Ask any four-year-old child for his age, and chances are he will hold up four fingers.

He will count and add with his fingers too, and this is true for children all over the world. To count with your fingers, you need to be able to move each separately, a skill not found in all mammals. In fact, most non-primates cannot move the individual digits on their hands, feet or paws. This skill requires direct connections from the neurons in the motor cortex in the brain to the motoneurons in the spinal cord that excite your finger muscles. So - is our system of counting and calculating dependent upon our particular brain-to-finger circuitry?

Observations of people with Gerstmann's syndrome may help answer this question. Individual with this disorder suffer from "finger agnosia." If you touch one of their fingers, they may not be able to identify which finger was touched. In addition, some have trouble performing basic calculations, such as simple addition or subtraction. The area in the brain that underlies our ability to count and calculate is located close to the area that processes information from our fingers, and these regions may be damaged in individuals with Gerstmann's syndrome. Here again we see a connection between our ability to use our fingers and to count.