Thanks. I'm accustomed to thinking of imaging as revealing the locus of effect rather than necessarily the causal mechanism, and I forget there are people who think that way. (Not psychologists, I hope. This seems to be more prevalent among physicians and physicists.) For example, I think of Roger Tootell's work showing that the human analog of V5, which detects motion, also responds similarly to perceived motion as in the motion aftereffect phenomenon. Certainly we wouldn't want to say that V5 causes motion to be perceived.
I would go with the third variable conclusion myself. The area in which a difference is detected is connected to other brain areas as well, not to mention as you pointed out the role of behavioral changes. Just because no differences are detected doesn't mean no differences are present. I wouldn't go with the all-placebo explanation because as I recall, people do sometimes spontaneously recover from depression even without any treatment. Charlotte >At 2:31 PM -0500 1/2/02, Charlotte Manly wrote: >>In other words, it really _is_ all in their heads. ;) Seriously, though, >>one of the nice things about brain imaging methods is they provide >>somewhat more tangible evidence of things at the psychological level. But >>ya gotta wonder... If the study's authors didn't expect to find brain >>correlates of ameliorated depression in placebo responders, where did they >>expect to find a change associated with the placebo response? In the >>heart? > >I suspect that they took seriously the claims that fMRI studies were >identifying a _mechanism_ of action for antidepressants, and that therefore >the changes in brain function were an index of the cause of antidepressant >action. > >The key terms, of course, are "correlates" and "associated with". >Given the above assumptions of causality, they probably expected to find >different brain mechanisms involved with drug action and placebo effects. > >Their actual findings point to at least two conclusions: >1) Third variable. The changes in brain function were an index of >behavioral change, which could in term be produced _either_ by drug or by >placebo effect, rather than an index of a mechanism of change. >2) It's all placebo. The minor differences between the drug and placebo >effects were due to the discriminability of the side effects of the >antidepressants (true double blinding with psychoactive drugs is nearly >impossible). > >* PAUL K. BRANDON [EMAIL PROTECTED] * >* Psychology Dept Minnesota State University, Mankato * >* 23 Armstrong Hall, Mankato, MN 56001 ph 507-389-6217 * >* http://www.mankato.msus.edu/dept/psych/welcome.html * > -- ====================================================== Charlotte F. Manly, Ph.D. Psychological & Brain Sciences Assistant Professor 317 Life Sciences Bldg ph: (502) 852-8162 University of Louisville fax: (502) 852-8904 Louisville, KY 40292 [EMAIL PROTECTED] http://www.louisville.edu/a-s/psychology/ http://www.louisville.edu/~cfmanl01 --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
