The breakdown of calculation procedures in Alzheimer's disease

The study investigates calculation abilities in 12 patients with probable A lzheimer's disease (AD) and compares them to calculation abilities of healt hy control subjects (NC) and patients with focal left hemisphere lesions (L HL). AD patients scored significantly lower than NC in all calculation task s and lower than LHL patients in the execution of complex written calculati on, but not in the retrieval of arithmetic facts. In the AD group a subject -by-subject error analysis on the complex written calculation showed a low consistency and a high variability of error types. It is suggested that AD patients' difficulties in complex calculation arise from a monitoring defic it and not from incomplete or distorted calculation algorithms. Overall, de ficits in monitoring calculation procedures may be an early and common symp tom of AD.