We learn a new word, or make a new friend, or taste a new dish, or undertake any of the innumerable things we do from day to day, and the experience is somehow etched into our brain and filed away in our mental world. If the experience is salient enough, it can be recalled again, even many years later, sometimes with amazing emotional vividness. It is the sum total of these personal experiences that makes each of us absolutely unique as individuals, since no one else could have had exactly the same experiences.
How does the brain do this? How does it take these bits and pieces of diverse experiences, and connect them together to build a coherent mental world?
When we recall an experience, often our language gets involved, with its nouns and verbs, syllables and intonations. But surely there isn't a miniature grammarian working away inside our brain, keeping a diary of our myriad activities, minute by minute. If there were, our inner grammarian would need another grammarian inside his brain to keep his diary, and so on ad infinitum.
So the brain must have its own distinctive language, nothing like the one you and I use. And obviously, being able to decipher the brain's language would have immense importance for our species, in particular for learning how we learn.
It is tempting to compare brains with computers, where any sound or image can be stored as long strings of ones and zeros. But that is only a very poor approximation of how the brain actually does things. The brain is vastly more complicated than any computer that has ever been built. We have only begun to study it scientifically since the start of the 20th century, when a Spanish doctor named Santiago Ramon y Cajal identified its most fundamental unit - the neuron.
According to the latest estimate, our brain has about 100 billion neurons, which communicate with each other across tiny spaces called synapses, not unlike switches in a digital circuit. Unlike digital circuits, however, the sender neuron releases tiny amounts of various chemicals into the synapses, called neurotransmitters, and these determine the behaviour of the receiver neurons.