The limbic system is a set of brain regions that combine to control long term memory, emotion, and olfaction. There are many areas of the brain that are sometimes considered a part of the system, but the main ones are the amygdala, the hippocampus, the cingulate gyrus, the hypothalamus, the thalamus, and the fornix, all except the last of which are described here.
It has somewhat of a spotted history. As Wikipedia’s article explains, it was originally assumed to control emotion while the neocortex controls cognition, but evidence has since come out stating that the truth is more integrated than that (ie, both the limbic system and the neocortex process at least a little bit of both cognition and emotions). The journal mentions per year (via Scopus) have been declining for the search “limbic system” when normalized to the mentions of the word “brain,” as you can see here:
Nevertheless, the concept of a limbic system is still a useful paradigm for some scientific research. Brankovic (2008) used it as a general brain region where symptoms from patients suffering from depression would manifest themselves. Turner et al (2008) used it as general brain region that was affected when the ventral pallidum was activated in a rat model of Parkinson’s disease. Although it may not totally reflect the reality in the brain, it represents a simplifying assumption that may help spur research.
Inspired by CalTech’s Question #5 for cognitive scientists: “What is the limbic system?”
Turner MS, Gray TS, Mickiewicz AL, Napier TC. 2008 Fos expression following activation of the ventral pallidum in normal rats and in a model of Parkinson‘s Disease: Implications for limbic system and basal ganglia interactions. Brain Structure and Function 213:197-213. doi:10.1007/s00429-008-0190-4.
Brankovic SB. 2008 System identification of skin conductance response in depression – An attempt to probe the neurochemistry of limbic system. Psychiatria Danubina 20:310-322.