Individuals who have this form of synesthesia involuntarily picture a map of numbers, where each is given a specific point and location in a line.

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•  This only occurs when the individual thinks of numbers
•  Mapping can change from person to person

In certain cases a number line can be described with intense clarity. The appearance and location of each digit can be described in great detail but other times the image is not so clear.

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Despite individual differences all number forms seem to have two characteristics in common:

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1. The map is unchanging with time 
2. Their possessors have no recollection of their beginning 



​It is hypothesized that there is cross activation in regions of  

1. ​Parietal Lobe 
2. Angular Gyrus ​

​Both are involved in numerical and spatial cognition