The progressive breakdown of number processing and calculation ability: a case study.

We examined a retired Army General with Progressive Dementia whose initial major presenting complaint was dyscalculia. Our examinations revealed an orderly dissolution of calculation ability with differing dissociations in calculation ability apparent at progressive stages of cognitive decline. For example, we found that number reading and writing errors were qualitatively different from calculation errors. Numerosity knowledge and magnitude comparisons can remain intact even when other arithmetic knowledge and calculation abilities were grossly impaired. His decline in calculation abilities was first demonstrated on more complex problems (e.g., multiplication) and only in later stages on simpler (e.g., addition) problems. The patient was aware that aspects of his performance were impaired, but he was unable to state why--a dissociation between declarative and procedural knowledge.