Diseases of the Brain

Steven Lewis, University of New Mexico, College of Medicine
 

Everything you experience depends on the functions of your brain. This includes obvious things like vision, movement, and conscious decision making. People are generally aware of when these mental activities occur, and are comfortable thinking that their brain controls these activities. However, less obvious functions, like motivation, will-power, humor, love, pleasure, and sadness, these also all depend on the functions of the brain. It’s sometimes harder for people to accept that the parts of behavior that just seem to be part of who you are depend on an organ of the body.
 
We know that brain function is tied to everything we think and feel because, unfortunately, people get their brains injured all the time. Following significant head injuries there are frequently changes in the way people think and behave. Further, in those cases when we can figure out what part of the brain was injured, and we see how someone’s behavior changes, we can start to attribute a brain function to that injured part of the brain. So, for example, because people who had injuries to the occipital lobe at the back of the brain had disrupted vision or blindness, we learned that the occipital lobe has a role in visual perception. There are similar examples for injuries that predictably lead to problems in speech, or problems in complex reasoning, and from these patterns of injuries and lost function we discovered areas of the brain necessary for speech and complex reasoning. But what about more complicated functions – things like wanting to socialize with other people or keeping your mood up – are these products of brain function?
 
There are people who experience changes in mood or socializing after brain injuries, but the patterns aren’t as reliable as with injuries that affect speech or vision. This has been a clue that complicated behaviors—like how your mood reacts to stress; getting happy, depressed, or frightened around other people; or how good you are at focusing when the rewards for your work are far in the future—are associated with patterns of brain activity spread over larger areas of the brain. At one time, we weren’t sure we’d ever be able to make sense of these large and complicated patterns of brain activity. But over the last 25 years we’ve developed tools that have helped us start to understand what goes wrong in people’s brains, leading to mental illness.
 
If we’re looking for the relationship between brain function and behavior, we need to have really precise descriptions of how people feel and behave. Our best descriptions of behaviors are often descriptions of mental illness, in the form of rating scales. The creation of precise and valid rating scales has given us the information we need to relate changes in brain function to changes in behavior.
 
This presentation will start with an overall description of the brain, focusing primarily on the cortex, because that’s where most brain activity is found. We’ll focus a little more on the parts of the brain that tend to get ignored because their functions are broader and harder to describe in short outlines. We’ll then review some particular mental illnesses, and show how they are different from the moods and feelings we all share. Finally, we’ll see how brain activity in most people is different from brain activity in people who are experiencing mental illnesses.
 

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