On March 6th, 2016 we learned about

Finding where our brain works with figures

Today my first grader saw the Roman numeral “III” alongside instructions about numbers, and assumed it was 111. It was a reminder that numbers are often dealt with through abstract representations of actual (or imaginary!) quantities. While counting quantities of objects can be done without being able to write about it, the way we read and understand numbers is still a work-in-progress. Two recent studies found some unexpected wrinkles in how, and where, our brain handles numbers.

Recognizing known numbers

With two hemispheres and many specialized structures, figuring out where our brains process numbers hasn’t been easy. There’s been a longstanding assumption that with many language functions being handled on the left side of the brain, numerical reasoning was left mostly to the right. Working with numbers isn’t a single function though, and it looks like just the act of reading numbers is processed in visual number form areas (NFAs) in both of the brain’s hemispheres. Similar to the act of deciphering written letters, fMRI scans of test subjects looking at familiar numerals as well as gibberish or modified characters showed that known numerals consistently activated areas at the underside of both the left and right temporal lobes, whereas other characters did not.

Sorting size on each side

This isn’t to say that mathematical concepts are equally distributed across our heads. A separate study looked at how our brains handle some basic numerical comparisons, and some biases between the two hemispheres were found. Researchers noted that in stroke victims who had lost functionality in one hemisphere or the other, basic comparisons between larger and smaller quantities seemed to be affected by where their brain damage had occurred. Rather than damage anyone, the scientists instead created a right/left bias by stimulating one hemisphere or the other in healthy patients. This was done with what’s called a caloric reflex test, which is a strange combination of viewing a horizontal or vertical line through marked goggles, and then dribbling hot or cold water into one ear. This is usually used for other diagnostic purposes, but it gave the researchers a way to create a temporary bias in participants’ cognition.

Once activated, participants had some interesting biases in how they compared numbers. If the left side of the brain was stimulated, they’d favor higher numbers, while the right side of the brain seemed to pull people towards lower numbers. For example, if asked to pick a number at the midpoint of 50 to 100, active left hemispheres tended to select numbers above 75, while activated right hemispheres picked something below 65. The exact quantities weren’t the key here, but just the high-low comparisons. This was seen when the same test subjects were asked to draw analog clocks, and then drew either 1-6 or 7-12 in slightly larger, clearer characters correlating with whichever hemisphere was stimulated.

While people occasionally reveal this kind of preference without water in their ears, this research isn’t looking to help people predict each other’s favorite number. Aside from helping us piece together how the brain works with math in general, it also has applications for people with brain damage, helping us identify where the damage occurred and what functions will need to be treated.

Source: Big and small numbers are processed in different sides of the brain, Scienmag

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