Preliminaries: Brain Areas

Let’s talk about the areas of the brain and some of their functions.  I will start with a structural overview, and then dive into functionality.  If there is something that seems unfamiliar and isn’t bold, try reading this previous post.

The cerebrum, cerebellum, and brain stem make up the brain.  For our purposes, we will focus on the structural areas in the cerebrum.  The external part of the cerebrum  is the cerebral cortex (sometimes referred to as the cortex).  The cortex is the large, white part of the brain with grooves in Figure 1 (this is the part that most people think of when imagining the brain).  Some subcortical structures, not pictured in Figure 1, are directly below the cortex and are also considered a part of the cerebrum.  Subcortical simply means “below the cortex”, so the brain stem and cerebellum are subcortical structures, but are not part of the cerebrum.

MT.AP.Nervous.Cerebrum
Figure 1: Credit- http://www.therapycouch.com/AP.Nervous.Brain.htm

Structurally, the left and right hemispheres of the cerebral cortex, (recall that this division is made by the midsagittal plane), are identical.  There are four large structural divisions in the cerebral cortex: the frontal, parietal, occipital, and temporal lobes, and each hemisphere contains part of the lobe.  For example, the temporal lobe in the left hemisphere is referred to as the left temporal lobe.  Below is an image of these divisions.

brainstructure
Figure 2: Credit- http://controlmind.info/human-brain/structure-of-the-brain

Sulci and gyri are further descriptors of the cortex.  In Figure 2, we can see that the cortex has grooves and folds.  The grooves (sulci, sing. sulcus) are the lines, and the folds (gyri, sing. gyrus) are the spaces in between them.  We can see that a few major sulci are the borders of the lobes.  For example, the central sulcus is the groove between the frontal and parietal lobes.

Using the directions described in the previous post, we can refer to specific gyri and sulci, such as the left inferior temporal gyrus.  Can you point it out in Figure 2? Similarly, there is the left superior temporal gyrus and the left middle temporal gyrus.  Refer to Figure 3 below for more terms!  Don’t worry if these are difficult to remember.  Understanding the basic directions, the four lobes, and the difference between sulci and gyri will be enough context for a majority of the papers I post about.

great-of-sulci-and-gyri-brain
Figure 3: Important sulci and gyri

The subcortical structures include the limbic system (hosting the hippocampus and amygdala), the basal ganglia, and the olfactory bulb.  See Figure 4 below.  All of the labeled areas besides the brain stem and cerebellum are part of the cerebrum.

3_Limbic_System_03
Figure 4: Subcortical structures.  Found at sott.net, copyright unknown.

Now that I have covered the major structures of the brain, I’ll dive into the functionality of some of these regions.

Brain stem:  The brain stem is a continuation of the spinal cord.  It controls the most basic functions in the body, such as heart rate, balance, reflexes, breathing, and consciousness.  It can also be thought of as the information transporter, as signals from other parts of the brain travel down the brain stem to the rest of the body, and vice versa.

As we go through this, you may find a general principle emerging: superior areas of the brain deal with evolutionarily complex functions, while inferior areas control basic functions.  This isn’t a rule, but a trend, and applies to the brain as a whole (cerebrum vs. brain stem and cerebellum) as well as areas within the cerebrum.

Cerebellum:  This area is involved in motor control and motor learning.  By receiving inputs from multiple areas and coordinating the these signals, the cerebellum mediates posture, balance, and motor precision.

Cerebrum:  As a whole, the cerebrum controls language, vision, spatial perception, fear response, hearing, emotions, and many other things.  It is where our higher-level functioning and personalities develop from.

  • hippocampus: instrumental for forming long-term memories
  • amygdala: primarily associated with eliciting emotional responses (fear, anxiety, reward)
  • basal ganglia: aids fluidity of movement
  • olfactory bulb: transfers smell information from the nose to the rest of the cerebrum
  • temporal lobe:  mainly processes sound, and is involved in listening and hearing.  It is also involved in language comprehension and visual object recognition.  Some specific areas within the temporal lobe are listed below.
    •  Wernicke’s area: located in the posterior portion of the left superior temporal gyrus.  It’s main function is to aid in comprehension of language.  Damage to this area has show that patients can create grammatically correct sentences, but there is no discernible meaning from them.
    • primary auditory cortex: located bilaterally (on both the left and right hemispheres of the brain) in the superior temporal gyrus.  As the name suggests, it is related to tasks in hearing, such as recognizing the location sounds are coming from.
  • occipital lobe:  the occipital lobe is the main visual processing center of the brain. Neurons (cells of the nervous system) in the primary visual cortex receive visual input from the eyes (by way of the thalamus, a subcortical structure, see Figure 4).  From here, the signal is sent to be further processed in other areas.
  • parietal lobe: this area is very important for integrating the sensory inputs from other areas of the brain and body.  For example, the parietal lobe is essential for having spatial awareness.  This isn’t a direct result of visual processing, but also requires integrated information about position of the limbs and body with respect to the environment.
    • primary somatosensory cortex: this is located in the postcentral gyrus (see Figure 3).  It contains a “map” of the body, with sensation of touch triggering activation in corresponding areas of the primary somatosensory cortex, or vice-versa.
  • frontal lobe:  the frontal lobe is where a lot of our emotional and social abilities, such as conscience, are developed.  Voluntary movement is also controlled by the frontal lobe.
    • primary motor cortex: located in the precentral gyrus (see Figure 3).  Similarly to the primary somatosensory cortex, it has a map of the body, but neuronal activation is triggered when muscles in the corresponding body parts are in use.

Alright, this is it for now.  Hopefully now you have a better idea of the divisions in the brain and some overall functionality.  Stay tuned for the next post about imaging techniques!

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