Distinct neural mechanisms for reading Arabic vs. verbal numbers: An ERP study

In this electroencephalogram/event-related potential (EEG/ERP) study, 16 volunteers were asked to compare the numerical equality of 360 pairs of multidigit numbers presented in Arabic or verbal format. Behavioural data showed faster and more accurate responses for digit targets, with a right hand/left hemisphere advantage only for verbal numerals. Occipito-temporal N1, peaking at approximately 180 ms, was strongly left-lateralized during verbal number processing and bilateral during digit processing. A LORETA (low-resolution electromagnetic tomography) source reconstruction performed at the N1 latency stage (155-185 ms) revealed greater brain activation during coding of Arabic than of verbal stimuli. Digit perceptual coding was associated with the activation of the right angular gyrus (rAG), the left fusiform gyrus (FG,BA37), and left and right superior and medial frontal areas. N1 sources for verbal numerals included the left FG (BA37), the precuneus (BA31), the parahippocampal area and a small right prefrontal activation. In addition, verbal numerals elicited a late frontocentral negativity, possibly reflecting stimulus unfamiliarity or complexity. Overall, the data suggest distinct mechanisms for number reading through ciphers (digits) or words. Information about quantity was accessed earlier and more accurately if numbers were in a nonlinguistic code. Indeed, it can be speculated that numerosity processing would involve circuits originally involved in processing space (i.e., rAG/rIPS).