Evidencing inhibitory deficits in Alzheimer's disease through interference effects and shifting disabilities in the Stroop test.

To investigate the contribution of inhibitory deficits in the deterioration of executive function abilities in Alzheimer's disease (AD), a modified version of the Stroop test was submitted to 44 AD patients and 44 elderly controls. Half of the subjects performed successively the Interference Stroop task, the two control tasks and the Reverse Stroop task, and half performed the Reverse Stroop task, the control tasks and finally the Interference Stroop task. This experimental design allowed to assess inhibitory deficits by measuring classical interference effects but also by measuring the ability to shift between tasks instructions. Results confirmed AD patients' difficulty in suppressing the automatic response of reading in the Interference Stroop task. Moreover, AD patients presented worsened performances in the Interference task when administered after the Reverse task, and a Reverse Stroop effect was found in the patients revealing their difficulty in suppressing a previously relevant rule in order to learn a new one.