Alex's Adventures in Numberland - Alex Bellos [16]
Nieder decided he wanted to see what was happening in the monkeys’ brains hey were holding the number in their heads. So, he inserted an electrode two microns in diameter through a hole in their skulls and into the neural tissue. Don’t worry, no monkeys were hurt. At that size, an electrode is tiny enough to slide through the brain without causing damage or pain. (The insertion of electrodes into human brains for research contravenes ethical guidelines, although it is allowed for therapeutic reasons such as the treatment of epilepsy.) Nieder positioned the electrode so that it faced a section of the monkeys’ pre-frontal cortex, and then began the experiment.
The electrode was so sensitive that it could pick up electrical discharge in individual neurons. When the monkeys thought of numbers, Nieder saw that certain neurons became very active. A whole patch of their brains was lighting up.
On closer analysis, he made a fascinating discovery. The number-sensitive neurons reacted with varying charges depending on the number that the monkey was thinking of at the time. And each neuron had a ‘preferred’ number – a number that made it most active. There was, for example, a population of several thousand neurons that preferred the number one. These neurons shone brightly when a monkey thought of one, less brightly when he thought of two, even less brightly when he thought of three, and so on. There was another set of neurons that preferred the number two. These neurons shone brightest when a monkey thought of two, less brightly when he thought of one or three, dimmer still when the monkey thought of four. Another group of neurons preferred the number three, and another the number four. Nieder conducted experiments up to the number 30, and for each number found neurons that preferred that number.
The results offered an explanation for why our intuitions favour an approximate understanding of numbers. When a monkey is thinking ‘four’, the neurons that prefer four are the most active, of course. But the neurons that prefer three and the neurons that prefer five are also active, though less so, because its brain is also thinking of the numbers surrounding four. ‘It is a noisy sense of number,’ explained Nieder. ‘The monkeys can only represent cardinalities in an approximate way.’
It is almost certain that the same thing happens in human brains. Which raises an interesting question. If our brains can represent numbers only approximately, then how were we able to ‘invent’ numbers in the first place? ‘The “exact number sense” is a [uniquely] human property that probably stems from our ability to represent number very precisely with symbols,’ concluded Nieder. Which reinforces the point that numbers are a cultural artefact, a man-made construct rather than something that we acquire innately.
CHAPTER ONE
The Counter Culture
In Lincolnshire during medieval times, a pimp plus a dik got you a bumfit. There was nothing dishonourable about this. The words were simply the numbers five, ten and fifteen in a jargon used by shepherds when counting their sheep. The full sequence ran:
Yan
>
Tan
Tethera
Pethera
Pimp
Sethera
Lethera
Hovera
Covera
Dik
Yan-a-dik
Tan-a-dik
Tethera-dik
Pethera-dik
Bumfit
Yan-a-bumfit
Tan-a-bumfit
Tethera-bumfit
Pethera-bumfit
Piggot
This is a different way from how we count now, and not just because all the words are unfamiliar. Lincolnshire shepherds organized their numbers in groups of twenty, starting counting with yan and ending with piggot. If a shepherd had more than twenty sheep – and provided he hadn’t sent himself to sleep – he would make note of having completed one cycle by putting a pebble in his pocket, or making a mark on the ground, or scraping a line in his crook. He would then start from the beginning again: ‘Yan, tan, tethera…’ If he had 80 sheep, he would have four pebbles in his pocket, or have marked four lines, at the end. The system is very efficient for the shepherd; he has four small items to represent 80 big