376 Neuroanatomy: Draw It to Know It
Olfactory Cortex & Basal Forebrain, Part 2 ( Advanced )
Now, let’s group the anatomic structures we have drawn
into olfactory and basal forebrain listings. Begin with
the olfactory cortex. Divide it into medial, intermediate,
and primary (or lateral) cortices, which are innervated
by the medial, intermediate, and lateral striae, respec-
tively. Indicate that the medial olfactory cortex com-
prises, most notably, the subcallosal and paraterminal
g yri, which are collectively referred to (in this context)
as the medial olfactory area. Next, show that the inter-
mediate stria terminates in the olfactory tubercle within
the anterior perforated substance, which makes the
olfactory tubercle part of the intermediate olfactory
cortex. However, note that the olfactory tubercle is vari-
ably considered part of the primary olfactory cortex, as
well. Now, show that the primary olfactory cortex com-
prises the piriform cortex, periamygdaloid cortex, corti-
comedial amygdala, and a small portion of the entorhinal
cortex, anteriorly. Note that as we discussed previously,
the anterior olfactory nucleus is also variably listed as
part of the primary olfactory cortex. Also, note that the
distinction between the primary and secondary olfac-
tory cortices is highly variable; as an example, certain
texts include the entorhinal cortex as secondary olfac-
tory cortex rather than as primary cortex — many other
discrepancies can also be found.^8 , 14 , 25
Finally, let’s address the basal forebrain. Th e list of
structures that constitute the basal forebrain is inconsis-
tently defi ned throughout the literature; therefore,
here we will focus only on those structures that are nearly
universally grouped within the basal forebrain and
will disregard the less commonly affi liated structures.
Indicate that the following structures are commonly
considered part of the basal forebrain: the septal nuclei,
diagonal band of Broca, ventral pallidum, basal nucleus
of Meynert, substantia innominata, the corticomedial
amygdala, and the extended amygdala, which refers to
those areas of the basal forebrain with prominent con-
nections to the corticomedial amygdala: most notably,
the bed nucleus of the stria terminalis and the nucleus
accumbens. Note that the ventral pallidum and nucleus
accumbens are alternatively (or additionally) categorized
as part of the basal ganglia. Also note that the cortico-
medial amygdala is commonly organized along with
both the olfactory cortex and basal forebrain. And as a
fi nal note, consider that the piriform cortex in rats, the
animal model for olfaction, is extensive and functionally
important, but its size and signifi cance in humans
remains to be determined.^6 , 9 , 10 , 24 , 26 , 27