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Dear Jenny, Isak, and group, > > > > >As far as I can see, a REGIONALLY-specific task x drug interaction cannot > >be explained by a non-specific (ie. not regionally specific) effect of drug > >on the neurovascular pattern. In other words, to demonstrate a drug x task > >interaction (from which one can make cognitive inferences) the areas > >activated/deactivated by the interaction term should not be identical to > >those produced by the main effect of the task. > > > > > Of course, a 'REGIONALLY-specific task x drug interaction' is, by > definition, regionally specific. However, it may not necessarily be > metabolic, or 'cognitive'. For example, vascular innervation may be > regionally specific, or CBV may be different, giving rise to BOLD signal > changes that are only detectable in a particular region. Such effects would > be regionally specific, yet possibly uninteresting if not indicative of > local neuronal metabolic activation. > > I think Isak makes an excellent point. Even if the regions in which there exists an effect of task at the drug factor level of "no drug" and the regions in which there exists a task by drug interaction are not identical, this still would not imply a drug effect on the neural activity associated with that task. To flesh out Isak's idea a bit with an example, say that at the drug factor level of "no drug", we observe a task effect in two regions X and Y. And we also observe a drug by task interaction only in region X. I think Jenny was arguing that since the interaction was regionally specific (i.e., present in X but not in Y), that this would imply an effect of the drug on the neural activity associated with the performance of the task. However (following Isak's point) what if the cerebrovasculature in region X was sensitive to the drug, while the cerebrovasculature in region Y was not? This could be an alternative explanation. Still, though, there would seem to exist a set of results which would not be amenable to such an alternative explanation. That would be the existence of an interaction of task and drug in regions at which there is no task effect at the drug factor level of "no drug". Isak, Jenny, any thoughts? Best, Eric Eric Zarahn Columbia University %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%