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  © 2008
  University of Idaho
  All rights reserved.
  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

So, let’s talk about the diencephalon and what it consists of.  As we see in slide three, the diencephalon consists of many structures. But there are two that are very, very important for us.  The first of these is the thalamus and the second of these is the hypothalamus.  As we can see in slide four, the thalamus is a relatively deep structure.  It’s surrounded by a variety of other structures and is extremely important for connecting and sending information back and forth to these structures.  So what is the thalamus?  Well the thalamus, as we can see in slide five, is basically a relay station.  It sends information from the sensory part of our system to the cortex and sends information from the cortex back to sensory and motor structures.  Essentially, the thalamus is a major center for collecting and integration of information, and has a major role in memory formation.  The best way to think about the thalamus is to think about O’Hare Airport, Minneapolis-St. Paul, Denver, or some of the other major airline hubs.  I live near Spokane, Washington.  When I fly to Washington, D. C., I get on my airplane and fly to Minneapolis-St. Paul.  I get off the airplane, then get on another airplane and fly to Washington, D. C.  When I want to fly back, I fly from Washington, D. C. back to Minneapolis-St. Paul, then, back to Spokane.  Minneapolis St. Paul, like other parts of the airline industry, is a hub where lots and lots of different planes come in, and then go to other locations.

The thalamus acts the same way.  It is a hub.  It gets information from a variety of different structures, collects and integrates that information, and then sends that information on to other structures.  Also, it has a major role in memory formation. 

Well, that’s the first part of the diencephalons.  What about the second part of the diencephalon?  That is the hypothalamus.  Well, the hypothalamus, as we see in slide six is part of what is called the Papez circuit or what is currently called the limbic system.  It receives information from a lot of different structures, is a lot smaller than the thalamus, and located in front of and below the thalamus (hypo meaning below).  The hypothalamus is also connected to the pituitary gland which secretes a lot of different hormones.  Its functions, as we see in slide seven, are numerous.  The hypothalamus is involved with things such as eating, drinking, fighting and sexual behavior.  It also regulates endocrine activity and is involved with emotion and helps control the autonomic nervous system.              Finally, the hypothalamus has been suggested to be involved with sexual identity.  That is, whether you become homosexual or not homosexual.  However, this is strongly debated in the literature and is very preliminary at this point.  In conclusion, the diencephalon (as we see in slide eight) is an older brain structure, but it is extremely, extremely important for normal functioning, and when you damage particular structures within it, the symptoms are pronounced.

Well now we’ve talked a little bit about the diencephalon, let’s move on and talk about the next major group of structures called the telencephalon.  This structure, as we see in slide nine, is the set of structures that is increased the most as evolution has progressed.  It has a wide variety of different particular structures.  You can see these structures in the diagram that I gave you in the earlier set of lectures a couple times ago.

The first major set of structures in the telencephalon is the olfactory system.  The olfactory system, as we see in slide 10, has a wide variety of different structures.  It also is not as well developed in humans as some other organisms such as dogs.  However, the olfactory system is extremely important in emotional arousal, especially pheronoms.  Of course, as we know just from the name, it’s involved with smell.

The second major set of structures that is involved with the telencephalon is what we call the limbic system.  Originally, this system was suggested by Papez, then it was added or modified by MacLean.  The limbic system has a wide variety of different roles and contains a variety of structures which we’ll talk about in a minute.  It’s highly involved with emotion, especially emotional memories, and is also involved with pleasure.  The limbic system, as we see in slide 12, has a wide variety of different structures and which you can see in slide 13.  So let’s talk about a few of these structures and kind of get an idea of what they are and what they do.

The first set of structures, as we see in slide 14, is what we called the cingulate gyrus.  The cingulated gyrus is also called the limbic cortex.  It basically borders older and newer evolutionary structures and basically is involved in emotional memories. 

The corpus callosum is another set of structures and is a neuron pathway.  What it does is connect the medial cortex of the left and right hemispheres.  So, what it’s doing is connecting the left and right sides of your brain.  There are many other structures that do that as well, but from the cortical side, this is the structure that primarily does that.

The next major structure, as we see in slide 16, is the septal area.  As we see, it’s primarily involved with controlling aggression and pleasure. 

In slide 17 we see another structure, called the amygdala.  The amygdala is highly involved with controlling rage behavior and aggression and is usually involved with connections and pathways to the septum.  The classic example of what can happen with the amygdala occurs when you damage it.  Let’s take a rat, a normal, docile rat and put it in a cage with a cat.  The rat becomes very afraid of the cat and runs and tries to get away from the cat, and the cat tries to do things that cats do.  So let’s take the rat out of the cage, put it in a stereotaxic instrument and destroy the amygdala, let the animal heal, and put the rat back in the cage with the cat.  In this case, the rat actually begins to attack the cat.  In fact, the rat will attack anything.  It seems that when you damage the amygdale it basically stops the controlling of the rage behavior that one has.  Consequently, the animal will attack anything that’s out there. 

The next major set of structures in the telencephalon is the hippocampal formation and the parahippocampal gyrus.  These two structures have extremely important roles in memory formation.  When you damage these structures, you cannot form any new memories.  You still have old memories, but you can’t form anything new.  So all you have are the memories you had before you damaged the structures.  This is very common damage that occurs with strokes.  It causes many major problems with the person who’s had a stroke then moved into or placed into a new facility.  That is, they always keep going back to their original place of residence.

Another major structure is the mammilary body of the hypothalamus.  The mammilary body is an extremely important structure within the limbic system and it’s involved with the regulation of emotional behavior.  It may also be involved with pleasure, pain and anger.  As we see at the very bottom of the page, it’s categorized in both the diencephalon and the telencephalon. So, in general, the limbic system primarily controls the animal instinctive behaviors that we have.  It’s involved with mating, it’s involved with feeding, flight and assorted other things that keep us alive and functioning normally. 

Well now that we’ve talked about the limbic system, let’s talk about another major group of structures within the telencephalon called the Basal Ganglia.  The basal ganglia, as we can see in slide 21, has a wide variety of different structures as well, so let’s talk about a few of these.  First of all, the basal ganglia, as we see in slide 22, is a set of structures that are just under the anterior aspects of the lateral ventricles and (as we see in slide 23) is involved with controlling movement.  However, while the cerebellum controls rapid movements, the basal ganglia helps us with controlling slower movements.  These include starting and stopping movements, balance, muscle contractions and relaxations that allow us to sit up straight, allow us to stand up straight without us falling over, etc.  In general, the basal ganglia controls the direction and amplitude of particular movements, especially postural movements. 

So, what happens when you damage this particular structure?  Well, when you damage basal ganglia structures, you get lots of problems in posture movements, walking, etc.  You also experience a lot of tremors, jerks, switchings, and so on.  These are classic symptoms that occur in a disease or disorder called Parkinson’s Syndrome.  The classic symptom of Parkinson’s Syndrome (which we’ll talk about a little bit later) is tremor at rest.  So, if you put your hand out straight it stays relatively constant, it doesn’t move too much.  A person with Parkinson’s will start to shake, and the more developed the Parkinson’s Syndrome is, the more shaking and the more tremor that the person will have.

Now, once you start to move, the tremor stops.  The reason  it stops is because you’re using other structures.  However, in later stages of the disease, you continue to have tremors all the time.  Generally this disorder occurs because the substantia nigra degenerates.  We’ll talk about this more detail when we talk about some particular disorders.  In the past, Parkinsonism was thought to be genetic and viral.  Today we know that it’s basically environmentally caused as well. 

So in conclusion, older cortical areas are involved in a wide variety of different activities and as we see in slide 27, they’re extremely, extremely important.  When you damage these structures, the symptoms are extremely involved and usually debilitating as well.

In the next section, we begin talking about newer evolutionary structures in the telencephalon and those primarily related to the cortex, so until then, we hope you have yourself a wonderful day.