More than fifteen years ago, neuroimagers found a region of the brain that seemed to be all about place. The region lies on the bottom surface of the temporal lobe near a fold called the parahippocampal gyrus, so it was called the parahippocampal place area, or PPA. You have two PPAs: one on the left side of your brain and one on the right. If you look at a picture of a house, an outdoor or indoor scene, or even an empty room, your PPAs will take notice. Since its discovery, hundreds of experiments have probed the place predilections of the PPA. Each time, the region demonstrated its dogged devotion to place. Less clear was exactly what type of scene information the PPA was representing and what it was doing with that information. A recent scientific paper now gives us a rare, direct glimpse at the inner workings of the PPA through the experience of a young man whose right PPA was stimulated with electrodes.
The young man in question wasn’t an overzealous grad student. He was a patient with severe epilepsy who was at the hospital to undergo brain surgery. When medications can’t bring a person’s seizures under control, surgery is one of few remaining option. The surgery involves removing the portion of the brain in which that patient’s seizures begin. Of course, removing brain tissue is not something one does lightly. Before a surgery, doctors use various techniques to determine in each patient where the seizures originate and also where crucial regions involved in language and movement are located. They do this so they will know which part of the brain to remove and which parts they must be sure not to remove. One of the ways of mapping these areas before surgery is to open the patient’s skull, plant electrodes into his or her brain, and monitor brain activity at the various electrode sites. This technique, called electrocorticography, allows doctors to both record brain activity and electrically stimulate the brain to map key areas. It is also the most powerful and direct look scientists can get into the human brain.
A group of researchers in New York headed by Ashesh Mehta and Pierre Mégevand documented the responses of the young man as they stimulated electrodes that were planted in and around his right PPA. During one stimulation, he described seeing a train station from the neighborhood where he lives. During another, he reported seeing a staircase and a closet stuffed with something blue. When they repeated the stimulation, he saw the same random indoor scene again. So stimulating the PPA can cause hallucinations of scenes that are both indoor and outdoor, familiar or unfamiliar. This suggests that specific scene representations in the brain may be both highly localized and complex. It is also just incredibly cool.
The doctor also stimulated an area involved in face processing and found that this made the patient see distortions in a face. Another study published in 2012 showed a similar effect in a different patient. While the patient looked at his doctor, the doctor stimulated the face area. As the patient reported, “You just turned into somebody else. Your face metamorphosed.” Here’s a link to a great video of that patient’s entire reaction and description.
The authors of the new study also stimulated a nearby region that had shown a complex response to both faces and scenes is previous testing. When they zapped this area, the patient saw something that made him chuckle. “I’m sorry. . . You all looked Italian. . . Like you were working in a pizza shop. That’s what I saw, aprons and whatnot. Yeah, almost like you were working in a pizzeria.”
Now wouldn’t we all love to know what that area does?
Photo credit: thisisbossi on Flickr, used via Creative Commons license
*In case you’re wondering, the patient underwent surgery and no longer suffers from seizures (although he still experiences auras).
Mégevand P, Groppe DM, Goldfinger MS, Hwang ST, Kingsley PB, Davidesco I, & Mehta AD (2014). Seeing scenes: topographic visual hallucinations evoked by direct electrical stimulation of the parahippocampal place area. The Journal of neuroscience : the official journal of the Society for Neuroscience, 34 (16), 5399-405 PMID: 24741031
I could not get the video to play, but it was interesting he described the face as having “metamorphosed”. My fusiform gyrus (facial recognition area in brain) was destroyed due to a stroke. I still see face the same. However, I have absolutely no ability to hold them in my memory. So they look the same, they just will never be remembered. I only see strangers now.
After I had brain surgery, a nurse brought me a Far Side comic. It was of neurosurgeons zapping areas of the brain and having the patient jerk his legs and arms. The doctors were laughing and saying, “Do it again.” Still makes me smile at what they were probably doing to me! 🙂
That’s fascinating. I have always wondered what it’s like to be face blind. It must have been so startling to discover the change after your stroke. Thank you for reading and sharing your story!
Hey. Thank you for sharing your story. I am one of the researchers on the new paper but I was hoping to maybe clarify some things. Most perceptions are not sums of their parts. By this I mean when one has normal face perception their idea of what a face ‘looks like’ does not include precise measurements of where things are in relation to one another. We might recognize the Mona Lisa but very few can answer questions like: What is she doing with her hands? Is her left or right shoulder more forward? OR EVEN what color is her hair?
It is an odd phenomenon when from time to time someone looks at a face (or watch or other known object) and actually sees what it REALLY looks like for the first time instead of the rough approximation that the brain commits to memory. People are very bad at seeing a pair of eyes and knowing whose eyes they are and even worse at knowing who someone is without seeing their eyes. When someone such as yourself loses this region you lose the ability to form this relational memory of the approximation. I would bet that if you were to draw someone’s face or study one small component as you would for an exam (for example: rehearse “mole half-way between earlobe and nose”) you might be able to recognize the person by seeing the mole and then checking against your memory of who the mole matches to. (I wish you luck in tackling this hurdle).
When researchers stimulate this area one of a few things might happen 1)The face skews as the person begins to see the actual features instead of the memorized approximation. 2) The face becomes grotesque as the area reports incorrect information (the FFA is very tied to visual areas and the current might be spreading OR the region itself is a node in a bigger network and being activated/inactivated messes with the signal as it moves through on its way to consciousness). 3) The stimulation of the FFA might drive its function. The face may have been changing to become more similar to a remembered face. The features would move to accomplish this goal.
Regardless this differs from it being wholly offline. When something happens to a region the brain often reorganizes to skip it or move function elsewhere. This region is pretty specialized so sadly full function doesn’t tend to come back but the pure unfiltered visual info does skip it and go to the conscious areas for processing. At that point instead of distortion you are getting a more true to life feed. During stimulation, the “morphing” was either the person experiencing the transition in a rapid fashion or a result of the signal getting tampered with.
I wish you the best in your future challenges and am glad that you seem to be well otherwise. Thanks again for your contribution. Hope I helped you understand what may be going on.