Inhibitory deficits in aphasia
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People with Aphasia (PWA) often demonstrate deficits in higher order cognitive functions such as attention, executive function, and working memory that significantly interfere with their linguistic abilities. It is suggested that the basic cognitive function that underlies all other cognitive processes is inhibition, and it is defined as the potential to suppress pre-potent responses and select more optimal responses to perform efficiently in a challenging environment. The use of heart rate variability (HRV) to index inhibitory behavior in PWA has not yet been studied. HRV is a tool that represents the balance between the sympathetic and parasympathetic branches of the Autonomic Nervous System and reflects the change in cardiovascular activity as a response to increase in cognitive load. The goal of the present study is to determine whether inhibition can be physiologically indexed by HRV in PWA, and whether working memory (WM) is related to inhibitory behavior in PWA. Twelve PWA and 12 healthy age and education matched controls were assessed on two computerized experimental tests: 1) Continuous Performance Test-3 with greater inhibitory demands and 2) Continuous Performance Test-X with lower inhibitory demands. Physiological activity (time and frequency domain measures of HRV) was continuously recorded in five conditions: 1) baseline-10 minute rest, 2) first experimental test, 3) 10-minute between-task rest, 4) second experimental test, and 5) recovery-10 minute rest. N- back task was used as a measure of WM. On all the tests, PWA performance was significantly reduced (less sensitivity and greater response times) in comparison to healthy controls. Both participant groups demonstrated significant decrease in HRV indices with increase in inhibitory demands. This indicates that increase in inhibitory demands decreases parasympathetic activity to produce low HRV. Also, there is suppression of HRV during the experimental tasks compared to the baseline and recovery conditions in both groups. PWA demonstrate prolonged HRV recovery compared to healthy controls. Also, WM ability is associated with behavioral and physiological inhibitory performance in PWA. The results are consistent with Thayer and Lane’s Neurovisceral Integration model and suggest that HRV can potentially be used as an index inhibitory behavior in PWA.