Internal Capsule orientation

NMF nm_fournier at
Thu May 20 21:56:47 EST 2004

>     I am trying to figure out the main direction of the fibers of the
> internal capsule. Does anybody have an idea on this?

I don't think you realize the complexity of the question you asked.  Looking
at the internal capsule, at any level, will not tell you anything direct
regarding the major path of movement.  The majority of the fibers are
ascending thalamocortical projections or descending corticospinal (or
corticobulbar) fibers.  To complicate things further the internal capsule
(IC) can have fibers that are both ascending, descending, as well as locally
projecting (for example thalamic fasciulus).  Actually the IC is extremely
important for clinical neurological assessment because the different parts
of this mass of fibers correlates often with different deficits.

Thus, the fibers that make up the internal capsule do not necessarly project
in one unidirectional manner.  The internal capsule, therefore, represents a
collection of fibers of varying significance as to origin, course, and
functionality.  All of this, like everything in neuroanatomy, depends on
what level you are looking at, or to bring this back to our discussion at
what component of the internal capsule you are discussing (i.e. anterior
limb, genu, posterior limb: thalmolentricularis, sublentricularis,
postlenticrularis portions).  For example, the vast majority of fibers that
arise at the level of the anterior limb of the internal capsule (which in a
cornoal section lies between the head of the caudate and lenticular nucleus)
consists of the anterior thalamic radiations.  These are the major fibers
that make up the copious interconnections between the anterior and
dorsomedial thalamic regions and prefrontal and cingulate regions.
However, some of the fibers of origin are connections from the prefrontal
regions that project to those previously mentioned thalamic regions.  SO the
point being is that the fibers that make up the IC are not undirectional,
that is they do not project in one main direction.

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