Among the 100 million or so nerve cells in the brain, it turns out there is a group dedicated to making sense of numbers.
No one is born knowing their 1, 2, 3’s or A, B, C’s. However, the brain clearly handles these uniquely human but culturally varied types of knowledge differently. Many people, for example, are far stronger in one area or another, showing a propensity for verbal skills over numerical ones or vice versa.
So understanding how the brain codes these different systems could not only aid children with language disabilities, for instance, or those who struggle with processing numbers, but could also help to reveal more about how the brain works to process new information and acquire knowledge.
In a new study, which was published in the Journal of Neuroscience, researchers tested seven people with epilepsy who had electrodes implanted in their brains to determine the source of their seizures. Researchers have learned a great deal about the brain with the help of such patients, including more about how the brain works to produce speech and the effect of anesthesia on consciousness. The electrodes help inform doctors about the source of electrical disturbances that contribute to the seizures; some of these patients may then be eligible for additional surgery to remove the damaged region. Because of the unusual circumstance of having electrodes in their brain that can track neural activity, these patients are often approached to volunteer for clinical trials of brain function.
In the first experiment aimed at determining the brain’s “numeral area,” participants looked at single digits, letters, foreign numeral symbols from languages they didn’t know and at images of distorted numbers and letters that were unreadable. They were asked to press keys on the computer indicating whether or not they could read each symbol. In a second test, the volunteers saw either numbers, the words depicting numerals (one instead of 1) or words that sounded similar to number words (won instead of one), which they read aloud.
The researchers pinpointed a group of around 1 million to 2 million cells, located in a region called the inferior temporal gyrus that extends into both sides of the head near the ear canals. These cells responded much more strongly when the participants processed actual numbers than number words, meaningless symbols resembling the numbers or the numbers written in an unknown foreign language.
“This is the first ever study to show the existence of a cluster of nerve cells in the human brain that specializes in processing numerals,” Dr. Josef Parvizi, associate professor of neurology at Stanford University and the lead author of the study, said in a statement. “It’s a dramatic demonstration of our brain circuitry’s capacity to change in response to education. No one is born with the innate ability to recognize numerals.”
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Because the second experiment asked the participants to distinguish between phonetically similar words for the numbers (too instead of two) and the numerals, the researchers could determine that different brain regions were activated by the idea of the number, not just the sound of the word.
The authors say that the region of the brain that preferentially processes numerals is close to the area that is responsible for interpreting language, which makes sense since people often read words and numbers together. That could explain why previous work showed that some types of brain damage, for example, can interfere with reading letters but leave numeral reading unaffected, or can cause verbal dyslexia but not numerical confusion.
Interestingly, however, the cells responding to numerals seem to be physically close to those that process distorted numbers and to foreign number symbols, suggesting they might share a common origin and could be specialized versions of cells that generally process visual images of lines, angles and curves. Additional research on this region of cells could inform how education and learning tease out this subgroup of these cells to process numerals in particular.
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The study may also explain why such regions have not appeared in imaging studies of the brain that did not have the advantage of the implanted electrodes to track physiological activity. Since the inferior temporal gyrus is so close to the ear canals, functional MRI machines, which detect changes in oxygen use and blood flow by nerve cells, may not be as sensitive to the activity of neurons tucked away in that area.
However, say the researchers, combining different techniques should lead to deeper understanding of the brain’s inner workings and start to reveal some of its seemingly inscrutable mysteries.