Comments on: Reading the Mindreading Studies

By: Justin Masterman

Justin Masterman — Mon, 27 Apr 2009 19:53:30 +0000

Neuroskeptic, thank you for your comments.

Vul’s critique unleashed a strong response from many in the media and the scientific community. I think it is important to remind people that these issues are not just for academic debate, but have real implications for our democracy as fMRI enters the courtroom. Statistical analyses aside, the use of fMRI raises a number of unresolved philosophical and psychological problems that demand sophisticated solutions.

By: Neuroskeptic

Neuroskeptic — Sun, 26 Apr 2009 22:22:36 +0000

While Vul’s argument is a sound one, it’s worth nothing that it has little to do with fMRI “lie detection” per se, which (as far as I know) doesn’t use the kind of whole-brain correlation analysis that Vul’s argument critiques.

Of course Vul is probably right when he says that No Lie fMRI is useless, but there are many diverse reasons for that…

On a related note, there is a new paper which makes a rather similar argument to Vul’s, but targeting a different kind of fMRI study: read about it here!

By: Justin Masterman

Justin Masterman — Fri, 24 Apr 2009 16:51:44 +0000

Thank you for your comments and clarification. Clearly, the source of the BOLD signal is extremely complex and contentious. With my appeal to astrocytes here, I was trying to highlight that the BOLD signal is not necessarily a direct measurement of the activity of computational neurons firing in response to stimuli. There is a lot more involved in the generation of the contrast. You are right to point out my oversimplification of the role of astrocytes, however.

By: bsci

bsci — Fri, 24 Apr 2009 14:33:15 +0000

You wrote:
Scientists have even discovered that blood flow through astrocytes, glial cells that are thought to play a largely supportive role in the brain, are the main source of the fMRI signal, not neurons.

This oversimplifies to the point of inaccuracy. The question isn’t where blood flows. Blood vessels don’t go “through” neurons or astrocytes. The question is what processes cause the blood flow and blood oxygenation changes that we can observe with the BOLD signal. Astrocytes seem to play a direct and major role in the process, but part of their role is uptake and transport of molecules involved with activity in neurons. Thus, part of their “support” role is causing blood flow changes. It gets much more complex than this and astrocytes seem to do more than support, but I just wanted to note that no one is talking about astrocytes vs. neurons with regard to the BOLD signal.

Also, for the Vul paper, in-press paper along with many formal replies and a rebuttal can be found on the journal’s site at:
http://www.psychologicalscience.org/journals/pps/4_3.cfm

Hope this helps.