Walls in our minds

One of the biggest unsolved mysteries of science is how the brain encodes what we know, think about, and experience.

For many types of information, we know where in the brain they are stored.  But in what form, and how we retrieve it, is still not known.  As I tell my neuroscience students: think of something simple, like your middle name, the name of your first pet, the name of the first president of the United States.  Now: where in your mind was that information before I asked you to remember it?

Pretty bizarre to consider, isn't it?

Interpretation of sensory input is as mysterious as memory.  When I look around my office, where I'm currently writing this, I can recognize all sorts of objects -- my CD collection, books, the masks hanging on the wall, a wine glass hand-made by my son, an antique typewriter my wife got me for my last birthday.  But... how?  What's being projected onto my retina is just a bunch of splotches of light, shadow, and color, and my brain has to take that chaos and somehow make sense of it.  How can we tell where the edge of an object is?  How do we recognize things -- and know them to be the same objects if seen from a different angle, meaning the pattern of colors thrown onto your retina is completely changed?

Interestingly, there are some people who can't do this.  In apperceptive visual agnosia, usually caused by damage to the visual cortex of the brain, people are cognitively normal in every respect except that they can't recognize anything they see.  It all looks like a random moving kaleidoscope of colors.  Because in other respects they're normal, they can remember what they're told and respond appropriately -- if someone said, "Hey, you see that blob of blue and tan and brown over there?  That's a person, and he's named Gordon," a sufferer from apperceptive visual agnosia would be able to say, "Oh, hi, Gordon," and have a normal conversation with me.  But if I stood up (changing the shape of the blob of color) or changed my shirt, or made any other sort of alteration to what he's seeing, he'd no longer recognize me, not only as a particular human, but as human at all.  Because they're perfectly intelligent, he might be able to reason that since Gordon was over there a few seconds ago, and there's a different blob of blue and tan and brown nearby, that's probably Gordon, too, but it wouldn't be because he actually recognized me.  It would be a logical inference, not visual interpretation.

An interesting piece was added to the puzzle last week with a paper in Neuron that came from some research at Columbia University led by neuroscientist Nikolaus Kriegeskorte.  He and his team were investigating how we perceive walls -- how we know where the edges and barriers are in our environment, a pretty critical skill for spatial navigation.  By showing participants images with walls and other barriers and allowing them to navigate the space virtually, and using fMRI and magnetoencephalography (MEG) neuroimaging, they were able to narrow down where we do edge and obstacle processing to the "occipital place area" (OPA), one of the visual processing centers.

[Image licensed under the Creative Commons Pawel Wozniak, Brick wall close-up view, CC BY-SA 3.0]

"Vision gives us an almost instant sense where we are in space, and in particular of the geometry of the surfaces -- the ground, the walls -- which constrain our movement," Kriegeskorte said.  "It feels effortless, but it requires the coordinated activity of multiple brain regions.  How neurons work together to give us this sense of our surroundings has remained mysterious.  With this study, we are a step closer to solving that puzzle...  Previous studies had shown that OPA neurons encode scenes, rather than isolated objects.  But we did not yet understand what aspect of the scenes this region's millions of neurons encoded...  We would like to put these [data] together and build computer vision systems that are more like our own brains, systems that have specialized machinery like what we observe here in the human brain for rapidly sensing the geometry of the environment."

Once again, we have an idea of where our perception of barriers is housed, but not so much information about how it's stored or accessed.  How, when we see a wall -- especially, as in this experiment, a two-dimensional representation of a wall -- do we recognize it as such, and not just as a smear of colors, lines, and angles?  As Kriegeskorte said, we're a step closer, which is fantastic -- but still a long way away from solving the puzzle of perception.

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When the brilliant British neurologist and author Oliver Sacks died in August of 2015, he was working on a collection of essays that delved into some of the deepest issues scientists consider: evolution, creativity, memory, time, and experience.  A year and a half ago, that collection was published under the title The River of Consciousness, and in it he explores those weighty topics with his characteristic humor, insight, and self-deprecating humility.

Those of us who were captivated by earlier works such as The Man Who Mistook His Wife for a Hat, Musicophilia, Awakenings, and Everything in its Place will be thrilled by this book -- the last thoughts of one of the best thinkers of our time.

[Note:  If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

In the mind's eye

I've always found Charles Bonnet syndrome fascinating, and it's not just because the disorder was named after a scientist with whom I share a last name.

Nota bene: Bonnet is definitely not a relative of mine.  He was Swiss, whereas my father's family comes from the French Alps.  Plus, my dad's family name was changed when his great-grandfather emigrated to the United States -- it was originally Ariey.  In that area of France in the 19th century, there were often many branches of families living in a region, and the different branches were distinguished by adding the name of the town they were from as a hyphenated suffix.  My ancestors were Ariey-Bonnet -- Ariey from the town of St. Bonnet -- but when they came over, the immigration officials couldn't handle hyphenated names, so they just dropped the hyphen and Bonnet became the last name.  Just as well.  I have a hard enough time getting people to spell Bonnet correctly, I can't imagine what a pain in the ass it'd be to try to get people to spell Ariey correctly.

But I digress.

Charles Bonnet syndrome is sometimes called having "visual release hallucinations."  It is most common in people with visual impairment, and an odd feature of the disorder is that the people who are seeing them know they're not real.  Most of the time, hallucinations of any sort are terrifying, but in CBS, the sufferer usually just learns not to worry about them.  "I know I'm seeing little elves in carriages rolling alongside me when I walk," one 86-year-old with CBS said.  "When you get used to it, it's actually sort of amusing."

CBS is most common in people with macular degeneration, the most common cause of visual loss in the elderly.  This disorder causes the death of cells in the macula, or the center of the retina (also called the fovea), resulting in holes in the visual field that make it difficult or impossible to drive, watch television, and read.  An estimated 40% of people with macular degeneration experience some level of Charles Bonnet syndrome, experiencing visual hallucinations from the simple (flashing lights) to the elaborate (a head of a brown-eyed lion staring at you).  And new research has begun to explain why partial visual loss can result in bizarre hallucinations.

[Image licensed under the Creative Commons William H. Majoros, Lion-1, CC BY-SA 3.0]

This week, a paper appeared in the journal Cell entitled, "Stimulus-Driven Cortical Hyperexcitability in Individuals with Charles Bonnet Hallucinations," by David R. Painter, Michael F. Dwyer, Marc R. Kampke, and Jason B. Mattingly, of the University of Queensland.  The researchers found persuasive evidence that the weird hallucinations in CBS occur because the loss of visual acuity in the middle of the retina triggers the peripheral parts of the retina (and the parts of the visual cortex they're connected to) to overreact -- to become, in the researchers' words, "hyperexcitable."  The authors write:

Throughout the lifespan, the cerebral cortex adapts its structure and function in response to changing sensory input.  Whilst such changes are typically adaptive, they can be maladaptive when they follow damage to the peripheral nervous system, including phantom limb pain and tinnitus. An intriguing example occurs in individuals with acquired ocular pathologies—most commonly age-related macular degeneration (MD)—who lose their foveal vision but retain intact acuity in the peripheral visual field.  Up to 40% of ocular pathology patients develop long-term hallucinations involving flashes of light, shapes, or geometric patterns and/or complex hallucinations, including faces, animals, or entire scenes, a condition known as Charles Bonnet Syndrome (CBS). 

Though CBS was first described over 250 years ago, the neural basis for the hallucinations remains unclear, with no satisfactory explanation as to why some individuals develop hallucinations, while many do not.  An influential but untested hypothesis for the visual hallucinations in CBS is that retinal deafferentation [loss of sensory information from one part of the body] causes hyperexcitability in early visual cortex.  To assess this, we investigated electrophysiological responses to peripheral visual field stimulation in MD patients with and without hallucinations and in matched controls without ocular pathology.  Participants performed a concurrent attention task within intact portions of their peripheral visual field, while ignoring flickering checkerboards that drove periodic electrophysiological responses.  CBS individuals showed strikingly elevated visual cortical responses to peripheral field stimulation compared with patients without hallucinations and controls, providing direct support for the hypothesis of visual cortical hyperexcitability in CBS.

What this highlights once again is how fragile our sensory-perceptive systems are.  Loss of input from one area is bad enough; but instead of it simply causing a missing chunk from the sensory field, it causes you to misinterpret the signals from the part of your sensory system that is still working.  

Hardly seems fair.

At least CBS sufferers know what they're seeing isn't real, and learn to live with elves and lions and flashing lights.  Much worse are disorders like hebephrenic schizophrenia, where people have visual or auditory hallucinations -- and can't tell them from reality.  How completely terrifying that must be!

It's fascinating, however, to compare how certain we are that what we're seeing is real, and the minor changes it takes to have us see something that's clearly not real.  Once again, "I saw it with my own eyes" is a poor guide -- whether or not we're seeing elves in carriages.

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In writing Apocalyptic Planet, science writer Craig Childs visited some of the Earth's most inhospitable places.  The Greenland Ice Cap.  A new lava flow in Hawaii.  Uncharted class-5 rapids in the Salween River of Tibet.  The westernmost tip of Alaska.  The lifeless "dune seas" of northern Mexico.  The salt pans in the Atacama Desert of Chile, where it hasn't rained in recorded history.

In each place, he not only uses lush, lyrical prose to describe his surroundings, but uses his experiences to reflect upon the history of the Earth.  How conditions like these -- glaciations, extreme drought, massive volcanic eruptions, meteorite collisions, catastrophic floods -- have triggered mass extinctions, reworking not only the physical face of the planet but the living things that dwell on it.  It's a disturbing read at times, not least because Childs's gift for vivid writing makes you feel like you're there, suffering what he suffered to research the book, but because we are almost certainly looking at the future.  His main tenet is that such cataclysms have happened many times before, and will happen again.

It's only a matter of time.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Who watches the watchers?

A nearly universal, and rather creepy, sensation is when you turn to look at a stranger -- and find that they were watching you.

This "feeling of being watched" is something we all have experienced from time to time.  I seem to notice it most when I'm driving on the freeway, and happen to glance at the car next to me.  I can remember many times when either the person in the next car was already looking at me -- or else, even creepier, they turn their head toward me at exactly the same time.

However odd this feels, I've always felt like there was a perfectly rational reason for this, and my sense was that it's yet another example of dart-thrower's bias -- the perfectly natural human tendency to pay more attention to (or overcount) the hits, and ignore (or undercount) the misses.

In this case, how many times do you glance at a car next to you on the freeway, and the person in the car is not looking at you?  We don't remember it precisely because it happens so often.  On the other hand, on those rare occasions where someone is looking at us, it stands out -- and is given more weight in our memories.

"Uhhh... did you ever have the feeling that you was bein' watched?"

There's another possible explanation, however, and it has to do with an oddity of our perceptual systems only recently discovered because of a peculiar disorder called "blindsight," in which an individual is functionally blind, but can still perceive some visual stimuli.

Blindsight occurs when a person's visual cortex is damaged, usually by a stroke, but his/her eyes and optic nerve are still intact.  In a dramatic study led by Alan J. Pegna of Geneva University Hospital (Switzerland), it was found that although they are unresponsive to most visual stimuli, people with blindsight still exhibit visual phenomena like "emotional contagion" -- the tendency of people to match the emotions of faces they're looking at.

Apparently, this happens because the information from the eyes does not just travel to the visual cortex, it goes to a variety of other places in the brain, including the limbic system, which is the seat of emotion.  So a person might be able to match the smile in a photograph of a smiling person -- while not, technically, being able to see the photograph.

Pegna's study showed that not only are people with blindsight able to detect the emotion in a face they are (not) seeing, they can also tell when someone is looking at them.  Scanning results of a patient with blindsight showed increased activity in the amygdala -- the part of the limbic system that controls anxiety and fear -- when he was being watched.

So the conjecture is that there may be something more to the sensation of being watched than simple dart-thrower's bias.  It might be that when someone in our peripheral visual field is watching us, it doesn't register in our conscious awareness (through the visual cortex), but our nervous and ever-watchful amygdala still knows what's going on.  And since the limbic system largely functions subconsciously, it feels as if we had some kind of psychic awareness of something we didn't actually see.

Meaning that once again, we have a rational explanation (two, actually) of something that seems like it must be paranormal.  In other words: science wins again.  I have to wonder if something like this might be responsible for some other perceptual oddities, such as déjà vu, about which I have been curious for years but never seen a particularly convincing explanation.

In any case, it's something to keep in mind, for next time you're in a crowded restaurant and you see someone across the room staring at you.  It could be that your amygdala just went onto red alert.  It could also be that people are looking at you because you're drop-dead sexy.  You're welcome to go with whichever explanation you prefer.