Don't Choke : The Frontal Cortex:
"Interestingly, it turns out that simple differences in presentation can influence whether or not a math problem gets processed as a 'verbal' problem or as a 'spatial' problem. (More spatial problems, such as rotating an object in your mind, are more likely to be processed in the right PFC.) For instance, when an arithmetic problem is presented horizontally (84 - 18 = 66) it's seen as more verbal, since we're 'reading' the numbers from left to right, just like a sentence. In contrast, when a problem is presented vertically it's seen as more spatial:
84
-18
66
In other words, merely changing the presentation of the problem can dramatically alter how the brain processes the information."