Cognitive function in Uraemia: an examination using the working memory model

Abstract

Earlier studies have clearly shown that impairments in cognitive function exist in patients with chronic renal failure (Osberg et al., 1982). Speculations concerning the underlying cognitive processes that are affected in renal failure have involved short-term memory, general intelligence, visuo-spatial ability, and attention, with little consensus amongst researchers in any of these areas. A variety of methodological problems with most of these studies also make conclusions based upon them somewhat tenuous. The aim of this series of experiments was to provide a systematic hypothesis-testing approach to the examination of this issue, using the working memory model (Baddeley & Hitch, 1974) as a theoretical framework. Experiments 1 and 2 examined phonological loop and visuo-spatial sketchpad function in patients with renal failure. These studies showed that both of these components of working memory appear to be functioning normally when compared to healthy control subjects matched for age, sex, and education level. Experiment 3 used a dual task procedure to examine the hypothesis that a reduction in central executive functioning or capacity may be a factor in the impaired performance of renal patients on many tests of cognitive ability. This study also compared the performance of subjects with chronic renal failure with that of matched healthy control subjects, and found that renal patients performed significantly more poorly than controls when required to co-ordinate the performance of two tasks concurrently, a function which is assumed by the working memory model as requiring central executive resources. Experiment 4 tested the central executive hypothesis in greater depth, and also provided a comparison with groups of matched (non-renal) chronically ill subjects, and renal patients who had been receiving dialysis treatment for more than six months. This study showed a clear deficit in the performance of two concurrently performed tasks in non-dialysing renal patients in relation to all control groups. The healthy control, chronically ill control, and dialysing renal subject groups all performed at a similar level. The results of Experiment 4 indicate that the cognitive deficits evident in renal failure may be attributable, at least in part, to reduced functioning or capacity of the central executive component of working memory, and that this impairment may be largely reversed following regular, long-term dialysis treatment.