Abstract
Functional lateralization is established for various cognitive functions, but was hardly ever investigated for arithmetic processing. Most neurocognitive models assume a central role of the bilateral intraparietal sulcus (IPS) in arithmetic processing and there is some evidence for more pronounced left-hemispheric activation for symbolic arithmetic. However, evidence was mainly obtained by studies in right-handers. Therefore, we conducted a functional near-infrared spectroscopy (fNIRS) study, in which IPS activation of left-handed adults was compared to right-handed adults in a symbolic approximate calculation task. The results showed that left-handers had a stronger functional right-lateralization in the IPS than right-handers. This finding has important consequences, as the bilateral IPS activation pattern for arithmetic processing seems to be shaped by functional lateralization and thus differs between left- and right-handers. We propose three possible accounts for the observed functional lateralization of arithmetic processing.
Highlights
Functional lateralization is established for various cognitive functions, but was hardly ever investigated for arithmetic processing
As the region of interest (ROI), we focused only on the bilateral intraparietal sulcus (IPS) being located between the superior parietal lobule (SPL) and inferior parietal lobule (IPL), i.e., channel L8 corresponding to the left IPS and channel R17 corresponding to the right IPS
The results yielded no significant correlation between error rate (ER) and laterality index of functional brain activation (LIbrain) of left- and right-handers [r(43) = −0.15, p = 0.326], suggesting that the difference for LIbrain reported below does not seem to be influenced by the difference in performance between the groups
Summary
Functional lateralization is established for various cognitive functions, but was hardly ever investigated for arithmetic processing. Handedness describes the preferential use of one of the hands with high accuracy and motor speed while performing skilled (i.e., culturally influenced activities such as handwriting) and unskilled actions based on spontaneous activities (e.g., picking up items)[1] Both right- and left-handers represent the normal range of human diversity, but they differ in processing of various types of information and in the functional lateralization of the brain[2]. Brain stimulation studies confirmed the functional role of the bilateral IPS in arithmetic processing and more basic number processing[22,23,24] with a larger involvement of the left IPS22,25,26 compared to the right IPS27. Different involvement of the left and right IPS were further found for approximate compared to exact calculation, while approximate calculation was found to be associated with stronger bilateral IPS activation than exact calculation[28,30,31]
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