Decreased feedback learning in anorexia nervosa persists after weight restoration

Abstract

Objective: Anorexia Nervosa (AN) is a serious disorder, with a mortality rate the highest of any psychiatric illness. It is notoriously challenging to treat and mechanisms of illness are not well understood. Reward system abnormalities have been proposed across theoretical models of the persistence of AN. Feedback learning is an important component of how reward systems shape behavior and we hypothesized that individuals with AN would show poorer learning from feedback.

Methods: We administered the acquired equivalence task to measure both learning from incremental feedback and generalization of that learning to novel stimuli. Participants were individuals with AN (n = 36) before and after intensive weight restoration treatment and healthy comparison participants (HC, n = 26) tested twice. Performance was assessed as accuracy during the Learning and Test phases, for both trained and novel stimuli. The relationship between task performance and eating disorder severity at baseline was also assessed.

Results: Both before and after treatment, individuals with AN showed reduced learning from feedback in the Learning phase (F_3,180 = 2.75, p = .048) and lower accuracy during the Test phase (F_1,60 = 4.29, p = .043), as compared with HC. Individuals with AN did not differ from HC in accuracy for novel stimuli (F_1,60 = 1.04, p = .312), indicating no deficit in generalization. Decreased acquisition of feedback learning was associated with longer illness duration and with greater eating disorder symptom severity at baseline.

Conclusions: Individuals with AN show reduced learning from feedback or reinforcement, which may contribute to difficulties in changing maladaptive behaviors.

Keywords: acquired equivalence; anorexia nervosa; cognitive neuroscience; eating disorders; feedback learning; longitudinal; neuropsychology; reward.

Figure 1. Task structure and trial types

(A) In the Learning phase, participants learned a series of individual face-scene associations based on feedback (12 individual associations in total). A face-scene pair was presented on each trial, followed by performance-dependent feedback. (B) The Learning phase was followed by a Test phase, where participants received no feedback and were asked to respond to both previously experienced (Trained) trials and novel untrained face-scene association (Generalized) trials. (C) The Learning phase had three event types: Individual associations shared overlapping features such that two faces always were associated with a common scene (i and ii), and one of those faces was also associated with a second scene (iii). A scene that was the incorrect choice for one face was the correct choice for another face, such that simple stimulus-response learning strategies could not support learning. In the Test phase, novel associations (iv, Generalized trials) were presented intermixed with trials that tested knowledge for previously trained associations (Trained trials).

Figure 2. Acquired Equivalence Task Performance

(A) In the Learning phase, AN showed significantly decreased learning compared with HC (F(3,180)=2.75, p=0.048). Shown is performance collapsed across Sessions 1 and 2, as there was no effect of Session. (B) Accuracy in the Test phase was significantly lower for AN than HC (F(1,60)=4.29, p=0.043). As expected, participants were more accurate for the Trained trials than for the novel Generalized trials (F(1,60)=97.23, p < 0.001). The interaction was not significant, indicating that AN were impaired on both trial types, without a specific impairment in Generalization. (C) To account for baseline learning, groups were compared on Generalized trials divided by Trained trials; they did not differ significantly (F(1,60)=1.04, p=0.312). HC=healthy controls; AN=anorexia nervosa.

Figure 3. Task Performance and Clinical Severity

(A) Accuracy in the learning phase was significantly associated with the Eating Disorder Examination Questionnaire (EDE-Q) global score at Session 1 (ρ(34)=–0.50, p=0.002). (B) Accuracy in the learning phase was also associated with duration of illness (ρ(34)=–0.35, p=0.037) but this correlation did not reach the threshold of significance when correcting for multiple comparisons. AN=anorexia nervosa.