Arithmetic skills are learnt in school and used up to old age. The question is whether the underlying processes of arithmetic change across the lifespan. This registered report (https://doi.org/10.1371/journal.pone.0256232) used functional near-infrared spectroscopy (fNIRS) in addition to behavioral measures (RT/ACC) to study the carry effect in two-digit addition and the borrow effect in two-digit subtraction in children (grade 3-4), younger adults (18-35 years) and older adults (above 60 years). Furthermore, processing speed, working memory, intelligence and math anxiety were assessed.

The zip-folder structure is explained in the METADATA.md file.