The Situationist

Posts Tagged ‘transcranial magnetic stimulation’

Nancy Kanwisher on the Situation of our Brain

Posted by The Situationist Staff on August 25, 2009

BrainFor Observer, publisehd by the Association for Psychological Science, Ann Conkle wrote a nice summary of Nancy Kanwisher‘s fascinating keynote address at this years APS Annual Convention in San Francisco.  Here are some excerpts of Conkle’s article, titled “Sharpening the Focus on Brain Function.”

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Is your brain like a Swiss Army knife? . . . Is it jam-packed with specialized tools that are unfolded only when a specific situation arises? Or is it more all-purpose, with a few parts that tackle many different situations? Convention Keynoter and APS Fellow Nancy Kanwisher (Massachusetts Institute of Technology) is attempting to find out.

Following centuries of debate about specialized brain regions — from the phrenologists to Broca — the development of fMRI technology has ushered in a new era of studying brain regions. By monitoring the blood flow necessary to support neural activity, fMRI has allowed researchers to track which regions of the brain are involved in processing specific stimuli. With this new weapon in her arsenal, Kanwisher performed a now-classic study published in 1997. In it, participants sat in an fMRI scanner while looking a series of faces and objects. She and her colleagues identified an area in the fusiform gyrus on the bottom surface of the temporal lobe that responded more strongly when the participants viewed faces than when they viewed objects. Dubbed the fusiform face area, this region seemed like it could be specialized for processing faces.

But the researchers could not yet be sure. What if the area responded to everything animate, or everything round? A decade of more detailed research confirmed their original hypothesis — the fusiform face area lived up to its name. At the same time, Kanwisher’s lab discovered two other specialized areas: the parahippocampal place area, which specializes in processing places, and the extrastriate body area, which specializes in processing images of the body.

These answers only lead to more questions. These areas are involved in processing certain categories, but do they merely process perceptual input or actually reflect conscious experience? What are the roles of genes and experience in wiring up these areas? And finally, how much of the brain is like this? Is our entire cortex broken up into small pieces, each with their own special domain? Kanwisher and her colleagues are tackling these questions head on.

Do these areas only engage in their respective categorical processing or do they perform other functions as well? For example, take the fusiform face area. It is most active when viewing faces, but it also shows lesser activity when the participant is looking at other visual stimuli, like objects. Something in the pattern of this lower activity could be crucial in processing input other than faces. Evidence against this idea comes from research on patients with neurological trauma, who sometimes lose face perception abilities without losing object perception. But, the low chance of finding subjects with a lesion in just the right spot make this research limited. Other researchers have turned to transcranial magnetic stimulation (TMS), a method that uses magnetic fields to transiently disrupt neural activity. The fusiform face area is too deep in the brain to be affected by TMS, but the extrastriate body area is closer to the scalp and susceptible to the TMS disruption. When the neural activity in this region is disturbed, participants are impaired in the ability to recognize bodies but have no difficulty recognizing faces or other objects. Although these specialized areas may collect information about other types of stimuli, it seems that they are only necessary for processing information of their specific type.

Are the functionally specific regions merely perceptual processers or do they reflect our conscious experience? To illustrate the difference between perception and experience, Kanwisher instructed the audience to pick up the 3-D glasses left on the seats. But, before we could put them on, she showed us two images, a red-tinted image of a face and a green-tinted image of a house. Then she superimposed the house on the face creating a red/green face/house jumble. But, when looking at this jumble through glasses with one red-tinted and one green-tinted lens, so that the house image goes to one eye and the face image to the other, you don’t experience a jumble — you experience a red face that fades to a green house and back and forth as your brain attempts to make sense of this new situation. Even though your experience of what you are seeing is changing, the image beamed to your retina is constant the whole time. Work from Kanwisher’s lab showed that in this situation, activity in the fusiform face area corresponds with one’s experience, not with the actual perceptual input.

Further, not only does the activity in specialized areas correspond with what we consciously see, it also corresponds with what we imagine. Kanwisher has put people in the fMRI machine and asked them to imagine familiar faces and places. The same areas are active when participants are imagining faces and places as when they are actually looking at faces and places. It’s not just what you are physically seeing, but what you are consciously aware of that is processed by this area.

So, where do these specialized areas come from? What role do genes and experience play in their construction?

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For answers to those questions and the rest of Conkle’s summary of Kanwisher’s talk, click here.

To watch a video of Kanwisher’s Keynote presentation, click on the video below.

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For a sample of related Situationist posts, “Smart People Thinking about People Thinking about People Thinking” and ““The Grand Illusion” — Believing We See the Situation.”  To review a collection of Situationist posts on neuroscience, click here.

Posted in Classic Experiments, Neuroscience, Video | Tagged: , , , | 2 Comments »

 
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