By KRISTIN JAVARAS
Published: August 6, 2014
Individuals with binge-eating disorder (BED) frequently have binge-eating episodes where they consume large amounts of food (e.g., at least two meals’ worth at once) while feeling like they can’t stop eating. In addition, individuals with BED don’t regularly compensate for eating by fasting, over exercising, vomiting, or using laxatives or diet pills – if they did, they would qualify for a diagnosis of bulimia nervosa rather than BED. In order to better understand what leads to binge-eating episodes, researchers have asked whether cues related to food (e.g., a picture of pizza, the word “pizza”) are processed differently, and perhaps preferentially, in the brains of people with BED. A recent paper in the journal Appetite by Svaldi and colleagues in Germany explored this question by examining whether women with BED are more likely to remember cues related to food.
Svaldi and colleagues compared 31 women with BED (who were, on average, in the obese BMI range) to 36 in the overweight or obese BMI range who had never had BED or any other eating disorder. (As a note, although individuals with BED are more likely to meet the criteria for being overweight or obese (i.e., BMI ≥ 25), it is not part of the diagnosis, and some individuals with BED are not overweight or obese.) Participants were asked to perform two tasks, one of which was the “recent-probes” task. In this task, participants were presented with a series of 34 trials seven separate times. The first two of the 34 trials were considered “warm up trials” and ignored when analyzing the results. Each trial consisted of being shown a blank screen, followed by a screen with a list of words (the “stimuli set”), followed by screens with numbers that participants had to classify as even or odd by pressing the right response key for even and the left response key for odd (the “filler task,” which is meant to prevent participants from repeating the words from the stimuli set in their head), finally followed by a “probe” word, which participants had to respond to by pressing the right response key if the probe was in the stimuli set for that trial and the left response key if it was not. All of the probe and stimuli set words were either food words (i.e., palatable foods, such as cake) or neutral words (i.e., office supplies, such as a stapler).
Trials could be classified as a “match” trial, in which the probe word appeared in the stimuli set for that trial, or a “non-match” trial, in which the probe word did not appear in the stimuli set for that trial. Trials could also be classified as a “recent” trial, in which the probe word appeared in the stimuli set for the previous trial, or a “non-recent” trial, in which the probe word did not appear in the stimuli set for the previous trial. In the figure shown below, Trial 5 is a non-match/recent trial. The probe word for Trial 5 (pizza) does not appear in the stimuli set for Trial 5 (scissors/cream/pen/fries), making Trial 5 a non-match trial. However, the probe word for Trial 5 (pizza) does appear in the stimuli set for the previous trial, Trial 4 (stamp/cake/ruler/pizza), making Trial 5 a recent trial. These non-match/recent trials might tempt the participant to incorrectly respond that the probe word did appear in the stimuli set for that trial, because they were remembering the word from the stimuli set in the previous trial. As a result, these non-match/recent trials were a bit complicated. Researchers compared how participants did on these difficult non-match/recent trials to how they did on the simpler non-match/non-recent trials, where it was easier to respond, correctly, that the probe word was not in the stimuli set because it hadn’t appeared recently (in at least the past 5 trials).
Researchers also looked at “interference scores:” the difference in performance on the more difficult non-match/recent trials versus the easier non-match/non-recent trials. Performance was measured by correct response time (i.e., how long it took the participant to correctly press the left response key to indicate a non-match), with faster response time representing better performance, and by errors (i.e., the percent of times the participant incorrectly pressed the right key to indicate a match), with fewer percent errors representing better performance. Since the non-match/recent trials are more difficult than the non-match/non-recent trials, one would expect participants to take longer to respond and make more mistakes on the former. A higher interference score suggests that the participant has been more distracted by the memory of words presented on recent trials. The researchers calculated the response time and error interference scores for food probe words only, and for neutral probe words only, to see if the type of word affected how much cognitive interference there was.
After examining the response data and removing unusually slow and unusually fast response times, researchers compared the response time and error interference scores for the women with BED to those from the women without BED. They found that women with BED had significantly higher response time interference scores than women without BED for food words. For neutral words, the average response time interference scores were slightly higher for the women with BED than the women without, but the difference was not statistically significant. The average error interference scores were also higher for women with BED for both food words and neutral words, but, again, the score difference between the groups did not achieve statistical significance.
Women with BED were almost as likely as women without BED to correctly indicate that a food word wasn’t in the stimuli set if they had seen it recently in the previous set, but it took them longer to do so. This suggests that they were more distracted by recent food words than women without BED. This finding could indicate that women with BED have a stronger memory bias for food cues than women without BED.
Of course, as the authors point out, correlation does not imply causation: the memory bias for food cues could be a cause or a consequence of binge eating (or both, or neither). For example, individuals for whom food is a more salient stimulus, as evidenced by a variety of traits, including memory bias, may be more likely to develop binge eating. Alternatively, the experience of binge eating may lead to a memory bias towards food cues. For example, if binge eating leads to increased shame and anxiety about food, individuals with BED may exhibit a memory bias towards food cues because negative emotion can sometimes enhance memory. One way to address this question is to follow individuals over time, beginning before they experience binge eating, to see if individuals with memory bias for food cues are more likely to initiate binge eating, and/or if the memory bias for food cues emerges subsequent to onset of binge eating.
Regardless of whether a memory bias for food cues contributes to the emergence of binge eating, it may contribute to its maintenance. A memory bias for food cues may make discontinuing binge eating a more difficult task. There are undoubtedly many ways to decrease this bias, but, given the aforementioned effect of emotion on memory, focusing on decreasing the intensity of emotion associated with food could be one place to start.
Svaldi, J., Schmitz, F., Trentowska, M., Tuschen-Caffier, B., Berking, M., & Naumann, E. (2014). Cognitive interference and a food-related memory bias in binge eating disorder. Appetite, 72, 28–36.