The Memory and The Mysterious Number Seven

Try doing the following test: ask a friend to make a list of ten words or numbers. Read it once. Then try to remember the items and say them aloud. Most people repeat a maximum of seven items.

Everything has to do with working memory, a type of short-term memory that functions as a blackboard where we write and delete information quickly before it becomes part of more permanent memory or disappear quickly. This mechanism is essential to have a conversation, touring a new city or simply dial a phone number. But space is limited. Specifically, it is limited to the “magical number seven”.

But why that number? Mikhail Rabinovich, a neuroscientist at the University of California at San Diego and Christian Bick, Germany’s Max Planck Institute, seem to have the answer. In an article published in November in the journal Physical Review Letters, the researchers present a mathematical model that explains how neurons are activated when registering a sequence of numbers or words. Under his scheme, for each item activates a group of neurons that inhibit the rest momentarily while retaining information, as well as he remembers. When longer a phrase or a string of numbers, the harder it is to keep inactive excited cells to other nerve cells. In particular, remember seven elements requires 15 times more “neuronal suppression” to remember three. And to remember ten o’clock we would need 50 times more capacity inhibition. Repeated more than ten digits or words using our temporary memory is physiologically impossible for almost all but the autistic, whose brain seems able to create circuits much stronger than that of a normal subject. “The brain is a complex biochemical machine,” says Rabonovich.