A unifying theory for cognitive abnormalities in functional neurological disorders, fibromyalgia and chronic fatigue syndrome: systematic review

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Abstract

Background Functional cognitive disorder (FCD) describes cognitive dysfunction in the absence of an organic cause. It is increasingly prevalent in healthcare settings yet its key neuropsychological features have not been reported in large patient cohorts. We hypothesised that cognitive profiles in fibromyalgia (FM), chronic fatigue syndrome (CFS) and functional neurological disorders (FNDs) would provide a template for characterising FCD. Methods We conducted a systematic review of studies with cognition-related outcomes in FM, CFS and FND. Results We selected 52 studies on FM, 95 on CFS and 39 on FND. We found a general discordance between high rates of subjective cognitive symptoms, including forgetfulness, distractibility and word-finding difficulties, and inconsistent objective neuropsychological deficits. Objective deficits were reported, including poor selective and divided attention, slow information processing and vulnerability to distraction. In some studies, cognitive performance was inversely correlated with pain, exertion and fatigue. Performance validity testing demonstrated poor effort in only a minority of subjects, and patients with CFS showed a heightened perception of effort. Discussion The cognitive profiles of FM, CFS and non-cognitive FND are similar to the proposed features of FCD, suggesting common mechanistic underpinnings. Similar findings have been reported in patients with mild traumatic brain injury and whiplash. We hypothesise that pain, fatigue and excessive interoceptive monitoring produce a decrease in externally directed attention. This increases susceptibility to distraction and slows information processing, interfering with cognitive function, in particular multitasking. Routine cognitive processes are experienced as unduly effortful. This may reflect a switch from an automatic to a less efficient controlled or explicit cognitive mode, a mechanism that has also been proposed for impaired motor control in FND. These experiences might then be overinterpreted due to memory perfectionism and heightened self-monitoring of cognitive performance.

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Toward a Rational and Mechanistic Account of Mental Effort

Matthew Botvinick, Jonathan D. Cohen, Thomas L Griffiths … (2017)

In spite of its familiar phenomenology, the mechanistic basis for mental effort remains poorly understood. Although most researchers agree that mental effort is aversive and stems from limitations in our capacity to exercise cognitive control, it is unclear what gives rise to those limitations and why they result in an experience of control as costly. The presence of these control costs also raises further questions regarding how best to allocate mental effort to minimize those costs and maximize the attendant benefits. This review explores recent advances in computational modeling and empirical research aimed at addressing these questions at the level of psychological process and neural mechanism, examining both the limitations to mental effort exertion and how we manage those limited cognitive resources. We conclude by identifying remaining challenges for theoretical accounts of mental effort as well as possible applications of the available findings to understanding the causes of and potential solutions for apparent failures to exert the mental effort required of us.

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Cognitive function in fibromyalgia patients.

L Crofford, Elizabeth Glass, Michelle D. Park … (2001)

To evaluate fibromyalgia (FM) patients for the presence of cognitive deficits and to test the hypothesis that abnormalities would fit a model of cognitive aging. We studied 3 groups of patients: FM patients without concomitant depression and in the absence of medications known to affect cognitive function (n = 23), age- and education-matched controls (n = 23), and education-matched older controls who were individually matched to be 20 years older (+/- 3 years) than the FM patients (n = 22). We measured speed of information processing, working memory function, free recall, recognition memory, verbal fluency, and vocabulary. We correlated performance on cognitive tasks with FM symptoms, including depression, anxiety, pain, and fatigue. We also determined if memory complaints were correlated with cognitive performance. As expected, older controls performed more poorly than younger controls on speed of processing, working memory, free recall, and verbal fluency. FM patients performed more poorly than age-matched controls on all measures, with the exception of processing speed. FM patients performed much like older controls, except that they showed better speed of processing and poorer vocabulary. Impaired cognitive performance in FM patients correlated with pain complaints, but not with depressive or anxiety symptoms. FM patients reported more memory problems than did the older and younger controls, and these complaints correlated with poor cognitive performance. Cognitive impairment in FM patients, particularly memory and vocabulary deficits, are documented in the study. Nevertheless, the intact performance on measures of information processing speed suggests that the cognitive deficits are not global. FM patients' complaints about their memory are likely to be legitimate, since their memory function is not age appropriate.

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Identifying the clinical domains of fibromyalgia: contributions from clinician and patient Delphi exercises.

Roderick Williams, P J Mease, Leslie Crofford … (2008)

In evaluating the effectiveness of fibromyalgia (FM) therapies, it is important to assess the impact of those therapies on the full array of domains considered important by both clinicians and patients. The objective of this research was to identify and prioritize the key clinically relevant and important domains impacted by FM that should be evaluated by outcome assessment instruments used in FM clinical trials, and to approach consensus among clinicians and patients on the priority of those domains to be assessed in clinical care and research. Group consensus was achieved using the Delphi method, a structured process of consensus building via questionnaires together with systematic and controlled opinion feedback. The Delphi exercises involved 23 clinicians with expertise in FM and 100 patients with FM as defined by American College of Rheumatology criteria. The Delphi exercise revealed that the domains ranked most highly by patients were similar to the domain rankings by clinicians. Pain was consistently ranked highest by both panels. Fatigue, impact on sleep, health-related quality of life, comorbid depression, and cognitive difficulty were also ranked highly. Stiffness was ranked highly by patients but not clinicians. In contrast, side effects was important to clinicians but was not identified as important in the patient Delphi exercise. The clinician and patient Delphi exercises identified and ranked key domains that need to be assessed in FM research. Based on these results, a conceptual framework for measuring patient-reported outcomes is proposed.