Hello,
Sorry to bring up an old issue that has been discussed previously, but it seems reviewers sometimes ask authors to put in a disclaimer that PPI is completely agnostic on directionality; e.g., it's A <--> B rather than A --> B. Is this type of description an oversimplification of PPI?
I realize there are two interpretations of PPI effects, which are described in Figure 5 of Friston's 1997 paper.
1) context-specific modulation of effective connectivity: the psychological context modulates the contribution of Region A to Region B
2) modulation of stimulus-specific responses: Region A modulates Region B's response to the psychological context
Although neither interpretation rules out common inputs (e.g., Region C) or asserts that the observed connections are direct, is it safe to say that Region A contributes to Region B in a PPI model in which Region A was chosen as the seed region and Region B was observed to have a significant PPI effect? To be clear, that PPI effect is not saying that responses in Region A *cause* responses in Region B or that Region B can't contribute to Region A.
Thanks!
David
JISCMail - spm Archive - Re: Directionality of psychophysiological interaction (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=spm;3b6d55e7.99)
JISCMail - spm Archive - Re: Interpreting PPI directionality? (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=spm;b637122c.1004)
JISCMail - spm Archive - Re: PPI directionality (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=spm;8f72d9b.06)
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