I want you to do a little experiment.
Hold out your right hand horizontal in front of you, making sure to leave a gap between each finger. While keeping your hand as relaxed as possible, bend your thumb inward so that it touches, or nearly touches, your palm. As you do this, watch the tip of your index finger? Does it involuntarily move or twitch? Chances are that you will find it hard to move your thumb without there also being some movement in your index finger.
Given what we know about the principle of ‘fire together wire together’ this is not surprising. When we first start using our fingers as babies, most of the activities we do with our thumb are also activities that we do with our index finger. One of the first things a baby does with her fingers is to grasp hold of objects, whether it be a toy or the hand of a parent. In a normal grasping action, our thumb and index finger are usually the first to make contact, which they do almost simultaneously. By contrast, the two fingers that probably arrive on things with the greatest duration between are the thumb and the pinky.
As a result of this, the mind maps which control the thumb and the index finger will tend to be very close together, and even work in conjunction. When the neurons which control one action fire up in the brain, chances are that the neurons which control the other will also fire up.
This isn’t just theory, but has been proved in the lab. Norman Doidge, whose best-selling book on neuroplasticity we will have frequent occasion to quote, chronicles various experiments performed by the neuroscientist Michael Merzenich:
“In one ingenious experiment, Merzenich mapped a normal monkey’s hand, then sewed together two of the monkey’s fingers, so that both fingers moved as one. After several months of allowing the monkey to use its sewn fingers, the monkey was remapped. The two maps or the originally separate fingers had now merged into a single map. If the experimenters touched any point on either finger, this new single map would light up. Because all the movements and sensations in those fingers always occurred simultaneously, they’d formed the same map. The experiment showed that timing of the input to the neurons in the map was the key to forming it—neurons that fired together in time wired together to make one map.”
Elsewhere in the book Dr. Doidge explains why is going on physiologically when the fire together wire together phenomenon is happening:
“When we perform an activity that requires specific neurons to fire together, they release BDNF. This growth factor consolidates the connections between those neurons and helps to wire them together so they fire together reliably in the future. BDNF also promotes the growth of the thin fatty coat around every neuron that speeds up the transmission of electrical signals.”