Healthy Brain, Happy Life (3 page)

THE BRAIN AND ALL ITS PARTS

Neuroscientists used to think of the different parts of the brain as housing certain functions. We know now that that’s only partially true. While specific areas of the brain do have specific functions (see the following list), it’s important to keep in mind that all parts of the brain are connected, like a vast and intricate network.

(Courtesy of Ashley Halsey)

•  
Frontal lobe:
This front section of the brain houses the all-important prefrontal cortex (making up the front part of the frontal lobe), understood to be the so-called seat of personality and integral to planning and attention, working memory, decision making, and managing social behavior. The primary motor cortex, the area responsible for allowing us to move our bodies, forms the most posterior (toward the back) boundary of the frontal lobe.

•  
Parietal lobe:
This lobe is important for visual–spatial functions and works with the frontal lobe to help make decisions. The part of the cortex responsible for allowing us to feel sensations from our bodies (known as the primary touch cortex) is located at the most anterior (toward the front) part of the parietal lobe.

•  
Occipital lobe:
This is the part of the brain that allows us to see.

•  
Temporal lobe:
This is the part of the brain involved in hearing, vision, and memory.

•  
Hippocampus:
Located deep inside the temporal lobe, this area is crucial for the formation of long-term memories; it’s also involved in aspects of mood and imagination.

•  
Amygdala:
This structure, which is critical for the processing of and response to emotions such as fear, anger, and attraction, is also located deep inside the temporal lobe right in front of the hippocampus.

•  
Striatum:
This area, which is seen best from a cut down the middle of the brain, is involved in motor function and plays an important role in how we form habits (and why they are so hard to break!); it’s also integral to the reward system and how addictions develop.

Like the best teachers do, Diamond then made what initially seemed incomprehensibly complex totally understandable. She told us that this big complex mass of tissue was really made up of only two kinds of cells: neurons and glia. Neurons are the workhorses of the brain and each contains a cell body, which is the control center of the neuron; input structures called dendrites, which look like big tree branches, that receive information coming into the cell body; and a thin output structure called the axon, which can also have lots of branches.

What makes neurons unique from any other cell in the body is that they are able to communicate via brief bursts of electrical activity, called action potentials, or spikes. That cross talk between the axon of one neuron and the dendrite of the next one takes place at a special communication point between the two called a synapse. It’s the brain’s electrical “chatter,” or axon-to-dendrite communication, that is the basis for all the brain does.

Neurons and their connections.

(Courtesy of Ashley Halsey)

What about the glia cells?
Glia
means “glue,” and the cells were so named because scientists in the nineteenth century mistakenly thought these cells had something to do with holding the brain together. While it’s true that some of the glia cells do serve a scaffolding function in the brain, we now know that they actually serve a wide range of different support functions for neurons. Glia cells supply nutrients and oxygen to the neurons; they form a special coating on the neurons called myelin, which is required for normal synaptic transmission; and they attack germs and serve as the brain’s cleanup crew, removing the debris from dead neurons. Exciting new evidence suggests that glia cells may even be playing an important role in certain cognitive functions including memory. Many believe there are ten to fifty times more glia in the brain than neurons, but this often-repeated statistic is being challenged by new studies suggesting that the ratio is closer to one to one.

Diamond then explained that if we had a big bucket of neurons and another big bucket of glia, we, at least in theory, would be able to build a brain. But the big puzzle is figuring out exactly how we put those neurons and glia together to work as beautifully and elegantly—as perfectly and imperfectly, as correctly and incorrectly—as a real brain. I learned that day that figuring out those connections and the general question of how a brain is put together, otherwise known as the study of neuroanatomy, was Diamond’s specialty.

But what truly captivated the nascent scientist in me that first day of class was her description of brain plasticity. This does not mean your brain is made of plastic, but rather it refers to the idea that the brain has an essential ability to change (like a piece of malleable plastic) as a result of experience. And by
change
she meant the brain could grow new connections within itself. I still remember her giving us the analogy that if you study really hard your brain may ache because of all the axons and dendrites growing and straining to make new connections.

In fact, Diamond (as one of the very few women in science at the time) had been responsible for the now classic research starting in the early 1960s on exactly how plastic, or malleable, our brains really are. At that time, it was known that brains could change and grow extensively from infancy to adulthood, but it was believed that once we hit adulthood, our brains were set in stone, with no ability to grow or change.

Diamond and her colleagues at Berkeley challenged this notion in a very big way. In their now famous study, they asked what would happen to the brains of adult rats if you housed them in what she called “enriched environments.” This meant letting them live in a sort of Disney World for rodents, with lots of colorful toys to play with, lots of space to run around in, and lots of other rats to engage with. The researchers were looking to topple the idea that the adult human brain was fixed—that is, that it was not capable of change. In order to answer their question, Diamond and her team changed the physical environment that the rats lived in and asked whether there was any effect on the physical structure of the brain. If there was evidence of change in the rats, then that meant under certain conditions, human brains might also be able to grow, adapt, or change.

What were the results of housing rats in Disney World? Compared to rats living in what the researchers called impoverished environments, with no toys and only a few other rats to play with, the rats living in Disney World actually had brains that were physically
larger
than the impoverished rats. Diamond showed that in the enriched environment, dendritic branches (those input structures of the neurons that look like tree branches) actually
grow
and
expand,
allowing the cells to receive and process larger amounts of information. In fact, she showed that not only were there more dendritic branches but more synaptic connections, more blood vessels in the brain (that means better access to oxygen and nutrients), and higher levels of good brain chemicals like the neurotransmitter acetylcholine and particular growth factors.

Diamond explained that these differences in brain size were a direct reflection of the nature of the rats’ environments. In other words, the size and function of a brain—rat or human—is highly sensitive and reactive to all aspects of any given environment—physical, psychological, emotional, and cognitive. This constant interaction between the brain and the environment, combined with the brain’s ability to respond by changing its anatomical structure and physiology, is what neuroscientists mean by the term
brain plasticity.
Stimulate the brain with new things to do or new individuals to interact with and it reacts by creating
new connections
that cause it to actually
expand in size.
But deprive your brain of new stimulation or bore it with doing the same thing day after day after day, and the connections will
wither away
and your brain will actually
shrink.

In other words, your brain is constantly responding to the way you interact with the world. The more diverse and complicated your interactions, the more neural connections your brain will make. The less enriched your environment and experience, the fewer neural connections your brain will make. There was nothing particularly special about the rats raised in Disney World; in fact all the rats in the study had the same capacity for reaction to stimuli. Do you play the piano? Then the part of your brain that represents the motor functions of your hands has changed relative to people who don’t play the piano. Do you paint? Play tennis? Bowl? All of these things we also know change your brain. We now understand that even the everyday things that we learn—the name of the guy that takes our order at Starbucks or the name of the newest movie we want to see—are all examples of the brain learning, which in turn causes the brain to make micro changes in its structure.

It was almost too much fascinating information to take in for the first day of class. But one thing was for sure. The first day of “The Brain and Its Potential” class changed my life. I walked in a curious enthusiastic freshman wanting to soak it all in, and I walked out a curious enthusiastic freshman with newfound purpose and meaning. I knew after that day in class what I wanted to do with my life. I wanted to study that lumpy mass of tissue and discover some of the secrets to understanding what it is to be human. I wanted to be a neuroscientist.

Over the next four
years, I took many more classes with Diamond, including her wildly popular gross human anatomy class and her more advanced neuroanatomy class. You might not realize how much passion, enthusiasm, and clarity (plus a little magic) it takes to make an anatomy class really interesting. A course in gross human anatomy is a practice of committing to memory every single detail of your body—from your bones to your muscles (including the specific locations where bones attach) as well as every single internal organ and how each of them is hooked up to another. There are more than seventy-five hundred parts to the human body! As you can imagine, memorizing every single one is an enormous task. If a professor simply presented all this anatomical information in a flat, listlike way, the class would be akin to reading this year’s new income tax regulations—dry as dirt. But Diamond revealed the human body to us as if we were on a grand adventure in an exciting new universe, both familiar and strange. She also made everything personal, telling us that learning about the anatomy of our bodies was going to teach us about who we were as people. If we were going to keep our anatomy and our brain for the rest of our lives, wouldn’t it make sense to know what we were working with?

Diamond was a master at mixing information about the origin of an anatomical term or some lesser known anatomical fact with more basic lessons, therefore making every last piece of information seem relevant.

For example, she asked us: