What is the limbic system?
In the human brain, the limbic system is “the regulator.”
As one of the oldest-known brain networks, the limbic system has been found to regulate many core brain functions, including response, reaction,1 behavior, emotion, memory, and learning.2
The limbic system has developed throughout the course of evolution to regulate core functions in mammals and humans. These processes often take the form of:
The response to a stimulus, such as a new smell, sound, or sight
The level of reaction or motivation, be it self-protection or reward-seeking
The behavior that ensues
The emotion associated with that response or behavior
The memories formed based on the experience
Any learning or takeaways from the experience
The limbic system was first named le grand lobe de limbique3 or the “great limbic lobe” by French neurosurgeon, Paul Broca, in 1878.4 Broca dubbed system as such because he found the limbic lobe to encompass several lobes4 that integrated with other core brain processes, such as olfactory and vision senses. It wasn’t until 1937 that American neuroanatomist, James Papez, identified the role the limbic system also plays in governing emotion.4
Where is the limbic system in the brain?
The limbic system generally includes the amygdala, thalamus, hypothalamus, hippocampus, as well as numerous functionally and anatomically-related areas that are considered paralimbic structures.5 These areas include the prefrontal-limbic system,2 anterior cingulate cortex (ACC), medial temporal network, parahippocampal gyrus, olfactory lobe, and the ventral tegmental area (VTA).2
Connections to other brain networks
As a primitive survival tool, the limbic system controls fundamental and core brain functions, such as alertness, motivation, and learning.2 As the human species developed throughout history, the limbic system evolved to play a role in more complex behaviors and functions (as is the case in our restaurant analogy).
To operate cohesively with the other important areas of the brain, the limbic system has key integrations with paralimbic areas, such as the orbital frontal cortex, intermodal frontal lobe, and the fusiform gyrus.
The limbic system also has connections to other brain networks for regulating key functional processes. The limbic system modulates:
The sensorimotor network for sensory perception, spatial reasoning, and motor commands
The language subnetwork for language processing
The olfactory system for analyzing smells6
The central gustatory system for the sense of taste14
The default mode network for memory, self-referential processing,15 and behavioral decision-making
While each brain network has key characteristics and processes, it is important to remember that every network modulates the interaction of other networks. None exist in a vacuum. Many connections in one network will activate connections in another network, and the limbic system may change or regulate how that activation works.
In addition to regulating the brain’s core processes, the limbic system can also determine how connections fire within other brain networks. And while it won’t directly impact another network’s functional connectivity, it changes the context in which other networks operate.
Though the limbic system has been an integral part of the human brain throughout our evolution, we are still uncovering connections between the limbic system and other brain networks. These discoveries will continue to give insight into how the limbic system regulates key processes and visceral emotions in our brain.