Abstract
Recent neuro-imaging research identified the bilateral intraparietal sulcus (IPS) to be a key area associated with number processing. However, causal structure-function relationships are hard to evaluate from neuro-imaging techniques such as fMRI. Nevertheless, brain stimulation methods like transcranial direct current stimulation (tDCS) allow for investigating the functional relevance of the IPS for number processing. Following up on a study using bilateral bi-cephalic tDCS over the IPS, the current study aimed at evaluating the differential lateralized functional contributions of the left and right IPS to number processing using unilateral bi-cephalic tDCS over either the left or right IPS. Results indicated a right lateralization for the processing of the place-value structure of the Arabic number system. Importantly, the processing of number magnitude information was not affected by unilateral IPS corroborating the assumption that number magnitude is processed in the bilateral IPS. Taken together, these data suggest that even though number magnitude is represented bilaterally, the left and right IPS seem to contribute differentially to numerical cognition with respect to the processing of specific other aspects of numerical information.
Highlights
Magnitude information is the most important information conveyed by Arabic numbers (Shepard et al, 1975; Miller and Gelman, 1983; Miller and Stigler, 1987, 1991)
ADDITION TASK In a first step, running the linear mixed effects model (LMM) including only the effect of stimulation revealed that the effect of stimulation on reaction time (RT) was not significant indicating that overall RT were not influenced by stimulation (right anodal: 2788 ms, left anodal: 2739 ms, sham: 2722 ms, right cathodal: 2693 ms, left cathodal: 2714 ms; F(4,23.93) = 0.38, p = 0.819)
The analyses revealed reliable main effects of carry-over, distractor distance and target identity indicating that responses were faster when (i) the problem did not require a carry-over, (ii) distractor distance was large, and (iii) the target was the correct result of the problem
Summary
Magnitude information is the most important information conveyed by Arabic numbers (Shepard et al, 1975; Miller and Gelman, 1983; Miller and Stigler, 1987, 1991). There is accumulating evidence from both, patient studies as well as functional neuro-imaging studies that the bilateral intraparietal sulci (IPS) are a core region for number magnitude processing. In a two-digit addition task participants had to choose the solution probe from two alternatives, which was either identical with the correct result or closest to it. The authors manipulated the factors target identity and distractor distance. In line with recent data on mental arithmetic, influences of target identity were— among others—associated with fMRI signal change in and around the bilateral IPS as were influences of distractor distance and carry-over
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