The role of frontal lobe function in working memory, inhibitory control, and processing speed in children with sickle cell disease

Sickle cell disease (SCD) is a chronic, hereditary condition that results in the abnormal “sickling” of red blood cells. Stroke is a common and debilitating complication of SCD and usually occurs for the first time between the ages of three and ten years. Previous research has demonstrated that the area of the brain most commonly affected by stroke is the frontal region. The frontal regions of the brain are thought to mediate abilities such as working memory, attention, and inhibitory control. Because stroke in children with SCD so often involves this brain region, this group provides an excellent opportunity to examine the cognitive effects of frontal lobe compromise during child development. The major purpose of this study was to compare three aspects of cognitive function (processing speed, inhibitory control, and working memory ability in both verbal and spatial domains) in children with SCD with and without frontal lobe damage associated with stroke. Processing speed, inhibitory control, and working memory function were each assessed with multiple tasks or task variants. Strong support was obtained for the existence of group differences on all three cognitive variables. An analysis of all of the speeded tasks that included the tasks used to measure inhibitory control, however, revealed that inhibitory control was not distinguishable from the slower processing speed associated with stroke. In addition to the quantitative differences between the groups, a predicted deficit in working memory function was observed in the stroke group. Specifically, whereas both groups were susceptible to domain-specific interference, only the stroke group was susceptible to non-specific (i.e., general) interference. This difference presumably reflects the negative effect of frontal lobe damage associated with stroke. In terms of Baddeley's (1986) theoretical model of working memory ability, susceptibility to general interference may reflect an impaired central executive. Alternatively, because general interference is observed in normal young children, the appearance of this deficit in the SCD children with stroke may reflect a failure of the working memory system to develop such that the two systems (verbal and spatial) fail to develop a normal level of independence.