Overview of the Limbic System: Functions, Structures and Components

00:00 Welcome to this presentation on the limbic system. I think you’re going to find this to be a very fascinating system. This system is composed of various anatomic brain structures with multiple interconnections that serve to allow the species to survive, to reproduce. This system is also going to drive various behaviors. Let’s begin. Our first stop here is to consider the functional aspects of the limbic system. We’re seeing some of the components of the limbic system here in the illustration. We’ll dive into that detail here very, very shortly. One of the functional considerations is that the limbic system will drive various emotions. This can run from anger to pleasure, et cetera. As we'll see later in the presentation, the limbic system is also involved in memory. It helps us to maintain our attention to our surroundings and to our tasks. It drives our feeding behavior so that we have enough caloric intake to survive.

01:27 Then lastly, it also drives mating behavior to ensure the survival of the species. The components of the limbic lobe are interesting in where they’re located within the brain and the connections that they make. The limbic system is probably not a true anatomic lobe. But nonetheless, there is a classical definition of the anatomic components that do define the limbic lobe but there may be some variation from this classical definition. One of the first components to identify is shown here in green. This is the cingulate gyrus. This is on the medial aspect of each cerebral hemisphere and it resides just superior to the corpus callosum. Another component of the limbic system or the limbic lobe is in this area. This is the uncus and olfactory cortex. We’ll talk about the interconnectedness of this cortex with olfaction.

02:41 Another structure is the parahippocampal gyrus and the hippocampus. Those structures are located down in this area as well. We have the subcallosal gyrus shown in through here.

02:58 This lies just inferior to the corpus callosum that we see here. Lastly, we have for your consideration of anatomic components, septal nuclei. These are not shown in this particular illustration. However, we do have the amygdala, a very important anatomic component in the limbic lobe. Now, we’ll take a look at olfaction. This is very, very important within the limbic system. Odors are going to drive primal behavior. This is probably more of a consideration in other vertebrates. However, odors will drive even human behavior.

03:45 In order for this to function, there has to be an input. So odors are going to be inputted, if you will, into the primary olfactory cortex. That is the uncus. That area is shown right in through here. There’s also a direct input to the amygdala that is identified right in through here. The input to the amygdala will cause various emotions to drive appropriate behavior. If the odor is obnoxious, malodorous, it may cause the organism to move away from that particular odor. If it’s pleasurable, it will attract the individual.

04:35 There is also an indirect input to the hippocampus and this is essential in forming olfactory memory so that if we come across that odor again, we’ll have a memory of its impact on our emotional behavior. From the hippocampus, there is a connection to the hypothalamus. This is what will mediate our visceral responses to odors. The last connection here to consider is that to perceive odors, we’ll need to have input into the orbitofrontal cortex of the cerebrum. The hippocampus is another important anatomic component to the limbic lobe. The hippocampus is shown in through this area with the amygdala lying anterior to it. Functional considerations of the hippocampus are twofold. One is the hippocampus is essential in forming long-term memories of events. It’s also essential as we navigate especially in our environment. The hippocampus has a location in the floor of the horn of the lateral ventricle. So, the floor will be just kind of in this area of the hippocampus.

06:11 The input gate into the hippocampus is going to be through the dentate gyrus. That’s the main input of information. Other inputs are received by the hippocampus from the amygdala which lies here, the cingulate gyrus that was identified in an earlier slide. We also have an input from the prefrontal cortex of the cerebrum. The amygdala is our next structural component. Again, it is easy to identify in this illustration. We want to explore some of the functional considerations of this anatomic structure. Our first consideration is it will connect an emotional response to a certain stimulus. It’s important for you to realize that this response may be pleasurable or it may be somewhat revolting or even disgusting depending on the nature of the stimulus. This response then, this emotional response becomes imprinted in our memory. The amygdala is going to drive appropriate behavioral responses to inputs. This will include visceral, so maybe heart rate increases, maybe our respiratory rate increases. It also includes motor responses to inputs.

07:50 These motor responses may allow us to move toward the stimulus or may allow us to move away or drive us away from the stimulus, depending on the nature of that.