Hi Helmut
> Hi,
> A quick thought - would ASL-fMRI not be an option to circumvent most
> of the issues, especially the global scaling? If you are interested in
> such 'long-term' effects, ASL should be just fine...
For learning effects ASL might be better than usual BOLD though I'm not
an expert in that domain ... but I guess Markus already have his data
and try to find a way to get rid of the session effects ..
do you have any good ref on ASL and the pro/cons vs. BOLD? could be cool
cheers
cyril
>
> Helmut
>
>
> ----- Original Message ----- From: "cyril pernet" <[log in to unmask]>
> Sent: Wednesday, January 31, 2007 4:39 PM
> Subject: Re: scan pauses
>
>
>> Hi Markus
>>> dear spmer.
>>> a few weeks ago there was a question about a paradigm with scan
>>> pauses. i could not find any reply to this (neither could i find
>>> something in the archives). i have to ask almost the same question
>>> due to a paradigm, which needs scan pauses (due to the noise of the
>>> scanner).
>>> we explored the following paradigm:
>>> 60 scans baseline - 5 min pause with sensoric testing- 108 scans
>>> stimulation - 15 min pause with sensoric testing - 60 scans - 15 min
>>> pause with sensoric testing - 60 scans.
>>> we want to answer the BOLD-signal changes after the stimulation over
>>> a tine period of 50 minutes.
>>> now we have to face the problem of the interruption of the time series.
>>> here my questions:
>>>
>> ok I'll try - no warranties ...
>>> 1. is it absolutely impossible to conduct a paradigm with scanning
>>> pause (and why)?
>>>
>> I don't think so ... :-\
>>> 2. is there a time limit of the pause which would be tolerable?
>>>
>> well the time your subjects can stay in
>>> 3. is there any method, how we can test, whether the pause is really
>>> a problem or not (and not just theoretical)?
>>>
>> can help on this one
>>> 4. can we do something to solve this problem (like correction for
>>> global changes)?
>>>
>> yep - the global scaling should do the trick - or you can correct for
>> globals using another method see e.g. NeuroImage 22 p360 the paper by
>> Macey et al.
>>> 5. if we have to regard the 4 blocks as individual sessions, is it
>>> possible to use the first session (baseline) as the baseline
>>> condition and contrast all the other sessions with it?
>>> i would appreciate any commend about this very much (and even more,
>>> if it is not to technical).
>>>
>> well once it is corrected for globals it should be ok. Note that a
>> nice a way to look at the effect of learning is to use time as
>> parametric regressor .. I don't remember exactly how but for sure
>> you'll find details in paper from Henson et al.
>>
>> Hope this helps (a bit)
>> cyril
>>
>
--
Pernet Cyril, PhD
Center for Cognitive Neuroimaging
Voice Neurocognition Laboratory
Department of Psychology
58 Hillhead Street
University of Glasgow
Glasgow G12 8QB
Scotland
[log in to unmask]
http://vnl.psy.gla.ac.uk/
tel: +44 (0)141 330 4965
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