Davidson on Brain Basics

Neurons are the most basic cells in the nervous system, which includes the brain and spinal cord. Neurons are excitable, meaning that they process the body’s electrical and chemical signals. There are various kinds of neurons, each with a specialized function, all interconnected in astonishingly intricate ways. The adult brain has been estimated to contain over a hundred billion neurons, each of which fires several times a second and has several thousand connections to other neurons. There are over a million billion neural connections in your brain. That’s a lot of zeros.

Like so much else we believe we know, the basics of brain biology are often not what we think they are. In fact, for much of the twentieth century, it was believed that the number of neurons in the brain increased as we aged. It was thought that connections must expand in number in much the same way that we grow taller or gain more knowledge over time. That’s a logical assumption, but a false one. The way the brain actually works, then, is counterintuitive: An infant has more neurons, not fewer, than anyone old enough to be reading this book. Our little Baby Andrew has an excess of neurons. If his development unfolds as it should, he will lose 40 percent of his extra neurons before he grows up. If he does not, he will not be able to function independently in society and will be considered mentally handicapped or disabled. …

Canadian Donald O. Hebb is often called the father of neuropsychology because he was the first person to observe that learning occurs when neurons streamline into pathways and then streamline into other pathways, into efficient clusters that act in concert with one another. This is now called the Hebbian principle: Neurons that fire together, wire together. This means that the more we repeat certain patterns of behavior (that’s the firing together), the more those behaviors become rapid, then reflexive, then automatic (that’s the wiring). They become patterns, habits, groupings, categories, or concepts, all efficiencies that “wire together” sets of individual reflexes or responses. Reflexive behaviors combine into patterns so we don’t have to think about the components of each series of reactions each time we call upon them. …

Neural pathways connect the different parts of the brain and nervous system, translating ideas into actions in patterns learned over and over, reinforced by repetition, until they seem to us to be automatic. Repetitions literally shape specific patterns in very particular and extremely complex ways, coordinating impulses and activities across parts of the brain and nervous system that might be quite distant from one another. For example, the desire to walk and the ability to walk may seem automatic or natural to an able-bodied adult, but they are a complex operation involving many different parts of the brain that, with repetition, become more and more connected via neural pathways. To an infant, connecting the parts is a mysterious process. To a toddler, the process is clearer although not necessarily smooth. In those early stages, there are still many extraneous movements bundled into “toddling.” We are constantly correcting this process (as we correct everything little Andy does) by our reward system, applauding some behaviors, moderating others. …