from
The Collaborative International Dictionary of English v.0.48
limbic system \limbic system\ n. (Anatomy, Neurophysiology)
A group of neural structures in the brain below the cerebral
cortex, centered on the hypothalamus and including the
hippocampus and amygdala, involved with control of emotion,
motivation, memory, and some homeostatic regulatory
processes.
[WordNet 1.5]
At the most ancient part of the human brain lies the
spinal cord; the medulla and pons, which comprise the
hindbrain; and the midbrain. This cobination of spinal
cord, hindbrain, and midbrain MacLean calls the neural
chassis. It contains the basic neural machinery for
reproduction and self-preservation, . . . MacLean has
distinguished three sorts of [more recent brain
structures controlling] the neural chassis. The most
ancient of them surround the midbrain. . . . We share
it with the other mammals and the reptiles. It probably
evolved several hundred million years ago. MacLean
calls it the reptilian or R-complex. Surrounding the
R-complex is the limbic system, so called because it
borders on the underlying brain. (Our arms and legs are
called limbs because they are peripheral to the rest of
the body.) We share the limbic system with other
mammals, but not, in its full elaboration, with the
reptiles. It probably evolved more than one hundred
fifty million years ago. Finally, surrounding the rest
of the brain and clearly the most recent evolutionary
accretion, is the neocortex. --Carl Sagan
(The Dragons
of Eden, New
York, Random
House, 1977).
[PJC]