310 Neuroanatomy: Draw It to Know It
Basal Ganglia: Nomenclature
Here, we will draw a fl ow diagram for the nomenclature
of the basal ganglia. Begin with the term corpus striatum ,
which comprises the caudate, putamen, and globus pal-
lidus. Indicate that the caudate nucleus, itself, is divided
into a head, body, and tail and that the globus pallidus is
divided into external (lateral) and internal (medial) seg-
ments. Striations connect the caudate and the putamen,
which are collectively known as the striatum. Th e stria-
tum is further subdivided into dorsal and ventral divi-
sions. Th e dorsal striatum comprises the bulk of the
caudate and putamen, whereas the ventral striatum is lim-
ited to only the ventromedial caudate and putamen, but
the ventral striatum also encompasses the nucleus accum-
bens and select basal forebrain structures. Th e dorsal
striatum is involved in a wide array of processes, including
the sensorimotor circuits, whereas the ventral striatum
associates principally with the limbic system and is pri-
marily involved in emotional and behavioral processes.
Now, indicate that together the globus pallidus and
putamen are called the lentiform nucleus, due to their
collective lens-shaped appearance. Bundles of myeli-
nated fi bers traverse the globus pallidus, giving it a pale
appearance, so the globus pallidus is also commonly
called the pallidum. Just as the striatum divides dorsally
and ventrally, so the pallidum is further subdivided into
a dorsal pallidum and ventral pallidum. Similar to the
striatum, the dorsal pallidum refers to the bulk of the
globus pallidus, whereas the ventral pallidum refers to
the anteromedial portion of the globus pallidus that lies
below the anterior commissure. However, although we
consider the ventral striatum and ventral pallidum to be
divisions of the striatum and pallidum, here, certain texts
distinguish these ventral structures as entirely separate
nuclei (ie, they distinguish the ventral pallidum from the
pallidum, itself ). Also, note that because the globus pal-
lidus is derived from the phylogenetically older portion
of the brain — the diencephalon, and the caudate and
putamen are derived from the phylogenetically newer
part of the brain — the telencephalon, the pallidum is
sometimes referred to as the paleostriatum, whereas the
caudate and putamen are sometimes collectively referred
to as the neostriatum.
Th e corpus striatum also encompasses several fi ber
pathways that pass between the globus pallidus and the
subthalamic nucleus and thalamus: the ansa lenticularis,
lenticular fasciculus, subthalamic fasciculus, and thal-
amic fasciculus. Th ese fi bers comprise a considerable
portion of the white matter region inferolateral to the
thalamus, which is called the fi elds of Forel (aka preru-
bral fi elds or Forel’s Field H).
As a fi nal note, the subthalamic nucleus and substan-
tia nigra are functionally but not developmentally asso-
ciated with the basal ganglia; therefore, although they
are variably included as part of the basal ganglia, we do
not include them in our defi nition of the basal ganglia,
here, in accordance with the Terminologia Anatomica.