The mental number line and the human angular gyrus

To investigate the hemispheric organization of a language-independent spati al representation of number magnitude in the human brain we applied focal r epetitive transcranial magnetic stimulation (rTMS) to the right or left ang ular gyrus while subjects performed a number comparison task with numbers b etween 31 and 99. Repetitive TMS over the angular gyrus disrupted performan ce of a visuospatial search task, and rTMS at the same site disrupted organ ization of the putative "number line." In some cases the pattern of disrupt ion caused by angular gyrus rTMS suggested that this area normally mediates a spatial representation of number. The effect of angular gyrus rTMS on th e number line task was specific. rTMS had no disruptive effect when deliver ed over another parietal region, the supramarginal gyrus, in either the lef t or the right hemisphere. (C) 2001 Academic Press.