Language and calculation within the parietal lobe: a combined cognitive, anatomical and fMRI study

We report the case of a patient (ATH) who suffered from aphasia, deep dysle xia, and acalculia, following a lesion in her left perisylvian area. She sh owed a severe impairment in all tasks involving numbers in a verbal format, such as reading aloud, writing to dictation, or responding verbally to que stions of numerical knowledge. In contrast, her ability to manipulate nonve rbal representations of numbers, i.e., Arabic numerals and quantities, was comparatively well preserved, as evidenced for instance in number compariso n or number bisection tasks. This dissociated impairment of verbal and non- verbal numerical abilities entailed a differential impairment of the four a rithmetic operations. ATH performed much better with subtraction and additi on, that can be solved on the basis of quantity manipulation, than with mul tiplication and division problems, that are commonly solved by retrieving s tored verbal sequences. The brain lesion affected the classical language ar eas, but spared a subset of the left inferior parietal lobule that was acti ve during calculation tasks, as demonstrated with functional MRI. Finally, the relative preservation of subtraction versus multiplication may be relat ed to the fact that subtraction activated the intact right parietal lobe, w hile multiplication activated predominantly left-sided areas. (C) 2000 Else vier Science Ltd. All rights reserved.