Science Questions

How does an MRI scan "see" a hallucination?

Sat, 25th Sep 2010

Part of the show Neuroimaging

Question

Gregg Comaroff asked:

If a hallucination is seeing what isnít there, how would a brain scan then see the same thing which isnít there?

Answer

We put this to Professor Paul Fletcher and Professor Jack Gallant...

Paul -   I don't know if thatís a great metaphysical question.  I mean, the brain scanner is looking at how the brain behaves when it is seeing something that isnít there, so itís not so much interested or able to see the content of that although as weíve just heard from Jack actually, the possibility of seeing what the brain thinks is there is possibly something for the future.

 

Chris -   Any comment on that Jack?

 

Jack -   Yeah.  I think thereís growing evidence that when you have a visual hallucination, whatís actually happening is the visual areas of your brain are being activated, essentially top down from inside out and the visual experiences you have in the visual hallucination are Ėsince the brain subsystems were being operated in those cases are visual, then you both experience visual events and you could decode visual events because you're decoding from the same parts of the brain that are encoding visual information normally.

 

Chris -   And hence, what you've got is this system where you think itís real because itís the same bit of the brain that would say, ďYup, I'm experiencing somethingĒ but itís just being internally generated.

 

Jack -   Right.

 

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