Progress in Neuro-Psychopharmacology and Biological Psychiatry
Sustained attention deficits in manic and euthymic patients with bipolar disorder
Introduction
Neurocognitive dysfunction in the discrete phases of bipolar disorder (BPD) is increasingly being reported. Besides manic and depressive episodes, cognitive deficits are also reported to persist in remitted patients with bipolar disorder. Executive function, verbal memory and sustained attention deficits are among the most commonly reported impairments in bipolar disorder (Glahn et al., 2004, Quarishi and Frangou, 2002, Savitz et al., 2005, Thompson et al., 2005). Studying the neurocognitive dysfunction in bipolar disorder can provide a potential link from the neuropsychological symptoms of the disorder to the underlying neurobiological mechanisms.
Continuous performance tests (CPT) are used to assess sustained attention and vigilance. Several studies reported decreased target sensitivity (omission errors) in various CPT tasks in euthymic patients with bipolar disorder (Bora et al., 2005, Clark et al., 2002, Clark and Goodwin, 2004, Liu et al., 2002, Swann et al., 2003) although some other studies did not replicate these results (Bozikas et al., 2005, Robertson et al., 2003). Bozikas et al. reported sustained attention deficits in patients with schizophrenia but not in euthymic patients with bipolar disorder. There is also some evidence for decreased target sensitivity and increased false responding in acute mania (Clark et al., 2001, Clark and Goodwin, 2004, Liu et al., 2002, Sax et al., 1998). The samples in these studies were small. In these studies, several different versions of CPT; RVIP (Rapid Visual Information Processing task) (Clark et al., 2001), degraded-stimulus CPT (Liu et al., 2002) and IMT–DMT (Immediate Memory Test–Delayed Memory Test) (Swann et al., 2003) were used. In several of these studies, the CPT performances of euthymic and manic bipolar patients were also compared (Fleck et al., 2005, Liu et al., 2002, Swann et al., 2003). Increased false responding was prominent only in the manic state. These studies failed to find a correlation between target sensitivity and the severity of mania, however, their sample sizes were small.
Some authors propose that the decreased target sensitivity may be a vulnerability indicator of bipolar disorder. This impairment may be exacerbated in the manic state and is accompanied by an increased rate of false responding (Clark and Goodwin, 2004). This cognitive profile suggests a trait-related impairment which is modulated by state. In this study, the sustained attention deficits were found to be unrelated to the dose and the type of the medications.
One of the objectives of the study was to compare the performances of euthymic and manic bipolar patients on three dimensions of sustained attention and to try to differentiate impairments of euthymic patients from state dependent deficits. Our first hypothesis was that decreased target detection and reaction time (RT) inconsistency would be present even in euthymic patients and we suggested that these impairment would be exacerbated during mania. In addition to these impairments, we expected that manic patients would also have attention impairments in impulsivity and vigilance dimensions of the task. Originally, the performances of manic patients on some new attentional measures like perseveration and reaction time inconsistency were investigated.
Another objective was to investigate the relationship between the attention deficits in manic state and medication effects. Clark and Goodwin investigated the association of attention deficits with the type and dose of the medications. As an original contribution of this study, we also used the sedation scores of the manic patients as an indirect indicator of the impact of pharmacological treatment on attention. We hypothesized that exacerbation of trait-related impairments in mania could be explainable, at least partly, by the impact of treatment.
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Participants
Before the administration of the sustained attention task, all of the manic patients were assessed with Young Mania Rating Score (YMRS) and sedation item of the UKU (Udvalg ter Kliniske Undersogelser) scale (Lingdaerde et al., 1987). The euthymic patients were assessed by Hamilton Depression Rating Scale (HDRS) (Akdemir et al., 2001, Hamilton, 1960) and YMRS ( Karadag et al., 2002, Young et al., 1978). Clinical variables were collected by psychiatric interview and by review of the Affective
Clinical and demographic variables
The demographic and clinical characteristics of the three groups are summarized in Table 1. Although mean age of the manic patients were a little younger than euthymic bipolar and control groups, this difference was not statistically significant. The duration of illness was significantly longer in euthymic patients. The mean duration of remission of the euthymic patients was 52.3 (S.D. = 59.3) months.
Sustained attention variables
MANOVA analysis revealed a highly significant between group difference (Pillai = 4.26, p < 0.001).
Discussion
This study compares the manic and euthymic patients with bipolar disorder with healthy subjects on various components of sustained attention. The manic patients had a more severe and a different pattern of sustained attention deficits compared to euthymic patients. Both of our first two hypotheses about the relationship between mania and attention deficits were supported.
The euthymic patients with bipolar disorder were impaired on the three measures of the sustained attention task. All of these
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