Sustained attention deficit in bipolar disorder is not a working memory impairment in disguise
Introduction
Bipolar disorder is characterised by recurrent episodes of mania and depression, interspersed with periods of apparent recovery. However, recovery is often not complete, there remains a high incidence of occupational, psychological and social difficulties during remission [6], [11], [23]. Perhaps consistent with these observations, independent neuroimaging investigations have reported stable structural abnormalities and MRI signal hyperintensities in the brains of bipolar patients which may be expected to have functional consequences even in the euthymic state [9], [24], [28].
There has also been growing interest in the cognitive impairments apparent during periods of remission in bipolar disorder. Deficits in executive function [10], [31], memory [3], [10], [27], [31] and sustained attention have been reported to occur during these periods [3]. We have recently found that of a large number of neuropsychological tests given to bipolar patients in an euthymic phase of their illness, only performance on a sustained attention task was impaired after controlling for low levels of affective symptoms [3]. This impairment was also present in a subgroup of younger patients, selected to be early in their illness course, suggesting that impaired sustained attention may be related to vulnerability to the disorder. The task used to assess sustained attention was the rapid visual information processing (RVIP) task from the CANTAB which requires subjects to detect three digit sequences (3–5–7, 2–4–6 and 4–6–8) in a stream of digits over a 7 min period [22]. As well as sustaining attention over a period of time, this task also requires the subject to hold in mind the three digit sequences. Hence, it remains possible that a deficit in working memory rather than sustained attention is at the heart of the persistent impairment in RVIP performance, especially given the impaired memory processes also reported to occur in this group [3], [10], [27], [31].
The present investigation, therefore, aimed to clarify whether the observed deficit in vigilance was also apparent in a task without a working memory component. Two tasks requiring sustained attention were developed, based on the Mackworth clock task [16], which placed either no demand upon working memory (WM− task) or contained a relatively high working memory load (WM+ task).
Section snippets
Subjects
The study was approved by Oxfordshire Psychiatric Research Ethics Committee. Thereby, 19 patients were recruited for this study from current registers of patients who had been admitted as in-patients and meeting DSM-IV criteria for Bipolar Disorder (American Psychiatric Association, 1994). All had been diagnosed with bipolar affective disorder by the treating physician for at least 2 years. Confirmation of diagnosis was made using the structured clinical interview for DSM-IV (SCID) axis I
Results
Group characteristics for the euthymic bipolar group and controls are displayed in Table 1. The two groups were matched for age, years of education, NART IQ and WAIS Block Design raw score. Despite very low scores on the HAM-D and Young scales, the euthymic bipolar group still scored significantly higher than controls on both measures.
The number of targets correctly detected was affected by group and task (group×task interaction: F(1,36)=4.5, P<0.05). Therefore, performance on the WM− and WM+
Discussion
We have previously found that euthymic patients with bipolar disorder showed persistent impairments in a sustained attention task with an additional small working memory component [3]. The results found in the present sample suggest that this deficit cannot be explained in terms of impaired working memory capacity. Euthymic patients with bipolar disorder were found to show robust impairments only on the sustained attention task based on a perceptual discrimination without working memory
References (31)
- et al.
Effects of lesions to ascending noradrenergic neurones on performance of a five-choice serial reaction task in rats; implications for theories of dorsal noradrenergic bundle function based on selective attention and arousal
Behavioural Brain Research
(1983) - et al.
Dementia: the estimation of premorbid intelligence using the National Adult Reading Test
Cortex
(1978) - et al.
Reductions in neuronal and glial density characterize the dorsolateral prefrontal cortex in bipolar disorder
Biological Psychiatry
(2001) - et al.
The functional neuroanatomy of mood disorders
Journal of Psychiatry Research
(1997) - et al.
Inhibition of both noradrenergic and serotonergic neurons in brain by the alpha-adrenergic agonist clonidine
Brain Research
(1975) - et al.
Declarative and procedural memory in bipolar disorder
Biological Psychiatry
(1999) - et al.
Cognitive function in euthymic bipolar I disorder
Psychiatry Research
(2001) - et al.
The neuropsychology and neuroanatomy of bipolar affective disorder: a critical review
Bipolar Disorder
(2001) - Clark L, Iverson SD, Goodwin GM, Sustained attention deficit in bipolar disorder. British Journal of Psychiatry, in...
- et al.
Prefrontal cortex involvement in acute mania: a neuropsychological investigation
American Journal of Psychiatry
(2001)
Forebrain norepinephrine: role in controlled information processing in the rat
Neuropsychopharmacology
The enduring psychosocial consequences of mania and depression
American Journal of Psychiatry
A fronto-parietal network for rapid visual information processing: a PET study of sustained attention and working memory
Neuropsychologia
Clonidine and diazepam have differential effects on tests of attention and learning
Psychopharmacology (Berlin)
Subgenual prefrontal cortex abnormalities in mood disorders
Nature
Cited by (105)
Abnormal functional connectivity strength in first-episode, drug-naïve adult patients with major depressive disorder
2020, Progress in Neuro-Psychopharmacology and Biological PsychiatryNeurocognitive profile of patients with Bipolar Affective Disorder in the euthymic phase
2019, Asian Journal of PsychiatryHigh-frequency repetitive transcranial magnetic stimulation (rTMS) improves neurocognitive function in bipolar disorder
2019, Journal of Affective DisordersPhysical activity modifies the association between depression and cognitive function in older adults
2019, Journal of Affective DisordersSelf-Reported Graphic Personal and Social Performance Scale (SRG-PSP) for measuring functionality in patients with bipolar disorder
2017, Journal of Affective Disorders