How CANTAB can help to understand cognition in eating disorders

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2 March 2023

How CANTAB can help to understand cognition in eating disorders

During Eating Disorder Awareness Week (27th February - 5th March), Hannah Hickinbotham and Eleanor Rist reflect on the evidence around how cognition is affected in eating disorders, and how CANTAB® can be used for research in this area.

Around 1.25 million people live with an eating disorder in the UK¹. There are many types of eating disorder, including:

Other Specified Feeding or Eating Disorder (OSFED): A category of eating disorders where the individual doesn’t meet the full criteria for an eating disorder. These may include atypical anorexia (psychopathology present, but their BMI > 18.5kg/m²) subthreshold bulimia nervosa or binge eating disorder (lower frequency of behaviours than once a week for 3 months), amongst others². This is the most common type of eating disorder, accounting for about 47% of cases.
Binge Eating Disorder (BED): This is characterised by frequent binge eating (eating a large amount of food in a given time period and feeling out of control while doing so). However, these binges are not followed by the inappropriate compensatory behaviours seen in bulimia nervosa as described below. BED is the second most common type of eating disorder, accounting for around 22% of cases.
Bulimia Nervosa (BN): Characterised by frequent binge eating episodes, like in BED, followed by mechanisms to compensate for this bingeing, such as self-induced vomiting, laxative misuse, excessive exercise, and fasting. Additionally, those living with BN often base their evaluation of themselves on their weight and shape². BN accounts for around 19% of eating disorder cases.
Anorexia Nervosa (AN) is characterised by restricting food intake relative to the individual’s requirements, causing low body weight, as well as an intense fear of weight gain or being “fat”. People with AN can often perceive their bodies to be larger than they are, and similarly to BN, may heavily base their self-esteem on the weight, size and shape of their body². AN accounts for around 9% of eating disorder cases in the UK.

Eating disorders are complex mental health conditions, which cause severe mental, physical, and psychosocial impairments. Research has implicated a potential link between neurocognitive deficits and the psychopathology that is observed in, and maintains, an eating disorder. An area of cognition that is particularly affected is executive functioning, an adaptive process which allows individuals to process information and behaviours based on their goals.

Within eating disorder research, executive functioning can be split into 3 domains: inhibition and interference control, working memory, and cognitive inflexibility³. Current eating disorder research is based on a neurological deficit-based model and has focused on specific domains rather than a comprehensive review or focus on distinct types of eating disorders⁴. This may reflect a diversity in cognitive impairment in eating disorders, or the under-research of cognition in eating disorders in comparison to other mental health conditions.

Areas of research interest

Below, the current areas of research are highlighted for the various eating disorders.

BED:

Poor inhibitory control and cognitive flexibility: this impairment has been linked to the over-consumption of particular foods, especially after a period of acute restriction. Individuals may also struggle with problem-solving, strategy implementation, therapeutic engagement, and planning. These can become increasingly difficult and problematic behaviours⁵.
Decision-making impairments: along with poor working memory, impaired decision-making may lead individuals to feel overwhelmed when a binge urge arises, making it more difficult to remember the negative consequences and emotions, leading to impulsive behaviours and a sense of lack of control.
An altered attention bias: in comparison to healthy controls (HC), individuals with BED have demonstrated an increased attention bias to food-related stimuli, and struggle to alter this hyperfocus. However, it is unclear whether this is due to a reaction of hypervigilance around food or a preoccupation⁴.

BN:

An altered attention bias: eye tracking research has demonstrated that individuals with BN and AN avoid images of food and overweight and obese people, and focus towards images of people with a low BMI, showing a difficulty in disengagement from these images^6,7.
Inhibitory control: individuals with BN show difficulty in withdrawing inappropriate motor responses, particularly when presented with food or shape-related stimuli, demonstrating the impulsive nature of the compensatory behaviours associated with BN⁷.
Central coherence: this refers to the process of taking detailed information and integrating it to form a bigger picture, which has been shown to be a reduced ability in those with BN⁴.

AN:

Poor set-shifting: also known as cognitive flexibility, individuals with poor set-shifting struggle with problem-solving or changing scenarios due to rigid thoughts.
Poor central coherence: individuals with AN have a detail-focused mindset, struggling to see things on a whole. This links to obsession with particular body parts, rather than seeing a body as a whole or focusing on their overall sense of self⁴.
Decision-making: research has demonstrated an increased difficulty for individuals with AN to make decisions compared with healthy controls. Additionally, individuals with AN can delay rewards (e.g. food) to gain long-term rewards (e.g. weight loss)⁸.

Current drawbacks of cognitive impairment research in eating disorders:

A large focus has been placed on central coherence and set shifting in AN, whereas other eating disorders and cognitive difficulties remain under-researched⁹.
All eating disorders commonly experience co-morbidities, both with other eating disorders and with other psychiatric conditions, which themselves may cause cognitive impairments which will need to be accounted for⁴.
Methodologies, cognitive tasks, and sample sizes vary, and the environments tend to be limited. Consistency in methods, tests, and diverse environments is required to catch a range of eating disorders.

By understanding the cognitive impairments in different patient groups, diagnoses, illness duration, and other factors, we will be able to further understand the impact eating disorders have on cognition and how treatment modalities can be implemented to support the person’s recovery.

How CANTAB^® has been used in eating disorder research

Reflecting public consciousness of eating disorders, the majority of CANTAB^® research into eating disorders has been conducted in Anorexia Nervosa (AN), with some research investigating Bulimia Nervosa (BN), as well as Binge Eating Disorder (BED) and Food Addiction (FA).

In BED Research, the Rapid Visual Information Processing (RVP), Intra-Extra Dimensional Set Shift (IED) and Cambridge Gambling Task (CGT) CANTAB tasks were used to determine that obese people with and without BED can be distinguished by scores of attention, reversal learning and risk-taking and decision making. Furthermore, the obese group could be distinguished from normal-weight controls by scores of impulse control in decision-making¹⁰. These results demonstrate that BED has unique cognitive factors associated with it that are separable from those associated with obesity: whilst many people with BED are obese, and many people who are obese have BED, the cognitive picture associated with obesity and how it develops may be more complex than many imagine.

A further link between scores of attention and binge eating was demonstrated in a study of adolescents with a high level of food addiction. Adolescents with high food addiction scores showed impaired performance on the RVP task, alongside significantly higher self-reported measures of executive functioning, impulsivity, depression, and binge eating. These results suggest that cognitive difficulties in food addiction are related to binge eating and psychological symptoms¹¹.

CANTAB has been used to identify impairments in psychomotor speed in AN¹², and to demonstrate that recovery from AN may improve cognitive function: a longitudinal study found that a year after hospitalisation, psychomotor speed in children and adolescents with AN improved to the point of normalisation with controls¹³.

CANTAB has also been used to investigate executive functioning in AN. The Stop Signal Reaction Task (SST) was used to demonstrate that women with AN had significantly impaired motor inhibition when compared with healthy controls¹⁴. This impairment was greater in those with a binge-purge subtype, in line with evidence that impairments in motor inhibition are observed in BN. Furthermore, it was discovered that those in the AN group with impaired motor inhibition made significantly more errors in the Extra-Dimensional shift element of the Intra-Extra Dimensional Set Shift task (IED) than those without. This demonstrates that some cognitive domains may be linked in AN and poses the question of whether impairment in one domain causes impairment in another, or if impairment in both is caused by a common factor. The IED task was also used in a study examining olfactory sensitivity in AN: it was discovered that patients with AN exhibited poor cognitive flexibility compared to healthy controls¹⁵. This study also investigated odour sensitivity in line with the hypothesis that reduced olfactory capacity may reduce the appeal of food and make restricting food intake easier; it is interesting to note that the reduced cognitive flexibility seen in the AN group correlated with olfactory capacity, which was itself significantly poorer in the AN group than in controls.

Conclusion

The study of cognition in eating disorders is a developing field, with many questions left unanswered. The nature of eating disorders themselves make study of their associated impairments complex, as many people living with eating disorders are affected by more than one, as well as other mental health conditions like depression. Nevertheless, existing research, including that carried out using CANTAB, has begun to discover trends in cognitive impairments in eating disorders. Up to this point, Anorexia Nervosa has dominated research, including in the CANTAB literature, despite it being the least common eating disorder. As public consciousness changes about the prevalence of different eating disorders, this may change in the future. Research has focused on executive function, particularly in set-shifting. CANTAB has been shown to be sensitive to set-shifting in AN, as well as other executive function domains and psychomotor speed, as well as sensitive to impairments in BED relating to attention and executive function. As awareness around eating disorders grows, the amount of research into cognition in this area looks set to increase.

References

1: BEAT Eating disorders, 2023
2: American Psychological Association, 2023
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4: Smith, K. E., Mason, T. B., Johnson, J. S., Lavender, J. M., & Wonderlich, S. A. (2018). A systematic review of reviews of neurocognitive functioning in eating disorders: The state‐of‐the‐literature and future directions. International Journal of Eating Disorders, 51(8), 798-821.
5: Monica, D., Paulo, M., Appolinário, J. C., Freitas, S. R. D., Coutinho, G., Santos, C., & Coutinho, W. (2010). Assessment of executive functions in obese individuals with binge eating disorder. Brazilian Journal of Psychiatry, 32, 381-388.
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15: Karavia, A., Kapsali, F., Gonidakis, F., Koliou, A., Tsigkaropoulou, E., Papageorgiou, C., & Michopoulos, I. (2022). Olfactory capacity in anorexia nervosa: correlations with set-shifting ability. Eating and Weight Disorders-Studies on Anorexia, Bulimia and Obesity, 1-8.