The limbic system (from the Latin limbus, for "hem" or "border") is an assembly of linked structures that form a loose circuit throughout the brain. This system is a fairly old part of the brain and one that humans share with many other vertebrates; in reptiles, it is known as the rhinencephalon, or "smell-brain," because it reacts primarily to signals of odor. In humans, of course, the stimuli that can affect the emotional brain are just about limitless in their variety.5
Emotions have been defined as a group of interrelated superior cerebral functions, resulting from states of reward and punishment. It is currently accepted that the following areas participate in the majority of the emotional processes: prefrontal cortex, amygdala, anterior cingulate cortex, hippocampus, and insula creating a group of interconnected gray and white matter structures that create a loop in each cerebral hemisphere.. The amygdala is a large nuclear mass in the temporal lobe anterior to the hippocampus, called the amygdala which clearly plays a major role in the experience and expression of emotional behavior.1,3
The amygdala is a complex mass of gray matter buried in the anterior-medial portion of the temporal lobe, just rostral to the hippocampus. It comprises multiple, distinct subnuclei and is richly connected to nearby cortical areas on the medial aspect of the hemispheric surface. The amygdala (or amygdaloid complex, as it is often called) contains three functional subdivisions, each of which has a unique set of connections with other parts of the brain (figure C). The medial group of subnuclei has extensive connections with the olfactory bulb and the olfactory cortex. The basolateral group, which is especially large in humans, has major connections with the cerebral cortex, especially the orbital and medial prefrontal cortex. The central and anterior group of nuclei is characterized by connections with the brainstem and hypothalamus and with visceral sensory structures, such as the nucleus of the solitary tract. The amygdala thus links cortical regions that process sensory information with hypothalamic and brainstem effector systems. In addition to sensory inputs, the prefrontal cortical connections of the amygdala give it access to more cognitive neocortical circuits, which integrate the emotional significance of sensory stimuli and guide complex behavior.2
Individual differences in cognitive ability and social behaviour are influenced by the variability in the structure and function of the limbic system. A strong heritability of the limbic cortex has been reported, but little is known about how genetic factors influence specific limbic networks.
Injury to the prefrontal cortex or its underlying white matter results in a curious disability: the patient suffers from a reduced intensity of emotion and can no longer foretell the consequences of things that are said or done. (The injury must be bilateral to produce such an effect; if only one hemisphere is injured, the other can compensate and avert this strange, potentially crippling social deficit.)5
- Neuroscience. 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA)
- Price, J. L., F. T. Russchen and D. G. Amaral (1987) The limbic region II: The amygdaloid complex. In Handbook of Chemical Neuroanatomy, Vol. 5, Integrated Systems of the CNS, Part I, Hypothalamus, Hippocampus, Amygdala, Retina. A. Björklund and T. Hökfelt (eds.). Amsterdam: Elsevier, pp. 279–388.
- The Limbic System Conception and Its Historical Evolution. Marcelo R. Roxo, Paulo R. Franceschini, Carlos Zubaran, Fabrício D. Kleber, Josemir W. Sander
- Heritability of the limbic networks. Sanja Budisavljevic et al. 2016
- Discovering the Brain. Ackerman S.