Colin Hamilton, Northumbria University. Why look at cognitive ... Malhi et al., 2007; Zubieta, Huguelet, O'Neil, & Giordani, 2001). In addition the visual span ...
Bipolar Affective Disorder and Working Memory: A Cognitive Psychologist’s Perspective Colin Hamilton, Northumbria University Why look at cognitive processes? For many cognitive psychologists the articulation of the cognitive processes under investigation is the primary, if not the sole motivation for the research. In contrast, clinical psychologists, clinicians and geneticists, whilst interested in the basic cognitive dysfunction may also prioritise how that knowledge may be applied within a treatment or intervention context (Antila et al., 2007; Bearden & Freimer, 2006; Gottesman & Gould, 2003; Mur, Portella, Martinez-Aran, Pifarre, & Vieta, 2007). I would argue that the inclusion of a cognitive psychology perspective within a multi-disciplinary approach would be of benefit to both clinicians and clinical psychologists in their exploration of cognitive dysfunction in Bipolar Affective Disorder. This brief overview of the cognitive approach to working memory is aimed at highlighting its putative contribution to the multidisciplinary understanding of the disorder. The Cognitive Psychology Perspective: The Construct of Working Memory Working memory is generally taken to be the „…means by which human beings maintain, manipulate and reinterpret on a moment to moment basis, information that is required for successful performance of a range of everyday tasks…” (Logie, 2003). The initial construct envisaged by Baddeley and Hitch ( Baddeley & Hitch, 1974) was composed of a tri-partite process, a central executive, a control process, coordinating the activity of two slave systems; a phonological loop and a non-verbal visuospatial scratchpad, verbal and non-verbal memory processes respectively. Whilst later conceptions of working memory tacitly accepted the notion of differentiated visual working memory and spatial working memory processes ( Baddeley, 1986), it was not until almost ten years later that the fractionation of the visuospatial component of working memory was formalised by Logie (1995). These multiple-resource accounts of working memory are in contrast to North American models where the conventional processes of maintenance and executive processing are considered to draw upon a single cognitive resource (Engle, Tuholski, Laughlin, & Conway, 1999; Unsworth & Engle, 2007). The figure below represents an integration of these varying perspectives. The majority of cognitive approaches to the construct of working memory place executive resources at the heart of the process. The executive resource not only coordinates slave system activity but provides functional support for the maintenance of information in the visual, spatial and phonological memory processes. The figure emphasises the central importance of executive resources to working memory, however the construct of executive function within working memory, like that of VSWM, has undergone substantial refinement (Baddeley, 2007). Baddeley (1986) identified four major functions for the executive resource; focused attention, divided attention between two concurrent tasks (dual-task co-ordination), switching attention from one task to another, and the integration of working memory with long term memory (LTM). Later work by Miyake and co-workers (Miyake et al., 2000) identified inhibitory, task-shifting and updating processes and related these to the clinically operationalised executive measures. Inhibition is correlated with the Tower of Hanoi performance, whilst task-shifting is related to the Wisconsin Card Sorting Task.
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Baddeley (2000) proposed another component to the executive processes, an Episodic Buffer which could maintain multi-modal information and facilitate binding of these discrete representations. The interface of working memory with a broader range of cognitive processes was also made explicit by Baddeley. A key element of this functional architecture consideration is that working memory support not only comes from endogenous working memory processes (in the top box) but in addition, extensive support is available from exogenous sources such as long term memory. Methodological Issues The dynamics of construct change can undermine the validity of established tasks in the field. This is particularly the case when there is a shift of emphasis away from the endogenous architecture to the more extensive functional architecture of working memory. To a significant extent this appears to have occurred in the clinical research investigating both visual and spatial working memory and executive function. A range of studies looking at working memory in affective disorders have drawn their tasks from established intelligence measures. The Forward Digit Span and Backward Digit Span procedures from the Wechsler Adult Intelligence Scale have been taken as verbal short term memory procedures (Antila et al., 2007; Fossati, Amar, Raux, Ergis, & Allilaire, 1999; Ilsley, Moffoot, & O'Carroll, 1995; Malhi et al., 2007; Zubieta, Huguelet, O'Neil, & Giordani, 2001). In addition the visual span procedure from the Wechsler Memory Scale ® has also been taken as a spatial short term memory task (Antila et al., 2007). It is likely that many of these tasks make demands upon the cognitive processes targeted in the research; however given the complexity of the functional architecture underlying working memory, it may also be presumed that many of these tasks also make demands upon some form of executive support and LTM resource (Unsworth & Engle, 2007). Thus the digit span task is affected by the familiarity and word frequency of the set, which are LTM factors. This is also the case for the visual or spatial span, an equivalent task to the Corsi Blocks task, which is known to demand extensive executive resources (Fisk & Sharp, 2003; Hamilton, Coates, & Heffernan, 2003; Rudkin, Pearson, & Logie, 2007; Vandierendonck, Kemps, Fastame, & Szmalec, 2004). Competent performance on these tasks does not necessarily compromise an inference, however when performance is impaired, a simple inference is likely to be undermined. If forward digit span task performance is impaired, where does the locus of the impairment reside? Does the deficit lie in the phonological loop process, executive resources or LTM support processes, or some combination of them? This also applies to impairment in the visual span or Corsi Blocks task. Recent research by Thompson and co-workers (2006, 2007) has adopted a cognitive approach in order to control for the potential confounds arising from the extensive functional architecture. Thus, Thompson et al (2006) concurrently measured executive resource efficacy and spatial working memory performance in euthymic patients with Bipolar Affective Disorder. They were then able to demonstrate that the patient group deficit in spatial working memory task, the Corsi task, was not a mnemonic impairment per se, but the consequence of impairment in the executive support for the task. This awareness of the contribution of the functional architecture has been evidenced in other clinical contexts (e.g. Vicari, Marotta, & Carlesimo, 2004). Research Implications Bearden and Freimer, (2006) have suggested that the motivation to identify endophenotypes arises, in part, from the “The inherent imprecision of psychiatric phenotyping…” (p306). This dissatisfaction with the DSM form of classification motivates a search for an intermediate trait which meets rigorous criteria including reliability, validity, moderately heritable, should be associated with causes rather than the effects of the disorder, and should vary continuously in the general population. Working Memory, with executive resources at its core would certainly meet many of these criteria. However, a consideration of the functional architecture underlying working memory necessitates a more discerning selection of tasks, a selection of tasks with greater construct validity than those conventionally employed. The danger for research would be to move from one context with issues in validity to another context, cognitive processes, which could be similarly constrained. As a part of a multi-disciplinary approach, cognitive psychology can inform the selection and the deployment of such tasks and also inform the inferences made from task performance and thus help remedy the validity issues inherent in the current literature.
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