Synthesis of the existing literature about cognitive function in women with anorexia nervosa and bulimia nervosa. MSc dissertation, part 1.
This systematic review aimed to synthesize the existing literature about cognitive functioning and eating disorders, and attempted to answer the question: is there evidence of a different cognitive performance in women with eating disorders? The full text is available for interested readers.
Search strategy
The following electronic databases were searched on the 25th of January 2019: EBSCOhost, including PsycINFO, and Web of Science, including MEDLINE and SciELO Citation Index. A search strategy was developed, and adapted for each electronic database. Search outputs were managed using EndNote software. Electronic databases outputs reached 505 articles after duplicate removal. Titles and/or abstracts were screened with reference to an eligibility checklist. This process excluded 453 articles. Full text was obtained for all 52 potentially relevant papers that remained. These were assessed by the eligibility checklist, and reasons for exclusion were documented. This process excluded 30 articles. In the end, the systematic review included 22 articles. The quality of the articles was assessed using the Checklist for Analytical Cross Sectional Studies, designed by The Joanna Briggs Institute.
Executive Functions
Set-shifting
In general, AN showed difficulties in set-shifting tasks compared with HC; though, results showed a high variability depending on the age, the stage of the illness, and the test used.
When samples were stratified by age, two studies found negative small and medium effect sizes in adolescents (TMT: d=.32; WCST: d=.56) and in adults (TMT: d=.20; WCST: d=.40), whereas other studies reported a normal performance of AN adolescents.
The stage of the disease seemed to also influence in set shifting abilities. One study reported that acute AN presented more difficulties than in treatment and recovered AN. Other authors reported that acute first episode and recovered AN had difficulties with small-medium effect sizes (r=.22) compared with HC; although, acute first episode AN were the most impaired of the clinical sample, with medium effect sizes (ds=.51 to .58). In contrast, only one paper found non-significant differences between acute AN and HC.
Central coherence
AN participants showed weak central coherence compared with HC, with small to medium effect sizes (rs=.17 to .34, d=.23). Difficulties were found in adolescents and adults, during acute and recovered phases of the disease; though, they seemed to positively correlate with the severity of the symptoms.
Decision-Making
AN participants showed difficulties in tasks assessing decision-making abilities, where they took more disadvantageous, risky, impulsive choices, and failed to learn from the feedback. More in detail, AN adolescents showed negative small effects (d=.28), while adults showed small-medium negative effects (d=.47), with no significant differences between acute and recovered patients.
Working memory
AN adolescents showed difficulties in working memory tasks, with small effect sizes (d=.26), however, adults did not display differences compared to HC. Patients in acute and recovered phases showed deficits compared with HC, with small-medium effects (r=.22); though, acute patients showed higher impairments compared with recovered patients, with medium effect sizes (d=.50).
Verbal Fluency
One study did not find significant differences between adolescents and adults with acute AN and HC, either in semantic or phonemic verbal fluency. Although, another study found that AN adolescents presented difficulties in both semantic (p<.012) and phonemic (p<.04) verbal fluency tasks. Thus, age seemed to correlate negatively with their performance, with adolescents being the most impaired of the samples.
Planning
One study used the D-KEFS Tower Test to assess planning ability in children and adolescents with AN, and it found that the total number of moves and the total number of errors lay within the normal range and did not differ from HC; although, AN were faster in their first move, and better on orientation and strategy-learning, with small-medium and medium-large effects.
Social domain
Social cognition was widely studied. It was found that recovered AN showed more deficits (d=.8) compared with acute first episode AN. More in detail, recovered AN showed difficulties in interpreting vocal prosody, with medium effect sizes (d=.6), and difficulties in interpreting body gestures, with large effect sizes (ds=.8 to .9). These results suggested that the duration of the illness positively correlated with social cognition performance.
Some studies examined specifically ToM, and found that acute AN and HC had significant differences: p=.025 and p<.018, with the AN group being more impaired, with small-medium effect sizes (d=.40). Only one study found no significant differences between AN and HC.
Other studies examined specifically AR, and found that acute AN and HC had significant differences: p=.049, with the AN group being more impaired, with medium effect sizes (d=.64). Acute AN and BN participants had similar performances in identifying disgust and anger, and both showed deficits compared with HC, with medium effect sizes (disgust AN r=.39, disgust BN r=.34, anger AN r=.36, anger BN r=.32), and medium-large effect sizes when analysed the recognition of both emotions as an ED unitary group (d=.7).
Attention
Assessment of attention has not constituted a frequent research topic in patients with ED. One study showed no significant difference in sustained attention tasks between acute first episode AN, recovered AN and HC. Meanwhile, four studies explored visual selective attention, but results are incongruent. The four samples included adolescent and adult acute AN patients; however, when compared with HC, two studies found no significant differences in their performances, and the other two found a poorer performance of the AN sample (p<.05, p=.002).
Processing speed
Results in processing speed tasks are mostly consistent across studies. No significant difference was found between HC and acute first episode and recovered AN adolescents and adults in three studies. Although, one study reported significant differences between acute AN and HC (p=.002), with the AN group showing impairments, with medium effect sizes (d=.52).
Memory
Visual immediate and delayed recall performance in acute AN adolescents showed no significant difference with HC. However, a sample of adults with AN showed impairment, with medium effect sizes (r=.39) for immediate recall, and medium-large effects for delayed recall (r=.43). Two studies examined verbal memory and found that acute first episode and recovered AN participants had a poorer performance in immediate and delayed recall tasks compared with HC (p<.001), with small-medium effect sizes (r=.2).
Conclusion
This systematic literature review offered evidence that women with ED have a different cognitive performance. Results varied across the studies; nevertheless, in broad terms, a strong correlation between ED and difficulties in executive functions and social cognition was found, especially in set-shifting, central coherence, decision-making, working memory, AR and ToM. While assessment of attention, processing speed, memory, and verbal fluency offered heterogeneous results, language, orientation, planning, impulsivity, and abstraction were consistently preserved across the samples. Surprisingly, AN and BN presented similar cognitive profiles, with hardly any remarkable differences between them.
References
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Giannunzio, V., Degortes, D., Tenconi, E., Collantoni, E., Solmi, M., Santonastaso, P., & Favaro, A. (2018). Decision-making impairment in anorexia nervosa: New insights into the role of age and decision-making style. European eating disorders review : the journal of the Eating Disorders Association, 26(4), 302-314. doi:10.1002/erv.2595
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