Email to “The Skeptic’s Guide to The Universe” – FMRI

I haven’t had a chance to try to figure this out myself, but I recently posed the following question to “The Skeptic’s Guide to The Universe” to see if they could enlighten me.

The item they were discussing was the announcement that scientists could now, for all intents and purposes, image things that were viewed by test subjects using FMRI (Functional Magnetic Resonance Imaging).

Hi Guys (and Gal),

There is not much that I can say that hasn’t been said already about your awesome efforts in, not only maintaining a weekly schedule for this podcast, but also in constantly keeping it fresh and interesting. But I’ll add my voice to the many others who appreciate it and look forward to the fruits of your labor each week!

My question is regarding FMRI. Steve was emphasizing the fact that what you’re viewing is actually just blood flow and from that you infer greater or lesser brain activity in certain brain regions. What actually drives the change in blood flow? Neurons consume oxygen and glucose and release carbon dioxide and waste products, does the presence of the waste products (or the lack of presence of the fuels) cause the arteries to dilate? Or is the parasympathetic nervous system somehow in lockstep with the brain’s neurons and controlling arterial volume in response to, say, neuronal activity?
From my rather fuzzy perspective it seems that FMRI may actually be two rather than one inference away from the actual brain activity and, as such, would be a pretty crude approach to determining what is actually happening in there.

Is there any promising research that you know of that could allow direct detection of actual brain activity at the neuron level (i.e. detect adp/atp ratios or detect electrical activity at the cellular level)?

Looking forward to your insights,


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“It is easier to have a strong opinion when you lack information.”
– Michael Crichton

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