Limbic System - Anatomy

Anatomy

The limbic system is the set of brain structures that forms the inner border of the cortex. The components of the limbic system located in the cerebral cortex generally have fewer layers than the classical 6-layered neocortex, and are usually classified as allocortex or archicortex.

The limbic system includes many structures in the cerebral pre-cortex and sub-cortex of the brain. The term has been used within psychiatry and neurology, although its exact role and definition have been revised considerably since the term was introduced. The following structures are, or have been considered to be, part of the limbic system:

• Hippocampus and associated structures:
  • Hippocampus: Required for the formation of long-term memories and implicated in maintenance of cognitive maps for navigation.
  • Amygdala: Involved in signaling the cortex of motivationally significant stimuli such as those related to reward and fear in addition to social functions such as mating.
  • Fornix: carries signals from the hippocampus to the mammillary bodies and septal nuclei.
  • Mammillary body: Important for the formation of memory;
• Septal nuclei: Located anterior to the interventricular septum, the septal nuclei provide critical interconnections
• Limbic lobe
  • Parahippocampal gyrus: Plays a role in the formation of spatial memory
  • Cingulate gyrus: Autonomic functions regulating heart rate, blood pressure and cognitive and attentional processing
  • Dentate gyrus: thought to contribute to new memories

In addition, these structures are sometimes also considered to be part of the limbic system:

• Entorhinal cortex: Important memory and associative components.
• Piriform cortex: The function of which relates to the olfactory system.
• Fornicate gyrus: Region encompassing the cingulate, hippocampus, and parahippocampal gyrus
• Nucleus accumbens: Involved in reward, pleasure, and addiction
• Orbitofrontal cortex: Required for decision making.