Executive Functioning in Women with Breast Cancer: A Longitudinal Examination of Intraindividual Variability in Reaction Time
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Cognitive symptoms are commonly reported by women diagnosed with breast cancer and have a negative impact on daily life. These cognitive changes are influenced by factors such as treatment (e.g., chemotherapy, hormone therapy), mood disruption, and even the cancer itself. In general, cognitive changes are subtle and affect multiple cognitive domains, although there is evidence that executive functioning may be particularly sensitive to the effects of breast cancer and its treatments. Most research in neuropsychology, including that with cancer populations, assesses mean performance level, which does not capture within-person variability. Intraindividual variability (IIV) is a different metric from measures of central tendency that examines fluctuations in task performance that are relatively transient and occur rapidly over short periods of time. IIV may provide novel information about cognitive functioning in cancer-related cognitive impairment. This dissertation first presents a systematic review of four specific cognitive subcomponents of executive function in breast cancer survivors: inhibition, set-shifting, working memory, and planning/decision making. Inhibition appears to be the subcomponent least affected by chemotherapy. Findings are mixed for set-shifting, working memory, and planning/decision making in part due to the heterogeneity in study methodologies. Next, two studies are reported which examine IIV in performance on a Stroop reaction time (RT) task as an indicator of cognitive functioning in women with breast cancer before and after chemotherapy compared to healthy controls assessed at similar time points. At baseline testing before surgery and neoadjuvant chemotherapy, breast cancer patients were more variable than healthy controls as task complexity increased (e.g., congruent vs. incongruent task conditions). Change scores from baseline to 1-month postchemotherapy were similar between patients and controls on all Stroop measures. From baseline to 9 months postchemotherapy, however, patients did not improve as much as healthy controls did and IIV was more sensitive than mean RT in detecting group differences. Self-reported cognitive symptoms increased from baseline to 9 months postchemotherapy, and change in symptoms associated with language and communication were positively correlated with change in variability. Taken together, the findings demonstrate that IIV is an important characteristic of cognitive performance in breast cancer patients.