Cognitive Impairment in Patients With Bipolar Disorder

It is widely accepted that patients with schizophrenia have some degree of cognitive deficiency and that cognitive deficits are an inherent part of the disorder. Historically, there has been less focus on cognitive deficits in patients with bipolar disorder; however, numerous studies of cognition in patients with bipolar disorder, including several comprehensive meta-analyses of bipolar patients who were euthymic at the time of testing, have recently been undertaken.^1-4 Each of these analyses found that cognitive impairment persists during periods of remission, mainly in domains that include attention and processing speed, memory, and executive functioning.⁴

Cognitive deficit testing

The Brief Assessment of Cognition in Affective Disorders (BAC-A) is composed of 6 subtests of the Brief Assessment of Cognition (BAC) and Brief Assessment of Cognition in Schizophrenia (BAC-S) and 2 additional tests: affective interference and emotion inhibition. The BAC-A takes approximately 45 minutes to administer and is devised for easy administration and scoring. It is specifically designed to measure treatment-related improvements, and it includes 2 alternative forms. A composite score is derived from the 6 subtests of the BAC-A, as well as the BAC and BAC-S. All 3 tests have high test-retest reliability (intraclass correlations > 0.80) in patients and controls, have equivalent forms, and are as sensitive to cognitive dysfunction in schizophrenia as a standard 2.5-hour battery.⁵

The series of tests in the BAC-A includes brief assessments of attention, motor speed, working memory, verbal memory, reasoning and problem solving, verbal fluency, affective interference, and emotion inhibition. All of these tests except emotion inhibition were used by Malhi and colleagues⁶ and are briefly described as follows:

• List learning (verbal memory): Patients are presented with 15 words and then asked to recall as many as possible. This procedure is repeated 5 times. There are 2 alternative forms.

• Digit sequencing task (working memory): Numbers of increasing length are presented orally by the examiner and patients are asked to repeat the numbers from lowest to highest.

• Token motor task (motor speed): Patients are given 100 plastic tokens and asked to place them into a container as quickly as possible for 60 seconds.

• Verbal fluency: Tests of category instances (semantic fluency) and controlled oral word association test (letter fluency) are administered. Patients are given 60 seconds to name as many words as possible within a given semantic category and, in 2 separate trials, patients are given 60 seconds to generate as many words as possible that begin with a given letter. The total number of words from the 3 trials is the outcome measure.

• Tower of London (reasoning and problem solving): Patients look at 2 pictures simultaneously. Each picture shows 3 different-colored balls arranged on 3 pegs, with the balls in a unique arrangement in each picture. The patients are asked to determine the fewest number of times the balls in one picture would have to be moved to make the arrangement of balls identical to that of the opposing picture. There are 2 alternative forms.

• Symbol coding (attention and processing speed): As quickly as possible and for 90 seconds, patients write numerals 1 through 9 as matches to symbols on a response sheet.

• Affective Interference test (emotional distractibility and affective memory): Patients are presented with 20 words: 10 are nonaffective words (fruits and vegetables) and 10 have high emotional valence—either positive (romantic) or negative (cancer). Patients are first given 3 trials to recall all words. They are then cued to recall the nonaffective words and the affective words separately. After a delay, patients are given a recognition trial with the 20 words and 20 foil words. The test requires 5 minutes for a recall trial and 2 minutes for a recognition trial. Because this is an experimental paradigm at this stage, there are 12 different variables; these have been tested to assess the power of discrimination between controls and affective patients.

• Emotion inhibition test: Although not included in the bipolar depression trial described in the depression phase deficits section,5 the BAC-A usually includes an eighth test in which patients are presented with sheets of paper with 4 columns of words (neutral or affective) or symbols in colored or black ink. They are asked to either read the words or name the colors of the ink going down the columns. They get 30 seconds for each page. The key outcome measure is the patient’s ability to name colors of affective words under control conditions.