The amygdala is an almond shaped structure located deep within the brain’s medial temporal lobe. It is part of the limbic system and is thought to control our basest emotions, such as aggression, fear and arousal.
The amygdala is especially important for learning during classical conditioning when stimulus paired with the response is painful. For example, rats that have a shock paired with the presence of light have a larger startle response to a loud noise that is presented directly after a light is turned on. This is because the amygdala has learned that light is associated with pain, so while waiting for the shock, the rat is more aroused and has a larger startle response, a natural reaction, to a loud noise. In other words, the amygdala is important for learning what to fear.
Studies with fMRI scans have also supported this theory, as the amygdala shows lots of activity in response to fear and aggression, but not nearly so much as with sadness and happiness. When concerning fearful and angry expressions, the amygdala shows the most activation when shown a fearful face directed towards the viewer, and an angry face directed away from the viewer. Scientists believe that this is because of the confusion involved with these emotions. We expect someone to be fearful of their surrounding, but when that fear is directed at us, it is something we don’t understand unless put in a situation where we are trying to be frightening. It’s similar with the angry face as well. Anger is something that we sometimes expect to be directed at us, but when directed away from us, it’s more confusing and we desire to know what’s causing the anger.
Damage to the amygdala manifests itself in a “fearless” type of disposition. An individual with amygdala damage may report being afraid of snakes, but when confronted with one, they treat it like a domestic pet, even if venomous. In other words, they do not actually feel or experience the emotion of fear. However, another interesting discovery was made by examining amygdala damage was it’s role in recognizing fear. A normal human will focus on the eyes when asked to identify a person’s emotion. A person with amygdala damage will focus on the nose and mouth, and especially have problems identifying the emotions of fear and disgust. When asked to draw emotions, they are usually able to capture most emotional cues, even if they can’t identify them on a face, but when asked to draw fear, they are at a loss and cannot think of how to portray it on paper.
In summary: the amygdala plays an extremely important role in identifying emotion, and in expressing fear as well as aggression and arousal. Hopefully I’ll be able to link more studies about the amygdala soon!
The Medulla, Midbrain and Pons.
The brainstem is one of the oldest parts of the brainstem and is considered one of the “simplest” parts of the brain because creatures that are evolutionary older than humans possess brainstems that look like ours and also function like ours do. The brainstem controls basic autonomic actions (actions that don’t require conscious thought) that are essential for our survival like breathing, heart rate, blood pressure, digestion, alertness and arousal. Located at the juncture of the spinal chord and the cerebrum, it serves as a connections between the spinal chord and the rest of the brain, controlling the motor signals that travel between them. The brainstem is not a single brain structure, but also consists of the midbrain, the pons and the medulla.
The midbrain is located at the front of the brainstem and is involved in vision, hearing, and eye movement. Located in the back of the midbrain, a bundle of axons connect the cerebral cortex and are extremely important for voluntary motor functions.
The pons are involved in motor control and sensory analysis and are loacated towards the back of the brainstem. When the brain receives a sensory input, it travels through the pons before being redirected to the proper part of the cerebellum. They also are involved in functions such as posture, balance and sleep.
Finally, the Medulla, also called the Medulla Oblongata. This structure is located between the pons and the spinal chord, this is the structure that maintains the autonomic functions mentioned before, such as breathing and heart rate.