Delusions (DD) are a form of psychosis that have been shown to be both similar and different from other psychotic conditions. Some research has shown that people with DD have impaired cognitive abilities, while other research has provided evidence of fully intact working memory, reasoning, and cognitive functions. In fact, one of the markers that is used to distinguish DD from schizophrenia is normal cognitive capacity.
Another difference between the two conditions is that delusions in DD are not bizarre and unusual like those of schizophrenia, but rather, the delusions in DD are grandiose and elaborate and require a highly functional neurocognitive architecture for their development. Because the existing research on DD has provided mixed results with respect to executive function impairment, Inmaculada Ibanez-Casas of the Institute of Neuroscience at the University of Granada in Spain chose to focus on cognitive function in DD for a recent study.
Using a sample of 86 participants with DD and 343 non-DD controls, Ibanez-Casas conducted a battery of memory, reasoning, and cognitive tests. The results revealed that although there were some similarities in performance, perhaps as a result of hypervigilance in the DD sample, the overall performance of the DD participants was worse than the performance of the controls. Deficits were found in areas of reasoning, memory, flexibility, executive function updating and impulse control. When Ibanez-Cases controlled for age, gender, and IQ, the results persisted.
The results of this study clearly show an impaired cognitive capacity in individuals with DD, which is in direct contrast to some existing research. Despite the fact that cognitive preservation has been evidenced in other studies, Ibanez-Casas’ study demonstrates a significant deficit in core areas of cognitive functioning. Additionally, other research has suggested that people with DD not only have fully intact cognitive abilities, but these abilities show no sign of devolving over time as is the case with other psychotic conditions, such as schizophrenia.
“On the contrary,” added Ibanez-Casas, “If compared with previous studies on schizophrenia, executive function in DD could be postulated as being halfway between that of patients with schizophrenia and controls.” Clearly, despite the large sample used in this study and the exhaustive tests conducted on the participants, further research must be conducted to support the findings provided here.
Ibanez-Casas, I., De Portugal, E., Gonzalez, N., McKenney, K.A., Haro, J.M., et al. (2013). Deficits in executive and memory processes in delusional disorder: A case-control study. PLoS ONE 8(7): e67341. doi:10.1371/journal.pone.0067341
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