The differential involvement of inferior parietal lobule in number comparison: a rTMS study

Number processing is known to involve several sites within the posterior regions of parietal cortex. Here, we investigated whether neural activity in the inferior parietal lobule (IPL) is essential for number processing, by observing the effects of interfering with its activity during the execution of a standard number comparison task. Subjects performance on the task was significantly slowed down when we delivered trains of repetitive transcranial magnetic stimuli (rTMS) to the posterior parietal scalp site overlying the left IPL, while rTMS did not affect the number comparison task if delivered to homologous, contralateral (right) IPL. In conclusion, the present findings add support to a growing body of evidence from neuropsychology and neuroimaging studies that the left inferior parietal lobule is an important component of the networks subserving the representation of quantity.