Dear Spm experts,
We have performed an fMRI expt to examine the effects of experimental mood
induction on verbal fluency activations on bipolar patients and normal
controls. Three blocks of scans are obtained, one in each mood state (
happy, sad, neutral)while subjects perform a verbal fluency task constisting
of epochs of generation repetition and rest.
We have specified two conditions: repetition and generation, and examined
contrasts -1 1 in all three mood conditions, to examine main effect of
verbal fluency.( ie. -1 1 -1 1 -1 1)
To examine the modulation of fluency activations by mood, we have compared
contrast -1 1 for scans obtained in the individual mood states (eg -1 1 0 0
0 0, if the first series of scans is obtained in Happy mood, and compared
the activations with those associated with contrast (0 0 -1 1 0 0) where the
second set of scans were obtained following sad mood induction.
To attempt to identify the main effect of mood, we have compared all scans
obtained in one mood state vs other mood states, eg ( 1 1 -1 -1 0 0). This
contrast does not identify any regional differences- we have used scaling to
remove global effects, and wonder whether this may have anything to do with
the problem
Could you advise us on how best to examine the main effect of mood in this
experiment.
We would also be interested in performing a further analysis, constraining
the comparison of fluency activations across all mood states to areas
activated by verbal fluency following neutral mood induction, could you also
help with advice about how best to do this.
With thanks, David Barbenel, Alan McBride
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