Last week I wrote in brief about the differences between conscious and non-conscious thought, and how experiments show humans use both. Even the most primitive animal brain is an extremely complicated organ, and the human brain is obviously the most advanced brain we've encountered. Conceptually there are three main sections of the human brain, corresponding to the evolutionary processes that produced the brain.
Pardon the aside, but I wanted to say a word to the Christian readers who believe in Intelligent Design instead of evolution. Feel free to interpret "evolution" with "how God chose to create life". Your personal belief about how humans came to exist won't change your interpretation of what I have to say, so don't let my choice of language get in the way. Remember, I was a Christian for 30 years. I was taught creationism by my parents. In high school I believed the theory of evolution, and just said "God used evolution to create humans". Now I just think "humans were created through evolution". I still think people who believe in Intelligent Design are wrong given the data, but I see no reason to be condescending or judgmental about it.
As I was saying, there are three main sections of the brain. At the core is the so called "Reptilian Brain", or more formally the brain stem. This section handles basic reflexive responses such as "fight or flight", mating instincts, and the fear of other species. It also handles exactly one emotion: rage. Next is the Mammalian Brain, or Limbic system. This is the area of the brain that handles all other emotions, as well as concepts like family, culture, and attachments. Some aspects of conscious thought and self-identity are handled by the mammalian brain as well. Last is the Neo-cortex, which is responsible for higher level thought such as speech, reasoning, imagination, and speculation.
While there's a clear physical boundary between the reptilian and mammalian brains, the division between mammalian (limbic) and neo-cortex is not as clear, and there seems to be a stronger bleed between the functions. For example, some conscious thoughts are handled by the mammalian brain while others are handled by the neo-cortex.
Humans have all three brain sections, as do higher mammals such as other primates and larger mammals. Small primates such as rodents do not have a neo-cortex, although they do have the limbic system and reptilian brain. And as the name implies, all reptiles have the reptilian brain, but lack the mammalian brain and neo-cortex. So the brain sections correspond to different evolutionary forks. The primary feature that separates mammals from reptiles is not hair or internal gestation, but a more advanced brain.
If that's true, then reptiles don't actually have conscious thought. They simply respond to stimuli in the same fashion every time. But mammals, having a memory, can learn from past experiences and modify their behavior. Perhaps this is how mammals survived the dinosaurs after a natural disaster hit the earth. Dinosaur brains weren't programmed to handle the "meteor crashed into the earth and all your normal food dies" situation, whereas mammals could learn to find new food sources.
In computer science terms, the reptilian brain is analogous to a state machine, or a simple circuit board. It's pure hardware, and if you give it the same set of inputs, it produces the same set of outputs every time. It has no memory. The mammalian brain is more like a simple computer program, in that its responses are based both on sensory input and on past memories and experiences. Running the same computer program multiple times might produce different results. Mammals have the ability to learn throughout their life while reptiles do not. And since the neo-cortex handles imagination, reasoning, and "what if?" scenarios, it's closer in function to an operating system. An OS can run multiple programs in parallel, similar to the neo-cortex's ability to think about multiple thoughts at the same time, even conflicting thoughts.
This biological framework provides an interesting context from which to answer the questions "What are emotions?" and "Can a computer have emotions?" Some day I'll write on that, but there's a lot more to say than should be stuffed at the end of this column. In the meantime you'll just have to speculate.