This website is written by Taylor Bak. Many studies have supported that depression causes cognitive impairment (Beats, Sahakian & Levy, 1996; Porter, Bourke & Gallagher, 2007). These impairments include deficits in short-term memory, verbal and visual recognition memory, spatial recognition memory, and both immediate and delayed memory recall (Murphy, & Sahakian, 2001) Clinically depressed patients perform worse on tests of executive function, including the Wisconsin Card Sorting Task (WCST) and the Tower of London test of planning ability. These tests both assess the functioning of the prefrontal cortex, an area crucial for decision making. Research has shown significant differences between people with bipolar depression and unipolar depression. Bipolar patients receive lower scores on tests of learning and verbal fluency (Wolfe, Granholm, Butters, Saunders, & Janowsky, 1987). Although it is generally recognized that mania causes functional cognitive impairments, few studies have addressed it. It is difficult to give neuropsychological tests to patients who are acutely manic. One study administered tests of attention, visuospatial function and memory to manic patients and found that half exhibited moderate to severe cognitive impairment (Taylor & Abrams, 1986). Manic patients display impaired serial list learning, and patients who have more severe mania have a worse deficit (Henry, Weingartner & Murphy, 1971). Serial list learning requires subjects to learn a list of words in order and repeat them. The authors refer to this as a “reversible learning disorder” that occurs only during mania. Additionally, manic patients are impaired on tests of pattern and spatial recognition memory and delayed visual recognition. People with bipolar disorder, like those with depression, have diminished executive functioning skills due to reduced activity in the prefrontal cortex. Bipolar patients exhibit this dysfunction even while in the euthymic, or non-manic and non-depressive state of remission, although to a lesser degree. Many neuropsychological studies have been conducted to distinguish mania from psychosis induced by schizophrenia, since the two are often confused. Manic and schizophrenic people tend to do similarly on tests of selective attention, perceptual span (which measures the region of effective vision during eye fixations while reading), and shifting attention set, which is a measure of cognitive flexibility, the ability to think about two concepts at once or shift between mental concepts smoothly. Andreasen & Powers (1974) found that overinclusive thinking, the inability to confine thoughts within the boundaries of one given topic, is more common in manic episodes than in schizophrenic episodes. Patients with schizophrenia perform more poorly than patients with bipolar disorder on tests of psychomotor speed, attention, and memory. Additionally, within-subject studies have been conducted to determine the neuropsychological differences between mania and depression. Bulbena & Berrios (1993) utilized a neuropsychological battery of tests of attention, memory, visuospatial functioning and choice reaction time. Patients performed worse than controls, but at the same level during manic and depressive states. Another study found no significant differences in intelligence (measured by the Wechsler Adult Intelligence Scale) or in tests of reading, line orientation and facial recognition (Goldberg et al., 1993). Patients in a manic state differ from patients in depressive states in that their pattern and spatial recognition memory are more impaired.
Andreasen, N. J. C., & Powers, P. S. (1974). Overinclusive thinking in mania and schizophrenia. The British Journal of Psychiatry, 125(588), 452-456.
Beats, B. C., Sahakian, B. J., & Levy, R. (1996). Cognitive performance in tests sensitive to frontal lobe dysfunction in the elderly depressed. Psychological medicine, 26(3), 591-603.
Bulbena, A., & Berrios, G. E. (1993). Cognitive function in the affective disorders: a prospective study. Psychopathology, 26(1), 6-12.
Goldberg, T. E., Gold, J. M., Greenberg, R., Griffin, S., Schulz, S. C., Pickar, D., … & Weinberger, D. R. (1993). Contrasts between patients with affective disorders and patients with schizophrenia on a neuropsychological test battery. The American Journal of Psychiatry.
Henry, G. M., Weingartner, H., & Murphy, D. L. (1971). Idiosyncratic patterns of learning and word association during mania. American Journal of Psychiatry, 128(5), 564-574.
Porter, R. J., Bourke, C., & Gallagher, P. (2007). Neuropsychological impairment in major depression: its nature, origin and clinical significance. Australian & New Zealand Journal of Psychiatry, 41(2), 115-128.
Murphy, F. C., & Sahakian, B. J. (2001). Neuropsychology of bipolar disorder. The British Journal of Psychiatry, 178(S41), s120-s127.
Taylor, M. A., & Abrams, R. (1986) Cognitive dysfunction in mania. Comprehensive Psychiatry. 27. 186-191.
Wolfe, J., Granholm, E., Butters, N., Saunders, E., & Janowsky, D. (1987). Verbal memory deficits associated with major affective disorders: a comparison of unipolar and bipolar patients. Journal of Affective Disorders, 13(1), 83-92.
The Biological Underpinnings of Bipolar Disorder 