The limbic system is one of the most essential systems in the human body for it is made up of the structures that perform the most vital activities in the body that are required for one to survive. It lies near the thalamus just on its sides, and under the cerebrum.
When being categorized using the brain is said to contain the structures that make up the forebrain. The major part of the brain region that scientifically are proven that they make up the limbic system they included the hypothalamus, the amygdala, limbic cortex, and the hippocampal formation. Moreover, the cingulate gyrus, olfactory cortex, and the fornix are considered to be of the limbic system.
The limbic system is involved in memory and emotion through the Amygdala structure, which is almond shaped and contains a huge mass of the nuclei, moreover, it is found deep inside the temporal lobes just the medial region of the hypothalamus, adjacent hippocampus structure. Its main functions include hormonal secretions, response to various emotions, regulation of the autonomic responses which are related to fear and finally responds to arousals. Therefore, from the studies, it is true to say that the fear network, especially in animals, is controlled in the amygdala whereby it projects to the hypothalamus and fined projected to the brainstem. Thus, giving the reason why fear responses are observed in some reactions.
What is the limbic system?
It receives its name from the Latin root word limbus, which means “rim” in referral to the curved rim of the cortex which includes the cingulate and the parahippocampal (near the hippocampus) gyri. The limbic system is mainly composed of the hippocampus, amygdala, thalamus and hypothalamus. The limbic system also referred to as the emotional brain
The hippocampus has been known to secure memories as it plays a role in memory formation and recalling of memories. Hippocampus also plays a part in dream-formation where figments of our memories are pieced together in a random order to form a meaning. Studies have shown that people who suffer from depression have a shrunken hippocampus. This can be explained on the basis of the atrophy of the hippocampus. The constant stress takes a toll on the neurons and leads to retraction of dendritic processes in hippocampal neurons, inhibition of neurogenesis (formation of neurons) in the adult hippocampus, and loss of pre-existing hippocampal neurons (i.e., neurotoxicity). In addition to this, a hormonal theory also exists. You see, when the body is in stress, the body releases stress hormones, out of which, one is cortisol. These stress hormones increase the glucose levels in the blood to the body is ready in case of danger. Constant stress means constantly higher levels of cortisol. This also damages the hippocampus.
Furthermore, studies have also shown that post-traumatic stress disorder (PTSD) is associated with a smaller hippocampus.
The thalamus, meaning “chamber" in Greek, is a large mass of grey matter in the brain. It performs various tasks such as relaying of sensory signals, including motor signals to the cerebral cortex, and the regulation of consciousness, sleep, and alertness.
It relays various sensory signals all the way to the cerebral cortex and gives us motor control ability. Further, it receives the auditory, the somatosensory and the visual sensory signals, therefore the thalamus has the ability to modify and integrate various information that passes through it. As such, nearly all sensory information from the environment usually passes through the thalamus. For example, taking the visual information in the body it first moves from the eye the all the way to the optic nerve and tract than to the thalamus and finally passed to the visual cortex where perception is created. However, the olfactory information is the only one that is not perceived in the thalamus and has direct cortical projections. This explains why smells can be so powerfully evocative of memory and emotional experience.
The hypothalamus is the region present below the thalamus and is responsible for controlling and regulating various bodily functions such as heart rate, body temperature, et cetera. Coupled with the pituitary, it also regulates hormones related to mood and survival.
The amygdala allows for emotional discrimination. The amygdala is heavily involved in the fight, flight or freeze response. More explained in the video from the legendary neurologist, Rhawn Joseph (see below).
In addition, there are other parts the fornix and the olfactory cortex, their functions are not well known. For the fornix, it is made of the bundles of the axons that join the hippocampus to the hypothalamus. For the olfactory cortex, it receives various inputs from the chemoreceptors present in the nose bypassing the thalamus.