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

Abstract

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.

Dissociation of subtraction and multiplication in the right parietal cortex: Evidence from intraoperative cortical electrostimulation

“…These visuospatial brain regions seem to play a major role in numerical magnitude processing . As reviewed in the Introduction section, this was supported by several lines of research employing different methodologies such as split-brain patient research (Cohen & Dehaene, 1996), fMRI (Chochon et al, 1999), and rTMS (R. Cohen Kadosh, K. Cohen Kadosh, Schuhmann, et al, 2007), although not by others (e.g., Sandrini et al, 2004). Because subtraction involves magnitude manipulation along the mental number line (e.g., Pica et al, 2004), it is likely to be subserved by the right parietal cortex (especially as compared to multiplication, which relies more on verbal processing as discussed earlier).…”

“…Andres and colleagues (2005) found significant increases in RTs when subjects were comparing digits following an rTMS-induced disruption in the left posterior parietal cortex. Sandrini et al (2004) also found that subjects' performance on a number-comparison task was significantly slowed down when trains of repetitive TMS were delivered to their posterior parietal scalp site overlying the left inferior parietal lobule.…”

“…Second, repetitive transcranial magnetic stimulation (rTMS) studies showed that stimulation in the left parietal cortex could induce dyscalculia (e.g., Andres, Seron, & Olivier, 2005;Knops, Nuerk, Sparing, Foltys, & Willmes, 2006;Sandrini, Rossini, & Miniussi, 2004). Andres and colleagues (2005) found significant increases in RTs when subjects were comparing digits following an rTMS-induced disruption in the left posterior parietal cortex.…”

“…For example, Gazzaniga and Smylie (1984) demonstrated that split-brain patients' right brain performed poorly on simple arithmetic tasks. A number of rTMS studies showed that stimulation in the left parietal cortex, but not that in the right parietal cortex, disrupted numerical processing (e.g., Andres et al, 2005;Sandrini et al, 2004). In addition, most reports on acquired dyscalculia came from patients with injuries to the left parietal regions (e.g., Ashkenazi et al, 2008;Baldo & Dronkers, 2007;Delazer & Benke, 1997, Denes & Signorini, 2001van Harskamp et al, 2002;see Dehaene & Cohen, 1997, for an exception).…”

The role of the angular gyrus in the modulation of visuospatial attention by the mental number line

“…Several neuroimaging findings indicate that the intraparietal sulcus (IPS) and the angular gyrus (ANG) in the posterior parietal cortex (PPC) are critically involved in numerical cognition (Cohen Kadosh et al, 2005;Pesenti et al, 2000;Pinel et al, 1999Pinel et al, , 2001Zago et al, 2001; for reviews, see Brannon, 2006;Dehaene, 2003;Rickard et al, 2000). Support for the role of these regions in numerical processing has also come from studies using transcranial magnetic stimulation (TMS) (Cappelletti et al, 2007;Göbel et al, 2001;Rusconi et al, 2005;Sandrini et al, 2004).…”