Left angular gyrus disconnection impairs multiplication fact retrieval

Arithmetic fact retrieval has been suggested to recruit a left-lateralized network comprising perisylvian language areas, parietal areas such as the angular gyrus (AG), and subcortical structures such as the hippocampus. However, the underlying white matter connectivity of these areas has not been evaluated systematically so far. Using simple multiplication problems, we evaluated how disconnections in parietal brain areas affected arithmetic fact retrieval following stroke. We derived disconnectivity measures by jointly considering data from n=73 patients with acute unilateral lesions in either hemisphere and a white-matter tractography atlas (HCP-842) using the Lesion Quantification Toolbox (LQT). Whole-brain voxel-based analysis indicated a left-hemispheric cluster of white matter fibers connecting the AG and superior temporal areas to be associated with a fact retrieval deficit. Subsequent analyses of direct grey-to-grey matter disconnections revealed that disconnections of additional left-hemispheric areas (e.g., between the superior temporal gyrus and parietal areas) were significantly associated with the observed fact retrieval deficit. Results imply that disconnections of parietal areas (i.e., the AG) with language-related areas (i.e., superior and middle temporal gyri) seem specifically detrimental to arithmetic fact retrieval. This suggests that arithmetic fact retrieval recruits a widespread left-hemispheric network and emphasizes the relevance of white matter connectivity for number processing.

Language-dependent knowledge acquisition: investigating bilingual arithmetic learning

Previous studies revealed language-switching costs (LSC) in bilingual learning settings, consisting of performance decreases when problems are solved in a language different from that of instruction. Strong costs have been found for arithmetic fact knowledge. The aim of the present study was to investigate whether LSC in arithmetic also emerge in an auditory learning task and in pure fact learning. Furthermore, we tested whether LSC are influenced by the direction of language-switching. Thirty-three university students learned arithmetic facts of three different operations (i.e., multiplication, subtraction, artificial facts) over a period of four days. The training was either in German or English. On day five, participants solved problems in both languages. Results revealed LSC in response latencies for all three types of problems, independent of the direction of language-switching. These findings suggest that LSC are modality-unspecific and occur independent of the type of arithmetic fact knowledge.