Article Commentary: Is Obesity Linked with Episodic Memory Impairment? A Commentary on Cheke, Simons, and Clayton (2016)

In a recent paper published in the Quarterly Journal of Experimental Psychology, Cheke, Simons, and Clayton (2016) report a study investigating the link between Body Mass Index (BMI) and episodic memory. The study was motivated by two lines of argument. First, that obesity can lead to neurological changes that result in a decline in episodic memory function. Second, that episodic memory plays a role in regulating eating behaviour, and thus BMI. Fifty young participants were tested on a novel episodic memory task (termed the Treasure Hunt Task), and their BMI, age, level of education, and gender were recorded. Participants’ BMIs ranged from 18 to 51, and included lean, overweight, and obese individuals. Stepwise linear regression analyses were conducted to test whether BMI—or other factors—predict episodic memory performance. The authors interpreted their results as supportive evidence for the hypothesis that “individuals with higher BMI may exhibit a deficit in episodic memory relative to lean controls” (Cheke et al., 2016, p. 9). Due to the increased focus on obesity in western societies, the study has gained considerable media interest, with alarming titles such as “Obesity linked to ‘worse memory’” (BBC), or “Obesity linked to memory deficits” (The Guardian). However, three main aspects of the original article that seem premature based on the results published by Cheke et al. (2016) concern us—especially the proposed explanations of the BMI–memory link. The first issue is the memory task and its associated measures. An episodic memory “Treasure Hunt Task” was adopted from memory research on nonhuman animals. The task involved remembering what, where, and when objects were hidden in various scenes. The task can be decomposed into four measures: a WWW measure, which involves recalling the bound event representation (i.e., episodic memory), and independent what, where, and when measures, each based on a series of forced-choice recognition memory questions. In general, this task is based upon a conceptualization of episodic memory that is over 40 years old (Tulving & Donaldson, 1972; cited in Cheke et al., 2016) and omits the subjective recollective experience that Tulving (2002) himself and others (e.g., Conway, 2009) now hold as an indispensable marker. A well-established approach to measure episodic memory is through reports of subjective judgements of recollection as opposed to familiarity or knowing, which reliably discern the processes underlying long-term memory (Gardiner & RichardsonKlavehn, 2000). Moreover, considering the range of neurocognitive processes that plausibly contribute to over-eating, other aspects of cognition, especially executive function (e.g. inhibition, cognitive control), will be important to measure. Indeed, as executive functions are involved in the control of food intake (Davidson, Tracy, Schier, & Swithers, 2014; as cited by Cheke et al., 2016), experimental tasks measuring the ability to control memory, such as the process dissociation procedure (which distinguishes between recollection and familiarity as controlled and automatic components, respectively) (Jennings & Jacoby, 1997), might serve as a powerful paradigm for investigating differences in memory as a function of obesity. Finally, measuring the phenomenological characteristics of episodic memories (e.g. overall vividness, perceptual details, emotional valence), especially those related to food intake, could also help elucidate the role of memory in obesity. The second point of concern is the findings. To test their hypothesis, the authors analysed whether BMI