February 26, 2024

Individuals with bipolar disorder tend to show impairments in multiple cognitive domains

A new study in Canada explored whether cognitive impairments in individuals with bipolar disorder develop early with the onset of the disorder or gradually over time through “accelerated aging.” Results showed that impairments in attention, processing speed and executive function seem to develop gradually. On the other hand, verbal memory impairment seems to develop quickly with the onset of the disorder. The study was published in Psychological Medicine.

Bipolar disorder is a mental health condition characterized by extreme mood swings that include periods of intense mania and periods of deep depression. These mood episodes can vary in intensity and duration. Manic episodes are characterized by elevated mood, increased energy, racing thoughts, and impulsive behavior. During depressive episodes, individuals suffering from bipolar disorder experience profound sadness, loss of interest in activities, fatigue, and difficulty concentrating. These mood shifts can be very disruptive to daily life. Bipolar disorder affects approximately 1-2% of the population.

Recent studies have shown that individuals suffering from bipolar disorder also experience impairments in various cognitive domains compared to healthy individuals. These impairments can be quite severe. They seem to be particularly pronounced during depressive episodes and to improve with the resolution of depressive symptoms. However, they do not disappear completely. Research data indicates that they persist to a certain degree both during manic episodes and during periods when individual’s mood is balanced. These bipolar disorder-related cognitive impairments tend to be more pronounced in older individuals.

Study author Brett D. M. Jones and his colleagues wanted to explore how these cognitive impairments develop. They considered three possibilities: 1. cognitive impairment might start early and persist as individuals age (“early hit” hypothesis), 2. cognitive abilities might decline faster with age in individuals with bipolar disorder, leading to accelerated aging effects (“accelerated aging” hypothesis), or 3. a combination of both factors might be at play.

To investigate these possibilities, they compared the cognitive performance of individuals with bipolar disorder of different ages to healthy individuals. The data for this comparison came from four different studies conducted at the Centre for Addiction and Mental Health in Toronto, Canada.

The participants were divided into four groups: younger individuals (up to 49 years old) with bipolar disorder, older individuals (50 years and above) with bipolar disorder, healthy individuals up to 49 years old, and healthy individuals 50 years and above. They all completed a battery of neuropsychological assessments (the MATRICS Cognitive Consensus Battery) and additional tests to assess seven different cognitive domains: attention/vigilance, information processing speed, executive function/working memory, visuospatial memory, verbal memory, reasoning and problem solving, and social cognition. The researchers estimated participants’ intelligence before the onset of the disorder using the Wechsler Test of Adult Reading.

The results showed that younger participants with bipolar disorder developed the condition at around 19 years old on average, while older participants developed it at around 30 years old on average. Participants experienced around three times more depressive episodes than manic episodes. Before developing bipolar disorder, their intelligence levels were similar to those of healthy participants.

When comparing cognitive performance, participants with bipolar disorder performed worse than healthy individuals of the same age on most cognitive tests. The differences were more pronounced in the older groups.

After analyzing the data, the researchers found that differences in attention, processing speed, and executive function between younger individuals with and without bipolar disorder followed the pattern consistent with the accelerated aging hypothesis. The gap in cognitive performance between these groups increased with age.

On the other hand, differences in verbal memory supported the “early hit” hypothesis, showing that verbal memory impairments developed quickly with the onset of bipolar disorder. There were no significant differences between groups in social cognition. Visual spatial memory and reasoning/problem-solving were worse in older groups, but this was not directly related to bipolar disorder.

“Our study supports the concept of accelerated aging in bipolar disorder for the domains of attention/vigilance, processing speed, and executive function/working memory. It also supports the concept of an early impairment associated with some (unspecified) neurodevelopmental process for verbal memory, and declines due to normal aging for the domains of reasoning/problem solving and visuospatial memory,” the study authors concluded.

The study makes an important contribution to the scientific understanding of cognitive functioning of individuals with bipolar disorder. However, it also has limitations that need to be taken into account. Notably, this was a cross-sectional study, so it remains unknown whether the observed differences are between people of different age or between different generations. Also, study design does not allow any cause-and-effect conclusions to be drawn from the results.

The study, “A cross-sectional study of cognitive performance in bipolar disorder across the lifespan: the cog-BD project”, was authored by Brett D. M. Jones, Brisa S. Fernandes, M. Ishrat Husain, Abigail Ortiz, Tarek K. Rajji, Daniel M. Blumberger, Meryl A. Butters, Ariel G. Gildengers, Tatiana Shablinski, Aristotle Voineskos, and Benoit H. Mulsant.

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