Cognitive impairment in mania

In contrast to the large amount of work devoted to the cognitive changes accompanying depression, only a few studies have addressed the precise nature of impairment in patients with mania. A possible explanation for this imbalance may be the practical difficulties of using standard neuropsychological procedures to assess mania; the nature of the illness may prevent patients with mania from being reliable subjects, especially in tests of cognitive functioning. Nevertheless, it has long been recognised that mania is associated with changes in cognition as well as in affect (Kraepelin, 1921; Bunney & Hartmann, 1965), and more recent empirical studies confirm this view.

Patients with mania have been studied using tasks that sample aspects of learning and memory, visuospatial ability and executive function. In a study conducted by Taylor & Abrams (1986), tests of attention, visuospatial function and memory were administered to patients with mania, approximately half of whom exhibited moderate or severe global cognitive impairment. With respect to memory processes, Bunney & Hartmann (1965) noted memory loss during manic states in a patient with regular manic-depressive cycles every 48 hours. Furthermore, Henry et al (1971) reported impaired serial word list learning during mania, with decrements in performance directly related to increasing severity of illness. More recent findings suggest that patients with bipolar disorder in the manic phase of their illness are impaired on tests of pattern and spatial recognition memory and delayed visual recognition (Murphy et al, 1999). In an attempt to explain observed memory deficits, Henry et al (1971) proposed that memory impairment may at least sometimes be owing to altered patterns of verbal association. Andreasen & Powers (1974) reached a similar conclusion with their finding that, relative to control subjects, the memory structures of patients with mania were loose, overinclusive and idiosyncratic, leading to difficulties in filtering environmental stimuli and a tendency to overgeneralise.

The notion that mania is associated with some form of ‘dysexecutive syndrome’ also seems reasonable, since patients typically exhibit disrupted social behaviour and decision-making reminiscent of that observed in patients with lesions to frontal regions of the cortex (Bechara et al, 1994). It is thus surprising that so little research assesses executive functioning in these patients. To date, this type of functioning has been studied using tests of attentional set-shifting (Morice, 1990; Clark et al, 2000), planning ability (Murphy et al, 1999) and decision-making (Clark et al, 2000; Murphy et al, 2001). Although impairments have been observed across the full range of tasks, it is not yet clear to what extent these deficits stand over and above those observed in other non-executive domains.