Dear Drs Tanaka and Michimata,

If you wish to use basis functions to model activity related to cues,
instructed delays and probe/response events, I would certainly ensure that
the delay intervals are as variable as possible. Otherwise, there will be
some degree of correlation between the cue and the probe events,
particularly if there are protracted haemodynamic responses that last well
beyond your 10 sec. In such event, you will not be able to disabmiguate
between activity related to the cue, to the probe and to the delay interval
itself. For a description of appropriate methods, you may wish to look at a
paper by Toni e al. (1999) in Cerebral Cortex. This study has broadly
similar methodological requirements to yours.

Toni I, Schluter ND, Josephs O, Friston K, Passingham RE. Signal-, set- and
movement-related activity in the human brain: an event-related fMRI study.
Cereb Cortex. 1999 Jan-Feb;9(1):35-49.

In combination with methods by Toni et al., you may also wish to consider
increasing the trial-to-trial variation in the interval between the onset
of  a scan and the onset of the trial. In doing so, you will increase the
resolution with which you sample haemodynamic responses. I 'think' this is
summarised in the following reference:

Friston KJ, Fletcher P, Josephs O, Holmes A, Rugg MD, Turner R.
Event-related fMRI: characterizing differential responses. Neuroimage. 1998
Jan;7(1):30-40.

With best wishes,

Narender Ramnani

At 05:34 PM 2/6/01 +0900, you wrote:
>Dear SPMers,
>We have questions about how to apply basis functions to an Event Related
>fMRI experiment that involves different time course.
>
>It is a working memory experiment, and one trial consists of :
>Stimulus Presentation(6 to 14 sec, depending on different subject group) ->
>Delay(10 sec) -> Probe Presentation & Response(2 sec) -> baseline(16sec).
>TR is 2 sec, so that one trial has 17 to 21 scans. We have two subject
>groups and we are to compare the activation during the delay period between
>the groups.
>
>By searching the SPM mailbase, we come up with the following ideas:
>1. use  $B!H (Bhrf with temporal and dispersion derivatives $B!I (B to
>model the period
>of Stimulus Presentation, because this period has different length depending
>on subject groups.
>2.  Use  $B!H (BGamma function with derivatives $B!I (B to model the delay
>period.



>3. Use  $B!H (Bhrf with temporal derivatives $B!I (B to model the Probe
>Presentation &
>Response period.
>Are they correct? Are there any better ways?
>
>Second question is about carry-over effects. Our main interest is about the
>delay period. But if areas active during the delay period are also activated
>during the Stimulus Presentation period, then this pre-activation would
>seriously affect the hrf shape of the delay period, so that we would fail to
>detect activation in these areas. How one could avoid this?
>
>Any comments are welcome and we thank you in advance.
>
>Satoshi Tanaka
>Chikashi Michimata, Ph.D
>Cognitive Psychology Lab.
>Psychology Department
>Sophia University
>7-1, Kioi-cho, Chiyoda-ku
>Tokyo 102-8554
>Japan
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