Article summary of The association between executive functioning and psychopathology: general or specific? by Bloemen a.o. - 2018

Background: we modeled both psychopathology and executive function (EF) as bi-factor models to study if EF impairments are transdiagnostic or relate to individual syndromes, and if such associations are with general or specific EF impairments.

Introduction

Problem domains of psychopathology are highly correlated, both concurrently and over time. Its proposed that the structure of psychopathology is best captured by a bi-factor model of general psychopathology on one side and specific problem domains on the other. Specific problem domains include internalizing (INT), externalizing (EXT), as well as ADHD and autism spectrum disorder (ASD) problem domains. The bi-factor model separates what is common across different psychopathology domains from what is unique for each domain.

EF is crucial for our daily functioning in guiding goal-directed behaviour. It includes a broad range of cognitive processes, e.g. suppressing automatic responses, switching between tasks, maintaining/updating information etc. Different theoretical models of EF share the idea that the structure of EF includes general and specific parts. EF’s have something in common, but are separable from one another.

EF impairments are widely accepted as a common characteristic of various psychiatric disorders. The focus has long been on finding distinct cognitive profiles for these disorders, which has produced inconsistent findings. Research hasn’t converged on which EFs are impaired in each disorder. Has been found that EF dysfunctions are generally widespread, severe, and pronounced in disorders that are severe and chronic e.g. schizophrenia. Conversely, no findings have been reported in younger populations with mild to moderately severe disorders like depression or anxiety. Caspi et al. (2013) has shown that poorer performance on EF tasks was associated with the general psychopathology factor (p factor) but not with specific INT and EXT factors.  Furthermore, EF seems more impaired when multiple conditions are present. together, findings suggest that EF impairments are more strongly associated with severity and chronicity of psychiatric problems than with distinct diagnoses – could explain discrepancies in research where focus has been on distinct disorders.

One could ask whether impairments in general or specific EF are related to psychopathology. Studies have previously only examined either EF performance on lumped or on separate neuropsychological tasks.  Studies using separate tasks have shown uniform impairments across tasks relating to psychopathology – may indicate that EF is not process specific when associated with psychopathology. This is also suggested by other studies that have lumped scores on EF tasks. Although these findings suggest an association at the general EF level, aggregation through sum or factor scores still captures the scores on individual tasks. Given this overlap, no firm conclusions can be made. In contrast, a bi-factor model splits the variance into general and specific parts. So bi-factor models allow for a clear-cut interpretation of the extent to which associations between psychopathology and EF can be summarized as generic or more separable.

To summarize, it’s generally agreed on that multiple EF impairments are involved in a range of disorders. But extensive research hasn’t agreed on distinct EF profiles for distinct disorders. This study investigates whether EF problems relate to severity/chronicity of psychopathology rather than type. It’s addressed whether general or specific EF impairments associate with psychopathology. This will be done by modeling psychopathology as measured over multiple occasions during the course of adolescence in a bi-factor model. Also, EF will be modeled as measured at two occasions during adolescence in a bi-factor model. Through this bi-factor approach, the study aims to understand the relationship between psychopathology and EF. Hypothesis: association is generic. EF impairments only associated with general psychopathology.

Method

Sample

2230 adolescents from the Tracking Adolescents’ Individual Lives Survey.

Measures

• Child Behaviour Checklist: parent rated questionnaire.
• Child Social Behaviour Questionnaire: captures six symptom dimensions typically seen in children with ASD.
• Executive functioning: using 1) Baseline Speed Task, 2) Feature Identification Task, 3) Sustained Attentional Dots Task, 4) Memory Search Letters Task, 5) Shifting Attentional Set Task

Discussion

Study modeled both psychopathology and EF as bi-factor models to examine whether EF impairments are transdiagnostic or relate to individual syndromes – and if these associations are with general or specific EF impairments. With the double bi-factor approach, the best model showed that impairments in multiple specific EFs are associated with general psychopathology. Especially true for ADHD and ASD problems. Furthermore, INT problems have a distinct association with cognitive flexibility. We can draw stronger conclusions with regard to findings from the ‘psychopathology side’ than the ‘EF side’ of the double bi-factor model. So we conclude that inconsistent findings in literature may be due to substantial transdiagnostic EF impairments. Also once these transdiagnostic impairments are captured, ADHD, ASD, and INT problems still have their specific EF profile. Thirdly, whether general or specific EF relates to the p-factor needs to be studied more.

Caspi et al. research was extended by including ADHD and ASD problems. IN line with their findings, this study showed associations with the p factor. The p factor captures all the shared variance between different problem domains and is often considered to reflect severity and chronicity of psychopathology.

INT and EXT problems alone don’t show much impairment in EF beyond severity and chronicity captured by the p factor. Caspi et al. found no associations between cognitive flexibility and INT problem domain like this study, but this could be due to cognitive flexibility being measured with different tasks. Results suggest that cognitive inflexibility may be a core cognitive deficit of INT problems. Makes sense when thinking about the connection between cognitive flexibility and rumination – key component of INT disorders. People with impaired cognitive flexibility less able to ‘reset’ their minds after daily hassles and therefore fixate on their thoughts evoking feelings of worry.

The ASD and ADHD problem domains show associations with specific EFs above and beyond associations with severity and chronicity of psychopathology. Both show impairments in visuospatial working memory, sustained attention, feedback responsiveness, and cognitive flexibility – impairments in psychomotor speed and working memory maintenance were specific to ADHD. Although the adolescent sample represents absent-to-very mild severity in ASD, study demonstrates that EF impairments are present. moreover, although ASD often is considered a more severe neurodevelopmental disorder than ADHD, this study found that EF impairments are somewhat more widespread/stronger in ADHD.

One of the biggest strengths of this study is the use of neuropsychological data in an epidemiological context – making for fairly unique data. Moreover, the study included ADHD and AS, lifespan conditions not be ignored as specific problem domains when trying to understand the structure of psychopathology. Finally, EF was modeled with a bi-factor model. By partialling out shared variance between EF tasks, measurement error and state-specific variance were minimized. Specific EFs may in part still measure non-EF-related variance as the study was unable to use multiple tasks for each specific cognitive process. Nonetheless, the task impurity problem was tackled to some extent.

This study had several limitations:

1. Consider the dropout rate of the sample – may not be fully representative of the general population.
2. Had a limited set of EF measures that assess fairly specific EF dimensions, rather than more complex processes or higher order EFs which are more closely related to behaviour.
3. Use of EF measures differs greatly between studies. Emphasizes need for future studies to determine if these conclusions hold in samples using different tasks.
4. Though there isn’t literal overlap in items and constructs, the items do tend not to be fully specific for the construct they measure – limiting the specificity of the psychopathology domains.
5. Use of parent-reported questionnaires may have different properties for INT and EXT issues.

By studying diverse psychopathology domains simultaneously, this study showed that EF problems cross diagnostic boundaries and play a domain-specific role in ADHD, ASD, and INT symptomatology. It’s concluded that the association between psychopathology and EF can’t simply be considered either generic or specific and examining both components of EF and psychopathology allows for clearer conclusions on distinct EF profiles for distinct disorders.