© 2010
  University of Idaho
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  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

First, as you look at the cortex, it’s the most developed tissue in humans.  It has lots and lots of folds and fissures.  The folds of the tissue that we have on the brain are what we call Gyri and we call a gyrus one single piece of tissue.  The fissures or valleys in the cortex that we see or the spaces between these folds of tissue are what are called sulci or a sulcus.  This is what you see from the outside of the brain.  Ultimately, these folds and fissures allows more surface area for more neurons to be loaded.  As a result, you have a lot more neurons for your body size than all other organisms out there.  This gives you a distinct evolutionary advantage.

When you look at gyri and all of the different cortical structures related to the cortex, note that each one of these structures has a particular name.  We need to know those names because they provide anatomical landmarks for us when we’re trying to do surgery or other types of things.  Now, one of the things that you’ll notice as you look at the first picture in DeArmond et al. is that the cortex and the lobes are divided into several different sections, and as we can see in slide three, each lobe has a specific function.  So, let’s talk a little bit about how the nervous system and the cortex are divided, and what gives us some different anatomical landmarks. 

First of all, the cortex is separated in the middle of the brain by a fissure called the central fissure.  It in essence splits the brain into left and right halves, or what we call left and right hemispheres.  As we see in slide four, the hemispheres have different functions.  First of all, the left hemisphere controls the right side of the body and the right hemisphere controls the left side of the body.  These fibers from each hemisphere cross over a particular point in the hindbrain and midbrain structures called the pyramidal descussation.  This hemispheric specialization also occurs for other things as well.  We see this on slide five.  That is, the left hemisphere tends to be more for serial tasks or things that occur one after another.  Classic examples of those things are reading, writing, or verbal behavior.  The right hemisphere is more specialized in controlling specific elements; that is, visual-spatial activities.  We can break this out and do experiments to see if there are different roles and functions for each of these hemispheres.  However, for us normally, the system works together.  It works together because the corpus callosum connects both sides.  As a result, we are able to function relatively well and it seems almost effortless.

Now there’s a variety of different landmarks that go on within each hemisphere and these landmarks help to separate the lobes.  Each of these lobes have different functions.  As we see here on slide six, there are three different fissures or different sulci that are extremely important for us.  They set up anatomical landmarks and what we call the particular lobes of the brain.

The first one of these landmarks is called the central sulcus.  It separates the frontal and the parietal lobes.  You can see this in a nice picture in DeArmond et al. and other pictures in Carlson as well.  The second sulcus that we have is the lateral sulcus.  The lateral sulcus separates the temporal lobe from the frontal and parietal lobes.  Finally we have the parietal occipital sulcus.  The parietal occipital sulcus separates the parietal lobe from the occipital lobe. However, this landmark isn’t visible on the outside of the brain; it is on the inside of the brain. So, the sulcus is actually on the medial side rather than the lateral or outside part of the brain.  Now, as we see here in slide seven, because of using these different sulci we have identified four distinct lobes of the brain; that is the frontal, the parietal, temporal and occipital lobes.  So let’s talk about each of these lobes and kind of what they do. 

The first of these lobes is shown in slide eight and is the frontal lobe.  The frontal lobe contains what is called the precentral gyrus.  The precentral gyrus is what we call your primary motor cortex and you can see a copy of this on slide nine.  In essence, the precentral gyrus is the structure that is in kind of a lavender color.  The precentral gyrus is also called Broadman’s area four.  It, like all other parts of telencephalon areas are located at the bottom of the lesson three topic sheet.  You can click on them to see where all the other areas are.  The precentral gyrus area, again, is responsible primarily for voluntary motor movement.  In addition to area four, we also have two other areas that are important.  These are part of the premotor cortex. Two of these structures are the superior frontal gyrus and middle frontal gyrus.  In essence, the premotor cortex is responsible for setting muscle tone and getting area four to work correctly.  As you can see in slide nine, these structures are located in front of the precentral gyrus.  If you look in the DeArmond book, you can see where the superior frontal gyrus and middle frontal gyrus’ are located.  So what do we do to get movement?  Well as we see in slide 10, the first thing is the premotor areas must prepare the muscles to contract, then area four causes the muscles to begin to contract, and the basal ganglia, cerebellum, and other brain structures help to smooth out the movement.  So, we get a very nice, smooth contraction of a particular muscle. 

Now there’s a couple of areas in the motor strip that are extremely important.  The first of these is called Broca’s area. Broca’s area is located at the bottom of area four, six and eight.   It is primarily concerned with speech.  When you damage Broca’s area, the person can understand speech but they cannot talk well.  The reason they cannot talk well is because they have damaged some part of a voluntary motor strip.  This damage is called Broca’s aphasia.  To get an idea about Broca’s aphasia, put your tongue on one side of your mouth, bite down (but not too hard) with your teeth so you hold the tongue in place.  Then talk only with the other side of the mouth (sounds).  Now it may be somewhat understandable, depending on how bad the damage is, but it is not normal speech that you would have.  Sometimes with good speech therapy, one can retrain oneself to speak a relatively normally but it usually isn’t as good as what you were doing before you had the damage.

The remainder of the frontal lobe is what we call association cortex or association area. This association area is extremely important for thought processes, memory formation, and problem solving.  When you go and damage each of these structures, or any structures within the frontal lobe, you often have problems with memory and recall.  It just depends on the kind of memories and recall that you’re trying to do.

So that’s the frontal lobe.  What about some other structures that we have within the brain.  The next major set of structures is called the parietal lobe.  The parietal lobe also contains a variety of different sets of structures.  The first of these structures is area three.  Area three is located within the postcentral gyrus and is part of what we call the somatosensory cortex.  If you look at the picture again, you can kind of see where the somatosensory cortex is.  The somatosensory cortex is basically concerned with sensory function.  That is, where you feel pain, where you feel temperature, and on and on.  In addition to area three, there’s two other areas and association cortex that’s located within the parietal lobe.  Each of these basically help to interpret what is going on within area three.  So, as you can see here, you have your postcentral gyrus which includes a lot of the different structures, and the remainder within the lobe is basically associated with understanding what is going on within area three.

The next structure I want to talk about is the temporal lobe.  The temporal lobe is located below the lateral sulcus and basically it’s concerned with hearing and patterning of sound.  That is the concept of what we call speech.  It also contains another major structure and that is what is called Wernicke’s area.  Wernicke’s area is basically a sub-area of the left temporal lobe and as we can see in slide 16, it’s primarily concerned with the integration and comprehension of speech.  Wernicke’s area also receives a large amount of information from other areas, such as the occipital lobe.  When you damage Wernicke’s area, you can speak fluently but the content is nonsense.  This is called Wernicke’s aphasia.  We will talk more about Wernicke’s aphasia when we talk about disorders.

In addition, it’s not only difficult to speak and talk well, but it’s also hard to comprehend and understand other stimuli.  Some classic stimuli that we don’t understand is from reading.  When you read you kind of put things into kind of an auditory processing mode and put it into your brain.  If Wernicke’s area is not working well, that does not happen.

Now, a related area that is a pathway directly between Wernicke’s and Broca’s areas is a structure called the Arcuate Fasiculus.  The arcuate fasiculus is basically a pathway and all it basically does is connect Wernicke’s area with Broca’s area.  When you damage this area with a stroke or with some kind of trauma, the symptoms look very, very similar to Wernicke’s aphasia. 

Well now we’ve talked about the frontal, the parietal and temporal lobe, let’s talk about the last lobe that is called the occipital lobe.  The occipital lobe is primarily concerned with vision. Like other areas, it also has Broadman’s areas as well, and the most important one of these is called Broadman’s area 17.  Broadman’s area 17 is called your primary visual cortex. When you damage this structure, you in essence go blind.  Ultimately, this is where the visual information goes first in your cortex before it goes to other structures.

Now in addition to area 17, there’s a couple of other areas (areas 18 and 19).  These are what we call the visual association cortex.  It helps with the organization of the visual stimuli that we have out there.  So, when you damage these structures, you may be able to see that there’s something out there (because you haven’t damaged the primary visual cortex), but you can’t recognize what the particular stimuli are.  Now, once the stimuli have been recognized, the information is then sent on to other lobes (such as temporal lobe) where you then identify what those things are, and you put some kind of graphical or auditory context to it.

The last area that I’m going to include here is not really a lobe.  It is sometimes in some books called the lobe and in other books is not.  This structure is called the Island of Rile.  The Island of Rile is also called the Insular Lobe and it’s located underneath the lateral sulcus and primarily it is concerned with olfaction, memory, and other types of things.

So, in general and conclusion, the cortex has lots and lots of different structures and each of these structures have lots and lots of functions.  The key about the brain and the cortex is that it’s very resistant to damage.  However, when you do damage it, you can have lots and lots of problems.  And as we have seen in the neuropsychological test batteries, the problems can identify where the particular brain is damaged.

In the next section, we will begin talking about some specific brain structures and what they do.  But until that time, I want you to study hard, review all the brain structures again in the cortex and other things in DeArmond et al.