Atul Gawande also recently wrote a New Yorker article about treating phantom itch with Ramachandran’s mirror box. I found this part of Gawande’s article on statistical inference in perception most interesting:

You can get a sense of this from brain-anatomy studies. If visual sensations were primarily received rather than constructed by the brain, you’d expect that most of the fibres going to the brain’s primary visual cortex would come from the retina. Instead, scientists have found that only twenty per cent do; eighty per cent come downward from regions of the brain governing functions like memory. Richard Gregory, a prominent British neuropsychologist, estimates that visual perception is more than ninety per cent memory and less than ten per cent sensory nerve signals. When Oaklander theorized that M.’s itch was endogenous, rather than generated by peripheral nerve signals, she was onto something important.

I’m not familiar with this field but I wonder if anyone has tried to quantify what percent of our conscious experience that we normally believe to be 100% due to sensory input is actually recall from memory/inference based on past observation. Also, can this percentage adaptively change? Perhaps there are situations where the brain chooses to rely more heavily on memory and other cases where it relies more on primary sensory input.

NSF’s Emerging Frontiers in Research and Innovation (EFRI) office funded 4 very futuristic neuroengineering grants.

1. Deep learning in mammalian cortex
2. Studying neural networks in vitro with an innovative patch clamp array
3. Determining how the brain controls the hand for robotics
4. In vitro power grid simulation using real neurons

Disclaimer: I was involved with the second proposal on this page.

An extremely interesting trend in neuroscience has been to use the language of Control Theory to explain brain function. A recent paper by Shadmehr and Krakauer does a very nice job of summarizing this trend and assembling a comprehensive theory of how the brain controls the body. Using control theory, they put forward a mathematically precise description of their theory. Because their theory uses blocks that are direct analogues of specific brain regions like the basal ganglia, motor cortex, and cerebellum, they can use brain lesion studies to undergird their ideas about these components. From the paper:

The theory explains that in order to make a movement, our brain needs to solve three kinds of problems: we need to be able to accurately predict the sensory consequences of our motor commands (this is called system identification), we need to combine these predictions with actual sensory feedback to form a belief about the state of our body and the world (called state estimation), and then given this belief about the state of our body and the world, we have to adjust the gains of the sensorimotor feedback loops so that our movements maximize some measure of performance (called optimal control).

At the heart of the approach is the idea that we make movements to achieve a rewarding state. This crucial description of why we are making a movement, i.e., the rewards we expect to get and the costs we expect to pay, determines how quickly we move, what trajectory we choose to execute, and how we will respond to sensory feedback.

This approach of describing brain lesion studies in the context of a well-thought out theory ought to be further encouraged.

The concept that the brain holds maps of the surface of the body in the primary sensory and motor cortex is a fascinating but well known fact to the field of neuroscience since the early work of Wilder Penfield. What is less broadly appreciated is the concept of “peripersonal space”. A new book by Sandra and Matthew Blakeslee describes peripersonal space in the following way:

The maps that encode your physical body are connected directly, immediately, personally to a map of every point in that space and also map out your potential to perform actions in that space. Your self does not end where your flesh ends, but suffuses and blends with the world, including other beings. [...] Your brain also faithfully maps the space beyond your body when you enter it using tools. Take hold of a long stick and tap it on the ground. As far as your brain is concerned, your hand now extends to the tip of that stick. [...] Moreover, this annexed peripersonal space is not static, like an aura. It is elastic. [...] It morphs every time you put on or take off clothes, wear skis or scuba gear, or wield any tool. [...] When you eat with a knife and fork, your peripersonal space grows to envelop them. Brain cells that normally represent space no farther out than your fingertips expand their fields of awareness outward, along the length of each utensil, making them part of you.

What I appreciate about this, besides the stretchy comic book characters that it makes me think about, is that it provides a powerful perspective to begin piecing together a mass of disparate neuroscience data, which the Blakeslee’s capitalize on.

You’ll recognize the name Sandra Blakeslee from her co-authorship with Jeff Hawkins in On Intelligence and with V.S. Ramachandran in Phantoms in the Brain. This new book continues in the spirit of illustrating the broader significance of surprising findings in neuroscience. It covers a lot of recent neuroscience research, including mirror neurons, place cells and grid cells, the insular cortex and neuroprosthetics. For anyone looking to get the quick picture of these frontier research areas, this book serves as an excellent primer. It does an excellent job of making connections to socially relevant topics such as the secrets of athletic excellence, underlying causes of eating disorders and the modern obsession with plastic surgery. I have come to believe that neuroscience will eventually provide concrete explanations for the metaphors we use and the spooky phenomena we believe in but science cannot prove. Along those lines, this book does a great job of describing brain mechanisms that may underly paranormal phenomena like auras and out-of-body experiences.

One of my favorite parts is chapter six, a short chapter with a Phantoms in the Brain feel that presents some extremely jarring clinical examples of neurological problems potentially caused by body map disorders. It describes cases of individuals who want to have their limbs amputated because they feel like they don’t belong to them, individuals who no longer get feedback from their limbs as if they have disappeared, as well as cases of one woman who felt like she had three arms and three legs. That these cases exist are fascinating in their own regard; that there exists a systems-level conceptual framework with which we might understand the underlying causes for them is utterly incredible.

The implications of these ideas to AI are significant. What kinds of intelligent systems can we build by assuming that they have ego-centric representations of objects in their peripersonal space, or by assuming that their motor intentions are tickled by watching the movements of other creatures? The implications for computational neuroscience are also significant. What kind of system of neuronal processors is capable of producing cells that are sensitive to peripersonal space? What information must flow into those cells, and where is that information available from in the brain? Along what channels and using which “algorithms” does your brain map the visual information of a person moving their limbs to the motor areas that control your limbs? Perhaps I’ll be able to read about these things in the next Blakeslee neuroscience tour de force.

The Body Has a Mind of Its Own: How Body Maps in Your Brain Help You Do (Almost) Everything Better
by Sandra Blakeslee (Author), Matthew Blakeslee (Author)
Random House Publishing Group

(Full disclosure: Sandra Blakeslee and Random House kindly sent us a copy of the book to review before their release date…thanks guys!)

From the department of “we are living in a sci-fi movie”, here’s a video of a bionic arm that uses “fluidic muscles”.

The original slashdot article is here.

See if you can hear the Starcraft sound effect at the beginning and end of the video… (only for the truly obsessed)

Recently, a company named AnyBots appears to have been able to build a humanoid walking robot whose gait is much more humanlike that Honda’s Asimo (If you aren’t familiar with Asimo, check it out)

The robot is named Dexter, and here’s a link to a blog explaining why its better than Asimo. From the blog:

There are of course biped robots that walk. The Honda Asimo is the best known. But the Asimo doesn’t balance dynamically. Its walk is preprogrammed; if you had it walk twice across the same space, it would put its feet down in exactly the same place the second time. And of course the floor has to be hard and flat.

Dynamically balancing—the way we walk—is much harder. It looks fairly smooth when we do it, but it’s really a controlled fall. At any given moment you have to think (or at least, your body does) about which direction you’re falling, and put your foot down in exactly the right place to push you in the direction you want to go. Practice makes it seem easy to us, but it’s a very hard problem to solve. Something as tall as a human becomes irretrievably off balance very rapidly.

This is important because robots that dynamically balance can handle arbitrary terrains and can withstand attempts to knock them over, much like the Big Dog robot we reported on earlier, whereas pre-programmed robots like Asimo cannot. If Honda were smart, they’d buy AnyBot ASAP.

Here’s a link to the Slashdot article on this.

(UPDATE 03-05-2007 – Upon closer inspection, it is clear that while the surgery has enabled the woman to have sensation in the nerves of her missing hand when the surface of her chest is touched, the arm she is fitted with at the time of publication did not relay sensory signals from the arm back to her chest. As soon as she is fitted with an arm that has the appropriate sensors, however, she will not have to undergo further surgery to have this kind of direct feedback. Thanks to astute readers for pointing this out.)

The Guardian reports on an article published today in the Lancet about a successful surgical procedure giving an amputee a bionic arm that both responds to motor commands from her remaining motor nerves to control it and provides sensory feedback to sensory nerves when it is touched. If there was any doubt left, the worlds of neural prosthetics and brain-machine interfaces have officially collided.

The Lancet article is accompanied by two movies of the woman using the arm that you should really check out.

Given the recent progress in the decoding of motor signals from the brain and older progress on sensory feedback from neural prosthetics, this was to be expected. Nonetheless, watching this woman use her arm brings the message home in a visceral way. The spooky thesis of MIT CSAIL’s Rodney Brooks that “we will become a merger between flesh and machines” is one step closer today.

From the article:

Targeted reinnervation surgery was successful in this young woman. Four independent myoelectric sites were created that allowed improved control of a motorised artificial arm. Transfer sensation also developed; when the patient was touched on her reinnervated chest skin, she perceived the sensation to be in her missing hand.

An additional comment in the Lancet explains targeted reinnervation surgery:

Rather than record from these nerves directly, Todd Kuiken and colleagues report in today’s Lancet their development of targeted motor reinnervation (TMR), in which the disconnected ends of peripheral nerves are reimplanted into proximal musculature. Contraction of these proximal muscles shows the intended activation of the missing distal muscles. When combined with a myoelectric prosthesis, a command in the CNS to open the hand travels through its usual peripheral nerves, is amplified by the associated patch of reinnervated muscle, and is detected by myoelectric sensors, which trigger the prosthetic hand to open.

Todd A Kuiken, Laura A Miller, Robert D Lipschutz, Blair A Lock, Kathy Stubblefield, Paul D Marasco, Ping Zhou and Gregory A Dumanian, Targeted reinnervation for enhanced prosthetic arm function in a woman with a proximal amputation: a case study, The Lancet, Volume 369, Issue 9559, 3 February 2007-9 February 2007, Pages 371-380.

Though my queries may seem a bit ameteuristic, it is very important for me to get clarity on these doubts.
Hope my queries will be answered.
Thanking all of you in advance,
sudhi

The movie has to be seen to be believed. The robot is called BigDog and it looks like a CGI special effect. But don’t let the film industry desensitize you from the accomplishment here. The robotics engineering required to do this on real terrain is extraordinary. The engineers over at Boston Dynamics really deserve kudos for this.

These questions appear to be answered with the discovery of a motor interneuron in the cricket that is resposible for “corallary discharge” or forwarding neural signals from motor systems to sensory systems. By inhibiting auditory neurons during chirping, the animal can “counter the expected, self-generated sensory feedback”.

Over at the synapse blog, it is pointed out that the cerebellum may have this function in vertebrates.