Common neural substrates for ordinal numerical representations and ordinal representations in short-term memory

The current study explores the hypothesis that the neural substrates allowing for coding of ordinal information in the numerical domain also support the coding of order information in STM. We designed an fMRI experiment with 26 young adults that directly compared ordinal processing in numerical and STM tasks, by comparing the neural substrates of ordinal distance effects in numerical judgment and order STM tasks. Null conjunction analysis over the distance effects in both STM and numerical processing tasks confirmed that the IPS regions supporting the distance effects were indeed overlapping in both conditions and this overlap of neural activation in IPS areas was not driven by mere differences in task difficulty of the distances to be judged, since the distance effects in IPS regions for the STM and numerical tasks remained significant after controlling for any IPS activity related to non-ordinal distance judgment in the luminance control condition. These findings constitute a first direct demonstration of shared neural correlates for processing of order information in the STM and number domains, via the assessment of neural substrates associated with ordinal distance effects in both domains.