Imagine you're living in Maine and want to drive to a relative's house in Florida, but your only map is the map of the United States that used to fit in your binder in Junior High. You can see where Florida is in relation to Maine, and may see where a few major cities and highways are, but once you get to Florida, you can only guess where your relation's house will be.
That sums up the current state of knowledge of the inner workings of the human brain. What we know about brain function comes from various imaging techniques that give us maps of major activity in the brain when a subject busy recalling memories or listening to music. In color-enhanced images, different parts of the brain "light up," when a subject is reading than when the subject is sniffing certain scents or listening to Beethoven's Sixth. Even more interesting is that different parts "light up" when an ordinary person listens to Beethoven's Sixth than when a professional musician listens to the same piece, since the professional musician listens with a different understanding of the music.
What imaging techniques can't do is pinpoint with absolute precision just how groups of neurons "talk" to one another in recalling memories, processing sensory information, sending signals to the muscles, or spinning out complex thoughts about thought itself. What's astonishing is how much knowledge neuroscientists have pieced together from such subtle data, though the scientists themselves will be the first to tell you that we are still far, far from understanding exactly how the human brain works. From what they've learned so far, though, the rest of us can draw useful lessons on the care and feeding of the human brain.
THE BRAIN IS FLEXIBLE
A preserved sheep's brain, sitting in the bottom of a dissecting pan, doesn't convey much about the dynamism of the living brain. To the student, poking at the brain with a dissecting probe, there are few landmarks. The cerebellum sits in the back, where it controls many motor functions and stores motor memory. The cerebrum, the most prominent part of the brain in mammals, sits in the front, processing sensory and motor information, storing memories, and allowing its owner - when it was still alive - to think. A corpus callosum connects the two hemispheres of the brain and coordinates information flow between the two halves. A careful student can pick out the thalamus, hypothalamus, and pituitary structures involved in maintaining homeostasis in the body, and perhaps the amygdala and hippocampus, essential structures in creating and storing memories.
So much for the information that can be obtained by dissection. What the student may notice is that unlike the diagrams of the brain in the textbook, there are no convenient colored bands and patches to show which parts of the cerebrum process sound, sight, smell, or any of the other sensory information. Anatomically, even at the cellular level, these segments look no different from one another. This led Vernon Mountcastle, a neuroscientist at Johns Hopkins University, to suggest in 1978 that these areas of the brain actually process information in exactly the same way, regardless of what kind of sensory information is being processed. Yes, to us it seems as though sight, sound, hearing, and all the other senses all have different qualities. And they are different, coming from different environmental cues. Yet the way our cortex processes these signals from our various sense organs are all essentially the same. So could, say, the visual cortex in the back of the brain process sound signals from the ears. It certainly could - and does, as later researchers found when working with subjects who had lost their sense of sight. If the brain were hardwired, so to speak, to process certain sensory information in certain parts of the cortex, then people who lost their sense of sight should have no activity in the visual cortex at the back of the cerebrum. Yet our bodies have a better sense of efficiency than that, and aren't about to let any area of the valuable brain to go waste. The visual cortex in blind subjects does light up as their brains rewire themselves to use the visual cortex to process sound signals. Likewise, subjects who were born deaf or lost their hearing later in live use their auditory cortex to process signals from the eyes. Brain rewiring has been documented in stroke victims as well, depending on the severity and location of the stroke.
Hence we know that the brain is not fixed at adulthood. Throughout our lives we can continue to use and improve our brains, even rewiring the brain if necessary. We needn't lose one of our senses to experience brain rewiring. Brain studies have shown that when depressed patience undergo cognitive therapy and learn to purposely change their thoughts, their brains undergo physical changes. As old habits of rehearsing the same old depressive thoughts are replaced by new, deliberate thoughts, the brain itself responds by changing the connections. There may be something to the idea of thinking positive thoughts to change your life.
THE BRAIN GROWS WITH EXERCISE
There's another useful lesson we can learn from the brain flexibility studies: the brain grows with mental exercise.
Neural researchers have long known that we're born with all the nerve cells in our brains that we'll ever have. Yet the brain keeps growing throughout the first ten years of life. So what exactly is growing? We're not adding new brain cells. What's happening is we're growing dendrites, the little branches of our nerve cells that connect one to the other. The growth happens in response to stimulation, so rest assured that all those trips to the museum with the kids really are good for their brains. Anything that varies their environment and allows them to interact with other people is good, and physical interaction with the environment rather than passively watching the world go by is the best stimulus for brain growth.
But growth doesn't stop even at age ten. While it slows considerably after childhood, brains do continue to grow. One area of the brain, Wernicke's area, is strongly associated with word understanding. College-educated adults have many more dendrites in this area of the brain than adults of the same age with only a high school education or less. Does a college education make dendrites grow, or are people with more dendrites in Wernicke's area more likely to finish college? While the jury is still out on this question, evidence is increasingly showing that the larger Wernicke's area is due to growth under the stimulus of continuing education.
The take-home message here is one you may have heard: use it or lose it. Adult brains may not grow as fast as child brains, but like muscles, they continue growing and developing when they're exercised. If you want to be sharp in old age, exercise your brain. Don't just veg in front of the T.V. or the video game machine. Educational programs or puzzle-type games are good, but you also need some physical interaction with the environment. Learning new physical skills, such as a new sport or craft, challenge the brain to grow. Travel is good, too, since it requires you to navigate new, unfamiliar spaces with different visual cues.
MEMORIES ARE COMPLEX - AND THAT'S A GOOD THING
Let's return to that sheep's brain in the dissection pan. Beneath the cerebrum, the patient, skillful anatomy student may be able to tease out a pair of lumpy bits called the amygdala and a pair of seahorse-shaped structures, the hippocampus. While they don't look like much, these two structures are critical in memory formation. The amygdala may tie memories retrieved by the hippocampus to emotions from the limbic system, or may be a site of emotional memory itself - ideas differ on this point. Whichever its role, the amygdala is critical in the fight-or-flight response to danger. The hippocampus is involved in long-term memory formation. Patients with damage to the hippocampus may be able to process information in working memory, but can't form new memories and recall them later. Exactly how the brain forms memories is not understood. New information from researchers at the University of California at Irvine lends gives us a few more clues.
Researcher Melina Uncapher and her colleagues used brain imaging technology to examine how people retrieve memories. Subjects studied words on a screen, and were later asked to recall the word, its color, position, and whether it was an old word studied in a prior session or a new one. They found that different regions of the brain were involved in processing the words themselves, their color, and their position. What's more, when subjects recalled all of the features, not just color or location, another area of the brain lit up: a bit known as the intraparietal sulcus. This little slip of neural tissue seems to be involved in binding together the various features of a particular memory - color, sight, sound, etc. - and package it together.
Other studies have shown that associations with the same memory seem to make the memory more retrievable. A memory made up of a many bits of sensory information, or a single fact linked with other facts, becomes part of a network of remembered pieces. Just like a net, when you pull on one part, the rest of the net comes with it.
What does this mean for us? The more associations we make with some fact we want to remember, the more likely it is that we can retrieve that fact. This is why many memory devices, such as mnemonic devices, really work. By associating numbers with strong visual images, it's easier to recall the numbers. If you're busy memorizing vocabulary for next week's anatomy quiz, go a step beyond flash cards to memorize individual words. Find conceptual links between vocabulary terms, so that recalling one helps you recall others. Use pictures to create a visual link between a term and its meaning. Say the words and their definitions aloud, or create rhymes or songs to help pull them out of auditory memory.
The more that neuroscientists learn about the human brain, they more ways they discover to help us keep our brains young, active, and sharp. With luck, science may find cures for devastating disorders of the memory, such as amnesia or dementia. For those who are blessed with healthy brains, neural science offers new ideas for helping preserve and enhance brain health and function all our lives.
Now - get up out of your chair and go exercise your brain!