346 Neuroanatomy: Draw It to Know It
The Thalamus, Part 1 ( Advanced )
Here, in two separate parts, we will create a table to orga-
nize the many diff erent thalamic and metathalamic
nuclei into several anatomic groups and briefl y discuss
their functional roles. Across the top of the page, write
group, nucleus, function/connections. First, label the
anterior nuclear group. Indicate that it comprises the
principal anterior and anterodorsal nuclei; in nonhuman
species, the principal anterior nucleus is subdivided into
the anteromedial and anteroventral nuclei.^9 Show that
the anterior nuclear group communicates with the mam-
millary bodies and cingulate g yrus as part of the Papez
circuit.
Now, label the medial nuclear group. Indicate that
the dorsomedial nucleus is the most prominent nucleus
within this group, and show that it has important con-
nections with the prefrontal cortex.
Next, label the lateral nuclear group, which divides
into dorsal and ventral subgroups. Indicate that the
dorsal subgroup comprises the dorsolateral, lateral pos-
terior, and pulvinar nuclei. Th en, show that the dorsolat-
eral nucleus bundles functionally with the anterior
nuclear group and communicates with the limbic system.
Next, indicate that the lateral posterior and pulvinar
nuclei collectively form the pulvinar–lateral posterior
complex, which is involved in visual attention. Th e pulv-
inar relays visual input from the superior colliculus to
the visual cortex as part of the extrageniculate visual
pathway.
Now, show that the ventral subgroup of the lateral
nuclear group comprises the ventroanterior, ventrolat-
eral, and ventroposterior nuclei. Indicate that the ven-
troanterior nucleus receives projections from the basal
ganglia, most notably, and that the ventrolateral nucleus
receives cerebellar and red nucleus projections as part of
the corticopontocerebellar pathway, most notably, but
indicate that it also receives basal ganglia projections, as
well. Both the ventroanterior and ventrolateral nuclei
project to the motor cortex. Note that there is inconsis-
tency in the literature regarding whether the ventroante-
rior nucleus projects to primary motor cortex as well as
premotor cortex or simply premotor cortex and there is
inconsistency as to whether its aff erent fi bers are primar-
ily from the basal ganglia or cerebellum.^10
Next, indicate that the ventroposterior nucleus sub-
divides into medial and lateral nuclei, and show that the
ventroposterior medial nucleus receives sensory aff erents
from the face and that the ventroposterior lateral nucleus
receives sensory aff erents from the body. Th e ventropos-
terior inferior nucleus, a less commonly discussed
nucleus, also exists. Sensory information in the thalamus
has a very specifi c somatosensory map in which the fi st is
adjacent to the mouth. Small ventroposterior strokes in
the lateral portion of the ventroposteromedial nucleus
and medial portion of the ventroposterolateral nucleus
result in the characteristic cheiro-oral syndrome in
which there is loss of sensation around the mouth and in
the fi st contralateral to the side of the thalamic infarct.
Now, label the posterior nuclear group, which lies
beneath the pulvinar and spans posteriorly from the
caudal pole of the ventroposterior nucleus to the medial
geniculate nucleus and also extends medial to the medial
geniculate nucleus. Show that it comprises the posterior,
limitans, and suprageniculate nuclei. Th e posterior
nuclear group has broad cortical connections; here,
simply denote the commonly cited secondary somatosen-
sory cortical projections of the posterior nucleus, which
are involved in nociceptive sensory processing.^3 , 8 , 11 , 12
We complete the table, next.