yep, the precentral is posterior to Exner's but BA6 probably has, at least if we takes Brodmann's maps, some overlap.
Cheers,
Andreas
________________________________________
Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Matt Glasser [[log in to unmask]]
Gesendet: Samstag, 28. Mai 2011 17:50
An: [log in to unmask]
Betreff: Re: [FSL] AW: [FSL] Highly negatively correlated waytotal and average FA
It looks like Exner's area is not on the convexity of the precentral gyrus,
which are the connections I am concerned about. One certainly does get
arcuate connections dorsal to Broca's area in the Exner's area.
Probabilistic, observer independent area 6 does not extend into this region,
but I forgot that the Brodmann area does.
Peace,
Matt.
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Andreas Bartsch
Sent: Saturday, May 28, 2011 4:56 AM
To: [log in to unmask]
Subject: [FSL] AW: [FSL] Highly negatively correlated waytotal and average
FA
Hi,
it certainly extends to both. Parts of BA6 belong to Exner's area, so you
can trust it to be connected to temporal areas.
Cheers,
Andreas
________________________________
Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von hd x
[[log in to unmask]]
Gesendet: Freitag, 27. Mai 2011 18:30
An: [log in to unmask]
Betreff: Re: [FSL] Highly negatively correlated waytotal and average FA
Hi Matt,
It's interesting to discuss about the connection between BA6 and temporal
lobe, since recently I saw some papers claiming the arcuate fasciculus
actually ends in BA6, but not the classical Broca's.
I don't know if you have read this review which touched this issue:
http://brain.oxfordjournals.org/content/132/9/2309.abstract
For the crossing fiber problem, could you illustrate a bit what you meant by
" you might in fact be measuring a change in the arcuate (...) or SLF III..
"?
And the following-up question would be: does the probabilistic tracking
handle the crossing fibers so badly that I should not trust at all the large
amount of fibers I got between BA6 and temporal lobe?
Best,
hd
On 16 May 2011 22:47, Matt Glasser <[log in to unmask]<mailto:[log in to unmask]>>
wrote:
I don't believe there is a real connection between BA 6 and posterior
temporal cortex, as I have looked at higher and higher quality diffusion
data (better resolution, more directions, higher bvalue) and it becomes less
and less, as one does a better job of resolving the crossing fibers.
Granted these are my opinions, so your mileage may vary. :) To be convinced
I would have to see a strong suggestion in the data that you could
distinguish SLF III connections and arcuate connections in this region and
that you still found arcuate connections of higher probability than SLF III
connections. The issue is that you might in fact be measuring a change in
the arcuate (which I think goes to BA 44, 45, 47, and DLPFC) or SLF III
(which I think goes to BA 6 and 44) and attributing this difference to a
pathway that may not exist.
As for your other question, it has been published before:
Hua, K., J. Y. Zhang, S. Wakana, H. Y. Jiang, X. Li, D. S. Reich, P. A.
Calabresi, J. J. Pekar, P. C. M. van Zijl
and S. Mori (2008). "Tract probability maps in stereotaxic spaces: Analyses
of white matter
anatomy and tract-specific quantification." Neuroimage 39(1): 336-347.
But they weren't the only ones to have that idea.
Peace,
Matt.
________________________________
From: FSL - FMRIB's Software Library
[mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of hd x
Sent: Monday, May 16, 2011 3:44 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [FSL] Highly negatively correlated waytotal and average FA
Hi Matt.
Thanks a lot for these hints!
I never heard about using "a weighted (by probability) average of FA"
before. But it sounds very delicious. Could you recommend any reference on
this method?
As for the BA6-posterior temporal connection, our hypothesis doesn't care
which one or two fiber(s) it includes, as long as there are real fibers
exist. While the concern is that if the significant crossing fibers will
weaken the interpretation of the correlation between the behavior and the
waytotal?
Best,
hd
On 13 May 2011 20:05, Matt Glasser <[log in to unmask]<mailto:[log in to unmask]>>
wrote:
You could take a weighted (by probability) average of FA inside the
unthresholded pathway to avoid the possible interaction you mention. As for
the pathway you are attempting to track, there are significant crossing
fiber issues there and I have my doubts that there really is an arcuate
connection to BA6 vs a confusion between the arcuate and SLF III.
Peace,
Matt.
________________________________
From: FSL - FMRIB's Software Library
[mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of hd x
Sent: Friday, May 13, 2011 3:50 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [FSL] Highly negatively correlated waytotal and average FA
Hi Matt., I traced the pathway between BA6 and posterior temporal lobe. Thus
it goes along the arcuate fasciculus.
I suspect the corr. between FA and waytotal is caused by the low
thresholding. Pathways with larger waytotal numbers have more "marginal"
voxels survived after thresholding, which leads to smaller average FA.
How do you think?
On 12 May 2011 16:30, Matt Glasser <[log in to unmask]<mailto:[log in to unmask]>>
wrote:
Okay, I understand what you did. Are you tracking a pathway along a
non-primary fiber orientation? That could cause a negative correlation
between waytotal and FA (i.e. the stronger the pathway, the lower the FA
because of crossing effects). It would help to know the pathway as well,
but if you don't want to publically say, you could tell me off list.
Peace,
Matt.
________________________________
From: FSL - FMRIB's Software Library
[mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of hd x
Sent: Thursday, May 12, 2011 1:49 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [FSL] Highly negatively correlated waytotal and average FA
Hi Matt.,
I made an error in describing how I normalized. I didn't divide the
waytotal, but divided the number of streamlines per voxel along the pathway.
But in case you got what I meant, are you suggesting to take the average FA
on a not-thresholded pathway?
Best,
HD
On 11 May 2011 18:33, Matt Glasser <[log in to unmask]<mailto:[log in to unmask]>>
wrote:
What happens if you don't do this normalization.
Peace,
Matt.
________________________________
From: FSL - FMRIB's Software Library
[mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of hd x
Sent: Wednesday, May 11, 2011 3:53 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [FSL] Highly negatively correlated waytotal and average FA
Dear list,
I'm working on a study examining the relationship between a behavioral
measure and a particular white matter pathway defined using probtrackx (part
of the arcuate fasciculus), and I found:
1. The behavioral measure is negatively correlated with the waytotal for the
pathway but positively correlated with average FA along the pathway.
2. There is a strong Negative correlation between waytotal and average FA
along the pathway.
The above two points seem to suggest something circular. Would this be due
to a problem of low thresholding or something related to the probabilistic
algorithm?
Ps, I divided the waytotal by the total sample sent out to normalize the
pathway and took a threshold of 5X10-6 .
Any thoughts or experience are highly appreciated.
Best regards,
hd
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