AssessmentsAnatomy of the limbic system
USMLE® Step 1 style questions USMLE
A 47-year-old woman sustains a brain injury after a motor vehicle accident. The patient cannot form memories of events taking place after the accident, including her hospital stay and subsequent time spent recovering at home. However, she can recall events that occurred before the accident.
Which of the following brain structures was most likely injured in this patient?
Content Reviewers:Viviana Popa, MD
Memory formation and the recollection of those memories are supported by the limbic system, and It can even influence responses of the autonomic nervous system, like cardiovascular or gastrointestinal functions.
To easily recall some of the functions, you can remember the famous 5 F’s, which are: Feeding, Fleeing, Fighting, Feeling and...Fornicating, the last one being, really, just a fancy word for Sex.
Structures that are included in the limbic system include the: hypothalamus, olfactory cortex, hippocampal formation, amygdala, subcallosal area, cingulate gyrus, parahippocampal gyrus, mammillary bodies and the basal forebrain.
Let’s take a closer look at each of them, starting with the hippocampal formation, which is crucial for converting short-term memory into long-term memory, shipping those memories into other cortical regions for long-term storage and assisting in retrieval of memories when needed.
It is also involved in spatial orientation, which is the ability to identify the position of our body relative to the objects around us.
On a transverse section of the temporal lobe, we can see the hippocampal formation forming the floor of the inferior horn of the lateral ventricle. But, the best plane for the visualisation of this structure is actually the coronal plane.
The hippocampus is involved in long-term memory formation and helps decide what should be stored within the cerebral cortex as a memory.
The next three structures that belong to the limbic system are the subcallosal area, the cingulate gyrus and the parahippocampal gyrus. These structures influence emotional reactions and support learning and memory formation.
On a mid-sagittal section of the brain, we can see the subcallosal area on the medial side of the frontal lobe, just anterior to the lamina terminalis and inferior to the rostrum of the corpus callosum.
On the ventral and medial aspect of the temporal lobe, spreading anteriorly from the splenium of the corpus callosum, we see the parahippocampal gyrus, which is separated from the rest of the temporal lobe by the collateral sulcus.
Similarly, in the mid-sagittal plane of the brain, they can be seen posterior to the tuber cinereum and anterior to the tegmentum of the midbrain. In the coronal plane, we can see the mammillary bodies inferior to the third ventricle.
Now, all of the hypothalamic nuclei are part of the limbic system, as “homeostasis” is one of their major functions, but the mammillary bodies are especially important as they play a role in learning and memory and are connected to the hippocampus.
These structures assist in episodic memory, which is the ability to recall specific situations, or episodes, from our lives, like the place and time of our first kiss and the emotional reaction associated with it.
Great! Now let’s take a closer look at the amygdala, which means “almond” in latin. The amygdala contains numerous nuclei and is connected with various parts of the nervous system, but the important connections with other limbic system structures include the hypothalamus, olfactory cortex, hippocampal formation, frontal lobe and the sensory association cortices.
Because of this, the amygdala is involved in emotional responses, especially fear, rage and aggression, modulation of memory and influences attention and decision making.
Let’s take a short break and see if you can recall the role of the hippocampal formation!
Ok, now that we saw the primary structures that make up the limbic system, let’s go through just a few more structures that are connected to and work together with it.