>The difficulty with this is that it is difficult to interpret a drug x task
>interaction in a region of the brain that is not activated by the task in
>the 'no-drug' or placebo condition and therefore this cannot circumvent the
>problem of differential gain response in different regions on drug. However,
>it is important to bear in mind that this should not invalidate the
>technique, particularly if your effects are predicted and meaningful.
>
Hello,
I've been following this discussion with much interest. This last point has
confused me somewhat. I'm not sure why the appearance of a task-related
effect in the presence of the drug (when there is no effect in the drug's
absence) should be difficult to interpret - or rather any more difficult to
interpret than the attenuation, augmentation or disappearance of a regional
task-related effect in response to the drug. Perhaps you could expand Mitul.
One other point implicit in Jenny Coull's first message but worth
considering more explicitly is that a regional drug by task interaction may
not be due to a non-specific vascular change, a regionally specific
vascular change or a directly pharmacologically mediated effect on regional
function. It could be a downstream effect of a drug-related change in the
way that subjects carry out the cognitive task. That is, if the effect of
the drug is to make the task in any way more demanding (or less demanding)
then task by drug interaction effects may reflect this change. Simply put,
subjects may deal with the activation task differently depending upon
whether or not they have the drug on board. If the drug makes it difficult
for them, they might engage new strategies to optimise performance. If the
drug makes it easier for them, they may dispense with strategies.
There is an important difference between this effect and what seems to be
the more common interpretation of drug by task interactions. The
difference between saying 'the drug changes the brain - different brain
equals different activation' and saying 'the drug changes the task -
different task equals different activation'
This extra ingredient in the pot is certainly not a reason for being put
off such studies though. Personally, I find it even more interesting.
Paul Fletcher
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