I'm still confused.
In order to see activation, you need to define the onset and duration
of the stimuli. From your description, its unclear if this can be
done.
Did you have the scanner running and then add chemical at T1 and then
continue to scan until the the chemical washed out - without stopping
the scanner?
Did you have the scanner running and then add chemical at T2 and then
continue to scan until the the chemical washed out - without stopping
the scanner?
Also, you generally want to have a first-level analysis and then
second-level analysis, but its unclear that this what was done.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Tue, Jan 22, 2013 at 7:43 AM, Engineer Syed
<[log in to unmask]> wrote:
> Dear all,
> There is only one session per subject. These are animal subjects so we keep
> them in the scanner, and time T1 we give them an injection, which is a
> chemical stimulation and at time T2 we again give them the injection in the
> other paw. So there is only one session per subject. I hope I m more clear
> now.
> It would be nice if someone can help me find the answer to my questions..
> Thanks a lot
>
> best regards,
>
>
>
>
> On Sat, Jan 19, 2013 at 12:08 AM, Chris Watson
> <[log in to unmask]> wrote:
>>
>> Do you do one session per subject, with stimulation & no stimulation the
>> experimental conditions? I don't understand what your task is.
>>
>>
>> On 01/18/2013 10:52 AM, Engineer Syed wrote:
>>
>> Dear SPM Experts,
>> I have set up one experiment and I m not sure whether I m doing it right
>> or wrong. I will tell the details of my experiment, and it would be great if
>> someone can comment if I m doing it right.
>> The experiment consists of 2 populations, one is control and the other is
>> patients. At time T1 each subject received a chemical stimulation in the
>> right paw and at time T2 in the left paw. These are animals subjects. As
>> seen from fMRI, we can visualize the change in the time series activity at
>> T1 and T2 in many of the brain region just by checking the time series,
>> which was very much expected. The "final goal" is to find out, which parts
>> of the brain have a different activation in two groups. In order to achieve
>> that I plan to go through these steps
>>
>> 1) I defined my null hypothesis separately for both populations that:
>> there is no effect when given the chemical stimuli. So contrast would be (1,
>> -1). Is that right ?
>> 2) I test the fixed effect analysis first, by first inputting all the
>> control subjects and applying the above mentioned contrast and analyze the
>> activations. Then I repeat the same with inputting all the patient/diseased
>> subjects with the same contrasts and analyse the activations. The hypothesis
>> would be that these two populations should differ in their activations
>> (because one group is control and one group is patients) Is that right ??
>> 3) In case I do not find any difference in activations; then I should not
>> do the random effect, since with high power of fixed effect if it didnt show
>> any difference there is no expected difference in random effects too !! Is
>> that right ??
>> 4) Can I make a 2x2 design here (healthy+chemical stimulation, healthy
>> without chemical stim., disease+chemical stim., disease without chemical
>> stim.) ???
>> 5) My hypothesis is that during the second chemical stimulation at time
>> T2, it would be a different reaction than the chemical stimulation at T1;
>> because these are different paws, and also because T2 might feel more pain
>> than the first stimulation of T1. How can I check my hypothesis ?
>>
>> Any comments will be highly appreciated
>> Thanks a lot
>>
>
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