Where to start?

I think a good place to start is by touching your own hand. Really. Now realize that you didn't experience the sensation until the touch activated receptors in the skin, and those receptors sent information to the spinal cord, and the spinal cord sent the information to the brain.

The touch receptors are called somatosensory receptors, and they come in different types. Some are sensitive to gentle touch, others to strong touch, still others to pain -- including the pain you feel when you touch a hot stove. (The book discusses the different types of somatosensory receptors, but that's not key here.)

What's interesting to think about here is that you don't feel the touch sensation at the moment that something makes contact with your skin. Instead, the 'feeling' arises from brain activity. And so the brain needs to find out about the touch to your skin.

How does the touch information which begins at the somatosensory receptors in your skin get all the way to the brain? Neurons carry the information. And so understanding what neurons are, and how they carry 'information', becomes key to understanding any inner experience, including the experience of touch. We'll think about neurons a little later.

But before we get to neurons, let's briefly go through the key regions of the brain that you would encounter if you were to travel from the base of the brain (the brainstem), through the brain areas below the cortex (subcortical regions), in order to finally reach the outer layers of the brain, the cerebral cortex, where sensations of touch, hearing, and vision occur.

The Brainstem: Functions critical for life

The brainstem includes the medulla, pons, and midbrain - in that order as you climb above the spinal cord and ascend into the brain.

• The medulla and pons are critical to basic survival functions, including regulation of breathing, heart rate, and blood pressure. Of all brain injuries, severe damage to the medulla and pons are the most life-threatening.
• The midbrain is important in several aspects of behavior, but of particular interest here is the fact that most dopamine neurons originate (have their cell bodies in) the midbrain. As you may know, dopamine neurons play a key role in motivated behavior and addiction. The midbrain also contains two other key regions, the inferior and superior colliculi, described below.

To get a sense of the position of these brainstem structures, take a look here:


Notice the three brainstem areas labeled to the left. To the right, you'll see labels for the inferior colliculus and superior colliculus. Those are two regions of the midbrain that respond to sounds and sights, respectively. These midbrain areas only respond to events that are so obviously important (say a loud sound or the sudden appearance of a visual object near you) that they demand immediate attention - even before the cerebral cortex has had a chance to find out exactly what the auditory or visual event was.

On the bottom right, you'll also notice a large cabbage-shaped structure attached to the back of the pons called the cerebellum.

• The cerebellum plays a key role in movement coordination, movement precision, and the ability to learn skilled movements. Alchohol in large quantities may disrupt one's balance and skilled movements in large part because it impairs cerebellar function.

Try to answer questions 1-3 without looking at a brain image. If you haven't done this yet refresh the page and answer them again.

Subcortical Brain Regions: Motivation, emotion, memory and other functions

If you think of the brainstem as the basement of the brain and the cerebral cortex as the penthouse (we'll get to the cortex), there are a number of important brain structures between the two. For now, we'll consider just five of the most important ones: the hypothalamus, thalamus, hippocampus, amygdala, and basal ganglia.

• The hypothalamus is critical for hunger, thirst, sex drive, and other innate drive states.
• The thalamus receives information from the senses (vision, audition, etc) and passes it on to the cerebral cortex which, in turn, gives rise to the experience of seeing, hearing, etc. It is sometime referred to as a 'relay' station. For example, the neurons in the retina of the eye send visual information to an area of the thalamus that is dedicated to vision, and neurons originating in this thalamic nucleus relay the information to the visual cortex. When you wish to attend to a particular object in the environment, the cortex commands the thalamus to pass on more information about that object to the cortex. For instance, the cortex may decide that it wants to receive more information about the red object behind a bush, and commands the thalamus to send it more visual information about that object.
• The hippocampus plays a key role in memory. Individuals (and animals) who have suffered damage to the hippocampus are greatly impaired in storing and retrieving memories of events they've experienced.
• The amygdala is critical for learning about which environmental situations are dangerous. For instance, if you suffer a physical attack in a particular location, you will learn to be afraid when you pass by that location. Individuals (and animals) with amygdala damage fail to learn associations between environmental stimuli and aversive outcomes. A woman who suffered complete damage to the amygdala on both sides of her brain failed to acquire associations to dangerous stimuli, and showed virutally no signs of fear even in very dangerous situations.
• The basal ganglia are a group of brain structures that play an important role in allowing the behaviors that we frequently perform to become automatized habits. Since so much of our daily behavior involves acquired habits (using silverware, dialing the phone, getting dressed, etc., with little conscious attention required), a loss of basal ganglia function produces great difficulties in behavior. Usually, those with basal ganglia damage can still move, but movement becomes slow and extremely effortful.

Now take a look in Google to find images that include these brain regions. It's possible that you'll have to look at multiple images, for some brain illustrations will only show a subset of them. The idea is not to become a neuroanatomist today -- but to get a feel for where they lie with respect to one another.

Because these five areas are below the cortex, they are called "subcortical areas". when we talk of subcortical areas, we don't usually include the brainstem, even thoughit is below the cortex. When you feel comfortable with the descriptions of these subcortical areas, try the questions below. They're straightforward.

Review of material so far (brainstem and subcortical regions)

Bob received a gunshot wound to the , an area of the brain housing several brain regions, including the medulla, pons, and midbrain. The injury didn't affect all of these regions. Fortunately, there was no damage to the that sits just above the spinal cord. However, he did suffer damage to the where his dopamine cell bodies (the origin of the dopamine neurons) are located. It's likely he'll survive, but it's possible he'll have particular problems with . If the damage were to his hippocampus, it's likely he'd have had problems with .

brainstem, medulla, midbrain, motivation, memory