In their experiments, the researchers also used the adaptation phenomenon, that the brain adapts to stimuli by reducing its initial activity--and that repeating the same quantity leads to reduced activation compared to changing the quantity. They asked subjects whose brains were being scanned using fMRI to view consecutive numbers presented on a screen that represented either the same or different quantities. Crucially, the numbers were also presented either as two words (e.g., two or eight), two digits (e.g., 2 or 8), or a mixed notation (two and 8).
They hypothesized "that if the assumption of an abstract representation of numbers in the [parietal cortex] held true, the adaptation effect would be observed within and across notations. In contrast, in the case of nonabstract numerical representation, we expected that the adaptation effect would be modulated by the notation type. This result would suggest that distinct neuronal populations for notation exist." This meant that if the brain region was purely representing an abstraction of a number (e.g., 8) then any notational representation of this number (e.g., 8 or eight) would cause an adaptation effect. Alternatively, if a brain region processed a specific nonabstract number (e.g., 8) then adaptation would only be seen for the same notation (e.g., 8 but not eight).
Their analysis revealed an effect of notation in the right parietal lobe, showing that this region appears to harbor neurons that process nonabstract numerical representations, in addition to neurons that code for abstract representations of numeric quantities.
The researchers said that exploring how the processing of numerical symbols develops could have cli