Limbic System - What's in, What's out

David dhe at
Thu Feb 23 23:01:00 EST 1995

pn8886 at (Phil Nicholls) writes:

>I have been getting into the literature on the limbic system and
>I am having some problems with deciding what constitutes the limbic
>system.  Different authors list different sets of structures.  All
>seem to include the hypothalamus, amygdala, hippocampus and septal
>areas.  I am partial to Isaacson's views because it is rather clean.

>Is there any sort of consensus outside of these structures?

Not much.  Here's the list I give my students in Physiological
LIMBIC SYSTEM (may include some or all of the following,
depending which neuroanatomy text you read):
     1) the amygdaloid complex ("the amygdala" for short),
     including: the central nucleus, the corticomedial group of
     nuclei, the basolateral group of nuclei, and the lateral-
     basomedial group of nuclei
     2) the hippocampus
     3) parts of the hypothalamus, especially the mammillary
     4) ventral parts of the corpus striatum, such as:
          a) the nucleus accumbens
          b) the septal nuclei
     5) "limbic cortex" (the paralimbic system):
          a) the cingulate gyrus
          b) parts of the frontal cortex (especially
          orbitofrontal cortex)
          c) parts of the temporal cortex (such as the
          parahippocampal gyrus)
          d) the insula
     6) the anterior nucleus of the thalamus (because it links
     the hypothalamus to the cingulate gyrus)
     7) the olfactory bulbs
     8) the fornix (which is actually just a long bundle of axons
     linking the hippocampus with the mammillary bodies)

I could also have included several other fiber tracts (the stria
terminalis, the mammillothalamic tract, the lateral and medial
olfactory striae, the olfactory tract, the anterior commissure, the
ventral amygdalofugal pathway, the medial forebrain bundle, the
cingulum, and more).  Other structures I might have included are the
preoptic nuclei, a few midbrain nuclei, primary olfactory cortex, and
the habenula.  And more.

Basically, if it's involved in emotion, or if it's connected to
something that's involved in emotion, someone has probably called it
"limbic" at some point.

My main source for this is Terence R. Anthoney's extremely useful
_Neuroanatomy and the Neurologic Exam: A Thesaurus of Synonyms,
Similar-Sounding Non-Synonyms, and Terms of Variable Meaning_ (Boca
Raton: CRC Press, 1994).  Anthoney, with admirable compulsiveness,
pored through 24 neuroanatomy texts, seven neurology texts, and nine
texts on neurological examinations.  He catalogued their areas of
agreement and disagreement (and occasional self-contradiction) on a
few thousand terms, and arranged his findings encyclopedically.  The
centerpiece of his book is a few hundred short essays on such vague
terms as "limbic system," "basal ganglia," "prefrontal cortex,"
"septal area"--you get the idea.  He writes so lucidly that it's hard
to believe he's a scientist.  :)


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