However, to unambiguously establish that the subjects' brains were really reacting to numerical quantity, the researcher occasionally injected a "deviant stimulus" into the second presentation of a quantity as the brain was adapting to it. This deviant stimulus consisted of a different number that was either close to, or far from, the number being presented. The researchers found that this deviant quantity interrupted adaptation more if it was distant from the adaptation quantity than if it was closer--conclusive evidence that the subjects were processing numerical quantities.
The researchers concluded that their findings "indicate an important role for parietal cortex in the coding of symbolic and nonsymbolic quantities."
They also concluded that "crucially, we observed crossnotation adaptation and recovery, particularly in the right parietal cortex, supporting the idea that shared neural populations encode nonsymbolic quantities and symbolic stimuli." Piazza and colleagues also concluded that their findings shed light on how the brain learns to associate symbols with numbers.
"Our results show that, at least in the adult brain, numerical symbols and nonnumerical numerosities converge onto shared neural representations," they wrote. "Perhaps we attach meaning to symbols by physically linking populations of neurons sensitive to symbol shapes to preexisting neural populations holding a nonsymbolic representation of the corresponding preverbal domain (e.g., numerosity)."
In the other paper in Neuron, Roi Cohen Kadosh and colleagues conducted experiments demonstrating that the two hemispheres of the parietal lobe function differently in processing numbers. While the left lobe harbors abstract numerical representations, the right shows a dependence on the notation used for a number, they found. The researchers concluded that "results challenge the commonl