On Weight and Waiting: Delay Discounting in Anorexia Nervosa Pretreatment and Posttreatment

Abstract

Background: Individuals with anorexia nervosa (AN) override the drive to eat, forgoing immediate rewards in favor of longer-term goals. We examined delay discounting and its neural correlates in AN before and after treatment to test a potential mechanism of illness persistence.

Methods: Inpatients with AN (n = 59) and healthy control subjects (HC, n = 39) performed a delay discounting task at two time points. A subset (n = 30 AN, n = 22 HC) participated in functional magnetic resonance imaging scanning during the task. The task consisted of a range of monetary choices with variable delay times, yielding individual discount rates-the rate by which money loses value over time.

Results: Before treatment, the AN group showed a preference for delayed over earlier rewards (i.e., less steep discount rates) compared with HC; after weight restoration, AN did not differ from HC. Underweight AN showed slower response times for earlier versus delayed choices; this reversed with treatment. Underweight AN showed abnormal neural activity in striatum and dorsal anterior cingulate; normalization of behavior was associated with increased activation in reward regions (striatum and dorsal anterior cingulate) and decision-making regions (dorsolateral prefrontal cortex and parietal cortex).

Conclusions: The undernourished state of AN may amplify the tendency to forgo immediate rewards in favor of longer-term goals. The results suggest that behavior that looks phenotypically like excessive self-control does not correspond with enhanced prefrontal recruitment. Rather, the results point to alterations in cingulostriatal circuitry that offer new insights on the potential role of abnormalities in decision-making neural systems in the perpetuation of AN.

Keywords: Anorexia nervosa; Decision-making; Delay discounting; Eating disorders; Imaging; Longitudinal.

Figure 1. Delay discounting task design

Individuals are presented with a choice between a smaller amount of money available sooner (SS) and a larger amount available later (LL). Amounts ranged from $15 to $85 and time of delivery for SS choices was either Now or in 2 weeks, and the time of delivery for LL was 2 or 4 weeks after the SS. Outside the scanner, there was no time limit for responding. In the fMRI version, there was a fixation cross between trials. All task parameters (i.e. monetary values, time differences) were the same inside and outside the scanner.

Figure 2. Individuals with AN have lower discount rates than HC only when underweight

(A) The log-transformed discount rates (per unit years) are shown for individuals with AN and HC at Sessions 1 and 2. Lower log-transformed discount rates indicate less steep discounting, i.e., a preference for larger-later over smaller-sooner options. (B) The proportion of trials that the larger-later option was chosen is shown for the AN and HC groups at each Session, separated into three bins indicating how much greater the larger-later choice was than then smaller-sooner choice in percentage terms. The AN group shows an overall decrease in the proportion of trials that they chose the delayed option, rather than for a specific subset of trials. ^a Session 2 sample size (N=31 HC, 43 AN) ^* p<0.05 (error bars are SEM).

Figure 3. Individuals with AN chose smaller-sooner options more slowly than larger-later options when underweight, and switched when weight restored

(A) Response time by percent that the larger-later (LL) option is greater than the smaller-sooner (SS) option. This shows that both groups quickened their responses across session, and for some trial types more than the other. (B) Response time by session, split by SS and LL choice. The AN group shows a significant switch from being slower during SS than during LL choices when underweight, to being faster during SS than during LL choices once weight restored.

Figure 4. Individuals with AN have altered neural activity as compared with HC for larger-later (LL) versus smaller-sooner (SS) choices in cingulo-striatal and fronto-parietal circuitry

(A) Areas with a significant interaction effect of Choice (LL or SS), Diagnosis (AN or HC), and Session (1 or 2) (whole-brain corrected p<0.01, individual voxel threshold p<0.01, spatial extent >= 41 voxels; see Table S9 in the Supplement). (B) Mean contrasts of LL minus SS choice neural activity between Diagnosis (AN or HC) and Session (1 or 2) in regions identified in the interaction effect. A positive value indicates greater neural activity when making LL choices than when making SS choices. ^a Session 2 sample size (17AN, 14HC). ^# p<0.10, ^* p<0.05, ^** p<0.01, ^*** p<0.001 (error bars are SEM) Symbols below the horizontal bar indicate the test of the LL-SS contrast, those above indicate t-tests between diagnostic group of this contrast (Table S10 in the Supplement).