Dear SPM users
More recently we have performed a H2O-PET study to investigate the
functional neuroanatomy of prepulse inhibition (PPI) of the startle reflex
in normals, a measure of sensory gating or flitering (used in schizophrenia
rsearch). This paradigama implicates that a weak prepulse (PP)given shortly
before a loud pulse (P) reduces the eyblink response compared to the pulse
alone condition. In humans the blink reflex componend of the startle reflex
is measured using EMG of the orbicularis occuli muscle.
The design involves the following 3 conditions, replicated 3 times,
pseudorandomized
NS (= background noice),PP (=weak prepulse),P(=load pulse alone)
covariates measured with each condition:
NS : eyeblink amplitude( =0),PP: eyeblink amplitude; P: eyeblink amplitude
design used: NS P PP NS PP P NS P PPO
we have the following questions:
1) since brain activation using the starle pardigma is suggested to
habituate under the the pulse alone and possibly also under the
prepulse-pulse conditions, we wanted to use the coresponding eyeblink
amplitudes as "covariates" to weight each single scan or do we have to use
the amplitude measures as "confounding" variables to weight each scan for
each person so that we still can use contrasts?
Or do we have to weight the contrasts using the corresponding average of the
amplitudes measured during each scan?
2) To determine the activation/deactivation pattern between the first P and
the second P alone condition we used the following contrasts:
design: NS P PP NS PP P NS P PPO
contrats: 0 1 0 0 0 -1 0 0 0
is that correct?
3) what is the difference if we would have only used the first and second
pulse alone scans?
design: P1 P2
contrasts: 1 -1
Does a setting of a contrasts to 0 implicate that this scan is omitted or is
it still "somehow" included in the calculation of the total variance across
scans?
4) What is generally used for H20-PET : is it proportional scaling or ANCOVA
5) What number for extended threshold is normally used? And what does it
implicate?
Thank you very much for advice and suggestions!
Daniel Bächle
Psych. Uni-Klinik Zürich
Forschungungsabteilung
Lenngstr. 31
Postfach, CH-8029 Zürich
Tel. +41 (0)1 384 23 10
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