The limbic system is a network of structures located beneath the cerebral cortex that is involved in the control of emotions, motivation and memory. This has been referred to as a fifth lobe. The term "you behaved like an animal" may have some relevance here in that the same structures found in the limbic system can be found in the brains of evolutionary ancient animals such as the alligator. In the alligator, the limbic system is heavily involved in smell, thereby playing an important role in defending territory, hunting and eating prey. In humans, the limbic system is less involved in smell and more involved in motivation and emotional behaviours.

One of the things that distinguishes the human brain from that of animals is the massive forebrain development in humans compared with animals. This has increased control over the functions of the limbic system. These functions include motivational behaviours such as obtaining food, drink and sex as well as organising emotional responses such as fear and anger. The limbic system can also be seen from an evolutionary perspective.

While the structures in this part of the brain interconnect, research has shown that the amygdala, a small almond shaped structure deep inside the brain as well as the hippocampus seem to be the main areas involved with emotions.

The amygdala is found deep within the antereo-inferior region of the temporal lobe. It connects with the hippocampus as well as the medial dorsal nucleus of the thalamus. These connections make it possible to play an important role in the mediation and control of major affective activities like friendship, love and affection, on the expression of mood, and especially on fear, rage and aggression.

One of the more significant studies in this area has come from Joseph LeDoux Ph. D. of New York University. His research has focused on the fear response. It shows that a portion of the amygdala known as the lateral nucleus appears to play a key role in fear conditioning. Follow this link for an easy to understand link to this structure.

These studies also show that the neural responses from a fear stimulus are also carried to the thalamus. This is a brain structure near the amygdala that acts as a channel for incoming sensory signals. From the thalamus, the nerve impulses (in this case from sound) are sent to the auditory portion of the sensory cortex, a region that carries out analysis of inputs and sends appropriate information to the amygdala. When nerve signals are received that indicate a threat, it sends out signals that trigger defensive behaviour, autonomic arousal including rapid heartbeat and raised blood pressure, hypoalgesia which is a diminished capacity to feel pain, a startle reflex reaction and the production of stress hormones. These physical changes are associated with the emotion of fear.

Another part of the amygdala, the central nucleus, is the portion responsible for sending out signals to trigger the fight or flight response.

The amygdala is fundamental for self preservation. When triggered, it gives rise to fear and anxiety which lead the animal into a stage of alertness, getting ready for fight or flight.

The hippocampus is particularly involved with memory, especially the formation of long-term memory.

The hypothalamus is believed to play a part with uncontrollable, loud laughing.

The hypothalamus is also believed to play a role in emotion. Its lateral parts seem to be involved with pleasure and rage while the median part is more likely to be involved with aversion, displeasure and a tendency to uncontrollable and loud laughing. The connections to the cortex in the temporal lobes are associated with thought and higher cognitive processes. They allow emotions to reach conscious awareness.

Hanging off the hypothalamus is the pituitary gland. The pituitary is an important part of the stress response because it acts with the hypothalamus to tell your adrenal glands to release stress hormones in response to life-threatening situations. These stress hormones flood your body so you have the energy to fight or flee. The hypothalamus and pituitary also release other hormones in response to stress, some of which can affect your emotions and contribute to feelings of anger or depression.