SSS 2010-02-10（在线收听）

It’s called functional magnetic resonance imaging, or FMRI. And some neuroscientists call it the greatest scientific advance of the last 25 years.  Because FMRI lets researchers look at the human brain in action.  By measuring blood flow, it produces colorful maps of the brain that display the actual activity of neurons—it’s the brain at work. 

That sounds great, right? Well, there are criticisms. One is that it really is quite slow. The blood flow response can take 2-5 seconds, but a thought can flash in milliseconds.

Well a study published in the Journal of Neuroscience found a way to get around this time lag in order to study the timing of activation in two related but separate regions of the brain.

Scientists predicted that viewing an emotionally charged photo would get the attention of the viewer’s amygdale which is the fight or flight area of the brain, even before part of the brain’s visual system got activated. Now if that happened, it would mean that we process an image as scary before we even register what it is.

But to test timing of activation between two brain regions requires a fast measurement tool, and an FMRI scan is too slow to see if there’s any difference in timing between when the amygdala cells fire versus when the visual cortex cells fire.

So instead of doing a whole brain scan, which is standard for FMRI studies, the researchers scanned a tiny 5 mm part of the brain that included a sample of the pertinent regions. And by limiting the imaging to this small slice they were able to get 10 scans per second instead of one scan every 2 to 3 seconds. So if there was a short lag between regions in the brain, they could catch it.

They showed participants positive images, for example, porn and negative for example, people being tortured, as well as a neutral image.

And results were in line with their prediction:  the emotional photos activated the amygdala well before part of the visual cortex.

So while there is still a permanent issue with timing and FMRI—because the blood flow response arrives about 5 seconds after brain cells fire—these researchers show that it’s possible to measure the relative difference between activation times in two brain regions. 

It might seem creepy that our brain can tell us to run before we fully visually identified exactly what we are running from – but I think we can agree, that’s a pretty good thing.

—Christie Nicholson