Dear Claude,
|1) What's a good methodological procedure to study single subject?
I'm not sure that there is a good (short!) general answer to this
question, as it depends greatly on the specific question you are
interested in. For single case studies, one approach is to measure the
pattern of activation in your single case and qualitatively describe that
pattern with respect to normal functional anatomy. Often, however, a
quantitative comparison of a single patient and 'normals' is required.
This latter question raises issues of how many normals required and so on,
which has been covered in some earlier postings.
|2) Is there a minimum number of scans/condition and blocks suggested?
There is no exact answer to this I'm afraid, as it again depends on the
size and variability of the activations you are interested in
characterising, and hardware factors such as the field strength of the
magnet and the TR used. However...my (wholly subjective, and other people
will disagree) rule of thumb is 30 events/condition for an event related
design and 2 minutes (total over blocks)/condition for a blocked design,
per subject. Please don't take this as gospel, though: it can and will
vary according to stimulus, subject, magnet and cognitive process of
interest.
|3) Is it possible to have only 2 long blocks (rest and task) like in
|film presentation lasting several minutes?
Possible, but not recommended. Think of this in frequency terms. The
signal you are interested is the difference between task and rest, and
using a single long block means that the fundamental frequency of this
change is very low. Unfortunately many confounding signals of little
interest (physiologically aliased signals, drifts in scanner gain and so
on) also change at low frequencies. So it is bad to have experimental
signals and potential confounds changing at the same frequency. This is one
of the reasons why so many people use 30s blocks; the fundamental
frequency of the experimental signal of interest is taken out of the 1/f
noise. One place where you can find a description of this that might help
is Turner et al Exp Brain Res 123, 5-12.
I'm sorry my responses are so general but hope they will be of some help.
Best wishes,
Geraint
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Dr. Geraint Rees
Wellcome Advanced Fellow Lecturer
California Institute of Technology Institute of Neurology
Division of Biology 139-74 University College London
Pasadena 12 Queen Square
California 91125 London WC1N 3BG
voice (626) 395-2880 voice (171) 833-7472
fax (626) 796-8876 fax (171) 813-1420
http://www.klab.caltech.edu/~geraint [log in to unmask]
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