kg/m2) <25, N = 24) and overweight/obese (BMI ⩾ 25, N = 24) women between the ages of 18 and 40 were recruited for the study. Thirty-three percent of the participants were minority, 44% were high school or vocational graduates, with 56% of participants with at least some college. Women were recruited through a laboratory database, flyers posted around the University at Buffalo campus, community settings and web-based advertisements. Participants were screened by telephone
Results
Participants’ rated frequency and vividness of EFT imagery (4.45 ± 0.75) higher than CET imagery (3.95 ± 0.81), (F(1, 46) = 18.36, p < 0.001, ES = 0.61) during the DD task and this difference in imagery was entered as a covariate in future analysis. ANCOVA showed a main effect of condition (F(1, 46) = 8.96, p = 0 .004, ESd$10 = .32, ESd$100 = .50), controlling for differences in imagery during the DD task. There were higher AUC values in the EFT condition compared to the CET condition for both $10 (0.70 ± 0.26 vs.
Discussion
This experiment replicated the effect of EFT reducing DD (Daniel et al., in press) using a within-subject design. Despite the suggested neurophysiological differences between lean and obese individuals that relate to the EFT mechanism, we found no differences in the effectiveness of EFT between lean and obese individuals. Given that EFT works with overweight/obese women as well as normal weight women, and DD is associated with higher energy intake, obesity and less success in obesity treatment (
Acknowledgements
We appreciate Shirin Aghazadeh, Travis Stewart and David Lowry for assisting with data entry, and Katelyn Carr and Henry Lin for feedback on study design. This research was funded in part by Grant 1U01 DK088380 from the National Institute of Diabetes and Digestive and Kidney Diseases to Dr. Epstein.
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