Trevor - there is certainly evidence that cytoarchitectural areas
differ both in their location and extent across subjects, suggesting
that there will not be any one-one mapping of location and structure
between subjects (e.g., Amunts et al. for Broca's area, Rajkowska &
Goldman-Rakic for dorsolateral prefrontal cortex). You are correct
that this creates difficulty in interpreting voxel-based analyses. The
field generally glosses over this by smoothing the data to an extent
sufficient to overcome this variability.
cheers
russ
On Mar 7, 2005, at 3:14 AM, Smart, Trevor wrote:
> I am relatively new to fMRI and the mailing list and my question may be
> rather naive. I was hoping to do the same as Eli - map the
> coordinates of
> the standard fMRI space (eg Telairach) to regions of the structural
> brain
> atlas. If I understand your point, functional maps do not map directly
> to
> structural maps as everyone is different. Instead a probabilistic
> approach
> can be used. However, how does this relate to differences between
> individuals in their functional maps. If there was no difference, then
> couldn't an atlas be redefined functionally? If this still remains a
> probabilistic map because of inter-subject variability then isn't this
> a
> problem for the smallest region we can identify - a voxel. If this is
> the
> case, does this create issues in interpreting voxel by voxel analyses?
> This
> seems quite fundamental, but probably just reflects my lack of
> experience in
> the field.
>
> Trevor
>
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping)
> [mailto:[log in to unmask]]On
> Behalf Of Russ Poldrack
> Sent: 04 March 2005 20:58
> To: [log in to unmask]
> Subject: Re: [SPM] Talairach database
>
>
> Eli - this is a FAQ and I feel like a broken record, but here goes:
>
> The idea of an automated one-to-one mapping between stereotactic
> locations and anatomical structures is highly problematic. The fact
> that the Talairach atlas (and sites like the Talairach Daemon) support
> this function does not make it any less problematic. There are a
> couple of problems. One is that volumetric spatial normalization does
> not absolutely align structural features; that is, if you normalize all
> of your subjects to a common space, and then classify which particular
> brain bits fall at a particular location for each subject, you will see
> that there is not perfect alignment across subjects. Various people
> (e.g., the MNI group) have produced probabilistic atlases showing this,
> and some of this information is available through the Talairach Daemon.
> Thus, the best you can do is say that you are in a particular
> structure with some probability.
>
> Second, there is the issue of structure-function association. Work by
> Amunts and a number of others has shown that cytoarchitecture (e.g.,
> Brodmann's areas) does not follow gyral anatomy. This is particularly
> the case in places like prefrontal cortex (e.g., see Amunts' work on
> area 44/45). Thus, you can't simply go from a stereotactic location to
> a Brodmann's area.
>
> Third, the Talairach atlas presents what are essentially guesstimates
> about where particular Brodmann's areas fall - they are not based on
> direct histology of the Talairach brain. Going from Talairach
> coordinates to Brodmann's areas by means of the Talairach atlas is thus
> highly suspect.
>
> I will not pretend to have the right answer to this question, but the
> approach that I try to instill into my students is to actually
> understand the anatomy where they are seeing activation, looking both
> at group maps and individuals. This is best done by working with a
> high-quality anatomical atlas; we like the Duvernoy atlas. In the end
> the goal should be to have a good enough 3-D mental model of brain
> anatomy that you can do this without the atlas, but that takes a long
> time indeed.
>
> If you feel really strongly about localizing to Brodmann's areas, then
> one approach is to use the probabilistic maps created by the Julich
> group (http://www.fz-juelich.de/ime/ProbabilityMaps_eng.html). With
> these maps, you can provide a probability that your activation is in
> any of the particular areas for which there are maps. Unfortunately
> these are only available for a limited number of areas.
>
> I recommend that you read Matthew Brett's paper on localization in
> functional imaging, which discusses these and other issues quite
> nicely.
>
> cheers,
> russ
>
>
>
> On Mar 4, 2005, at 11:55 AM, Eli Packer wrote:
>
>> Hi,
>> I need a way to translate voxel coordinates to their corresponding
>> regions. This is the task of Talairach. I saw that there are applets
>> that can be downloded but it will not help me since I want to use this
>> database in my own code. I also do not want to be involved in
>> converting SPM code or such. Just a simple database with pairs of
>> coordinate and regions is enough. Any ideas how to obtain it?
>>
>> Thanks a lot,
>> Eli Packer
>>
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> ---
> Russell A. Poldrack, Ph.D.
> Assistant Professor of Psychology, UCLA
> Franz Hall, Box 951563
> Los Angeles, CA 90095-1563
> email: [log in to unmask]
> phone: 310.794.1224
> fax: 310.206.5895
> web: http://www.poldracklab.org/
>
>
>
>
---
Russell A. Poldrack, Ph.D.
Assistant Professor of Psychology, UCLA
Franz Hall, Box 951563
Los Angeles, CA 90095-1563
email: [log in to unmask]
phone: 310.794.1224
fax: 310.206.5895
web: http://www.poldracklab.org/
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