[Mristudio-users] Does the inferior fronto-occipital fasciculus exists?

[susumu mori]

Hi Naama,

This is a good question and please allow me to share my though with people
in the MriStudio mailing list.

When we describe white matter, there are two ways. Let me use the analogy of
geological maps. If I see a map of Baltimore, there are essentially two
types of information; boundaries that define boarders of locations like
city, county, and state. The other is road information like route 95 that
travels from Washingon DC to NY. The former defines locations and the latter
doesn't belong to any single location.

Likewise, WM map has two ways to define. Many WM names define locations,
like the internal capsule, which is a WM location between the basal ganglia.
There are many "roads" that penetrate the internal capsule like
cortico-thalamic, thalamo-cortical, cortico-spinal, cortico-pontine, to name
few, but they are all intermingled and it's not possible to completely
decipher them, at least by DTI/MRI. There are also names of WM that imply
something similar to the road names. For example, the corticospinal tract
and IFO defines two destinations.

Our atlas obviously defines locations; all segments are defined by boarders.
Some of the defined locations have names that implies roads (e.g. IFO, SFO,
CST, ets), but they actually define locations. This is one source of
confusion.

Now, there are some more confusing things. I believe many macroscopic
anatomical nomenclature is based on classic histology observations. The SFO
and IFO are assigned to large white matter bundles that sweep from front to
back, which look like connecting the frontal and occipital lobes, but I
don't think it was confirmed that there are actually axons connecting the
frontal and occipital lobes. Therefore, the foundation of the assigned names
are not as sound as the corticospinal tracts, which are confirmed in many
animals and human.

Now, we assigned some locations of the brain "SFO" and "IFO". There is not
doubt that there are large axonal bundles travelling front to back (or back
to front) in the designated locations. However, if one asks, "do you know if
these locations really contain axons connecting the frontal and occipital
lobes?", well, I must say, "not sure". To me, it seems like an issue of
nomenclature.

In any case, assignments of "road-type" names to the WM is a tricky effort
because even for the "corticospinal tract", the designated locations may
contain many other axons like cortico-pontine and cortico-bulbar axons. As
long as they are mixed in a microscopic level, we can only say, "this region
has high concentration of the corticospinal tract" and, to be strict, we can
always argue that it is not correct to give a binary definition to a place
like, "this is the corticospinal tract", because the "real" corticospinal
tract refers to axons that connect the cortex and the spinal cord, not to
many millimeters of anatomical locations visualized by MRI/DTI.

So, going back to your original question, there were controversy over the
existence of SFO and now IFO . In these cases what is discussed is "is there
really a large concentration of axons that connect the frontal and occipital
lobes in the WM locations called SFO/IFO?" How does it affect our study?
Well, for the IFO, maybe we should change the name of the location to "a
large WM bundle running front-back (green color) at the junction of the
frontal lobe and the temporal lobe". To me, the source of the problem is the
adoption of road names to refer to locations. As long as we use our atlas to
define locations and do quantitative measurements such as volumes and FAs,
how we call each location is not really a critical issue. Of course, it
could profoundly affect the interpretation. If the FA of "IFO" is low, we
should not immediately conclude connectivity problems between the frontal
and occipital lobes, simply based on the name of the location. In this
sense, you raised an important issue. On the other hand, IFO/SFO have been
widely used to refer some specific locations and we can communicate about
anatomical locations through these terms. So, even if they
are mis-nomenclature, we may need to keep using them unless the anatomist
society comes up with a new set of anatomical languages to refer these
anatomical locations.

Susumu

On Fri, Feb 18, 2011 at 5:07 PM, Naama Barnea-Goraly <naamab at stanford.edu>wrote:

>
> Dear Susumu,
>
> A recent analysis we are running yielded some significant results in the
> IFOF (according to the JHU White matter tractography atlas) which lead me to
> some investigation on this pathway. I was very surprised to read in " White
> matter of the Brain" ( a book by Schmahmann and Pandya), that in fact the
> IFOF does not exist (page 445). They think the IFOF is in fact the ILF
> /uncinate/extreme capsule mistaken by early anatomists as a separate tract.
> What do you think?
>
> Thanks,
>
> Naama
>
>
>
> Naama Barnea-Goraly M.D.
> Instructor
> Center for Interdisciplinary Brain Sciences Research
> Stanford University Division of Child and Adolescent Psychiatry
> 401 Quarry Rd. MC 5795
> Stanford University School of Medicine
> Stanford, CA  94305-5795
> Phone: (650) 736-1874, fax: (650) 724-4794
>
>
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