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There are some people—incredibly intelligent people, no less—for whom a grasp of numbers is entirely elusive. Is 6 bigger than 5? What is halfway between 200 and 400? If I give you $10 for a $7.50 purchase, what is my change? If answering these and similar questions, not exactly feats of mathematical expertise of the highest order, is difficult and frustrating, that could be, says Ewen Callaway in Nature, a sign of a neurological discrepancy known as dyscalculia.

Affecting somewhere from 2.5 to 7.5 percent of the population, dyscalculia, “sometimes called number blindness and likened to dyslexia for maths,” won’t just preclude you from a happy career in accounting but can actually make day-to-day life strenuous. Time:

Though you may have never heard of it, the condition is much more than being bad at math. “You need to hear people suffering from dyscalculia, how hard it is for them to do everyday things, just going to the shop, counting change,” says Roi Cohen Kadosh, a research fellow at University College London (UCL). Other practical impossibilities for dyscalculics: balancing a checkbook, planning for retirement, being a baseball fan. The list goes on.

According to recent research, dyscalculia—and, hence, math ability in general—is tied to particular brain regions. In people with normal math ability, these regions can be temporarily turned on and off. According to Callaway, math ability is just as innate a part of being human as sight, vision or any other sense.

Like nearly all human cognitive abilities, number sense is evolutionarily ancient — tens if not hundreds of millions of years old. Studies of chimpanzees, monkeys, newborn chicks, salamanders and even honeybees point to two parallel systems for representing quantities. One, called the approximate number sense, distinguishes larger quantities from smaller ones, be they dots flashing on a screen or fruits in a tree. Studies on monkeys reveal that certain neurons in a specific fold of the parietal lobe fire more vigorously in response to increasingly higher numbers. A second ancient number system allows humans and many other animals to instantly and precisely recognize small quantities, up to four. Primate studies show that individual neurons within the same fold, called the intraparietal sulcus, seem tuned to particular quantities, such that when a monkey is performing a task that involves numbers, one neuron will fire for the number 1, a different one will fire for 2 and so on.

People who are poor at distinguishing approximate quantities do badly in maths, suggesting that the approximate-number system is crucial. And some work shows that dyscalculics are poor at recognizing small numbers, suggesting that this ability is also fundamental to numeracy. Moreover, scans of people with dyscalculia suggest that their intraparietal sulci are less active when processing numbers and less connected with the rest of the brain compared with numerate children and adults.

Other recent research suggests that for most people who like to claim they are bad at math the issue has to do more with motivation than intelligence. But, for those with dyscalculia, the struggles are much more fundamental and, says Callaway, may be consequences of an underlying issue affecting dyscalculics. Research by Brian Butterworth suggests that, “another cognitive capacity is even more fundamental to number sense.”

He calls this ‘numerosity coding’: the understanding that things have a precise quantity associated with them, and that adding or taking things away alters that quantity.

Butterworth thinks that if researchers can better understand the root causes of dyscalculia, they can craft training programs, including specialized games, that can be used to help people hone their number sense.

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