Does anybody know where my hand is?

Last week we talked about sensory feedback in robots. Now let’s take a moment to look deeper into sensory feedback in humans. I want to talk about a specific type of sensory feedback system called proprioception.

Neurologists often called our proprioceptive systems our hidden sixth sense, and in a lot of ways, they’re right to do so. Proprioception is an essential but little-thought-about system of feedback that gives our nervous systems information about the biomechanical position of our bodies. In other words, proprioception is the system of sensory feedback that tells us where and how active our body parts are in space. Neurobiologist T. J. Carew puts it this way: “Essentially, [proprioception] tells the central motor system how things are going out there in the peripheral world where the muscles are doing their job” (2000).  Most of us take for granted that feeling of knowing where our feet, hands, etc. are around us, but we wouldn’t be able to so easily know without proprioception. In fact, you’d have to look around you to find your own hand if it weren’t for the small bundles of nerves that make up our proprioceptive systems. These nerve bundles are constantly at work monitoring the tension and activity of our muscles and sending information into the central nervous system about the direction, position, and tautness of our limbs. Even when you are simply standing, sitting, or lying down, these nerves are at work making sure your body knows where it is. And it’s a good thing our proprioceptive system is so dedicated—without this constant input of information telling our central nervous system what’s what with our bodies, we’d all behave a lot more like Jell-O than usual.

That’s not to say life doesn’t go on without proprioception, but it does get a lot more difficult. In fact, there are people who lose their proprioceptive systems and have to learn to compensate. Oliver Sacks (an author whom I highly recommend) describes one such woman in his book The Man Who Mistook His Wife for a Hat (1970). In the chapter entitled The Disembodied Lady, Sacks describes Christina—a woman who loses her sense of proprioception after a bacterial infection. Christina goes “floppy as a ragdoll,” with no sense of where her limbs are. She has to learn to compensate for her lack of proprioception by using visual sensory feedback for every motion. Everything she does—from sitting up to picking up a pencil—she must visually monitor or else she loses track and cannot perform the operation. Because she lacks proprioception, Christina lacks the ability to feel her body and is uncertain of where it is around her. She and other sufferers of proprioceptive deficits are permanently stripped of what is normally a natural certainty of one’s own body. Quite literally, they are disembodied people. 

Carew, Thomas J. 2000. Behavioral Neurobiology. Sunderland (MA): Sinauer Associates, Inc. 

Sacks, Oliver. 1970. The man who mistook his wife for a hat and other clinical tales. New York (NY): Harper & Row, Pub.

More cool robots!

Hey everyone! In my last post I talked about Japanese robots that mimic elements of human cognitive functioning. You might also be interested in some robots that mimic locomotion that is similar to human movement. The Boston Dynamics group has built a robot called BigDog. BigDog can walk or run uphill, over obstacles, even in snow. BigDog may look more like a dog than a human, but like both dogs and humans BigDog is able to complete complex motion due in part to something called sensory feedback. 

Sensory feedback is very important to successful motor activity. Your body is constantly monitoring and adjusting itself based on sensory feedback about the tension, position, movement, etc. of your limbs.  Without sensory feedback, it would be very difficult to walk down the sidewalk or stand in line at the grocery store. In fact, without sensory feedback, you’d probably just fall over, limp. BigDog operates along the same principle. BigDog’s limbs receive information about the terrain based on how the limbs are flexing—just like your foot flexes and contracts to adjust to that crack in the asphalt. The result is the ability to move over rough ground successfully.  Check out how sensory feedback is working in this video of BigDog!

The Droid Life

Thirteen years ago, Japan began its “Century of the Brain” program. The ambitious program includes three objectives: Understanding the Brain, Protecting the Brain, and Creating the Brain. Yes, that’s right, creating the brain. In true Frankenstein fashion, the idea is that we can better understand the brain if we can build one. Simple enough, right?

But don’t picture grey goo in a jar in a mad scientist’s lab just yet. Japanese scientists are trying to simulate brains by building robots and computers that operate according to the same principles as our noggins. This is a good idea because while using cells and tissues to build a real brain might soon be possible, we would be limited in our ability to measure the functioning of free floating grey matter. Humanoid robots help us overcome this problem: we can build robots that operate like human brains but plug into sensors and other apparatuses that measure how the “brain” interacts with its environment. As a result, scientists are moving towards being able to measure learning, intelligence, even emotion in droid-like machines. 

C3PO, meet DB: DB’s 30+ skills include reinforcement learning, air-hockey, juggling and tennis swings. (Kawato 2008, Brain).

References:

Kawato, M. 2008. Brain controlled robots. HFSP J. 2(3): 136–142.

Kawato, M. 2008. From ‘Understanding the Brain by Creating the Brain’ towards manipulative neuroscience. Philos Trans R Soc Lond B Biol Sci. 363(1500): 2201–2214.

One Shot to Quit

Most smokers who try to quit without any help wind up failing in the long run. Behavioral counseling, nicotine replacement, and medications like buproprion (an anti-depressant) can be used by smokers with some success. Soon, smokers may benefit from a vaccine that will be even more effective than these other treatments in helping them smoke. The idea behind the vaccine is to stimulate the production of antibodies in the blood that will bind to nicotine. When the antibodies bind to the nicotine, the resulting molecule can’t get across the blood-brain barrier. In other words, the nicotine won’t make it out of the bloodstream into the brain—and the reinforcing activity in the brain associated with nicotine dependence will never get a chance to begin. Smokers who get the vaccine when it becomes available will find that smoking has lost all its cognitive and emotional rewards.

Shocking: Nicotine and the Brain

Nicotine has anti-anxiety properties, acts like a stimulant, increases cognitive function (including memory) and is connected to the emotional reward centers of our brains. No wonder it’s addictive! In fact, many clinicians agree that nicotine dependence (marked by cravings, withdrawal symptoms, and difficulty stopping tobacco use) is one of the hardest addictions to break. So how is it that nicotine affects the central nervous system so strongly?

The answer was found by studying a little-known animal called the torpedo ray.  The torpedo ray is a pretty cool animal—it has an electric organ that can generate a shock of up to 500 Volts.  If that doesn’t sound 

The torpedo ray uses the same molecules that respond to nicotine in our brains to deliver a killer shock to prey and predators. (Photo courtesy of flickr.com).

like much, know that it’s about the same amount of voltage generated by a commercial plane’s AC engine! How does the torpedo ray do it? The same way a smoker gets satisfaction from a cigarette—a molecule called the nicotinic acetylcholine receptor or nAChR.

In both the torpedo ray’s electric organ and our brains, nicotinic acetylcholine receptors (nAChRs) regulate how many charged particles flow in and out of our neurons. In the torpedo ray, this leads to a killer shock.  In our brains, this affects the level of neurotransmitters floating around, which in turn affects emotions and cognition. Normally nAChRs react with another molecule called acetylcholine that naturally occurs in the brain; but nicotine also reacts with nAChR. In fact, nicotine binds so well with nicotinic acetylcholine receptors that they were named after it! When the nicotine reacts with these receptors and binds to them, it acts like the volume dial on a stereo for neurotransmitters. Especially interesting are data that suggest that nicotine might increase levels of the neurotransmitter called dopamine in reward centers of the brain. There’s evidence that this is why people with psychiatric illnesses like anxiety and depression tend to have higher levels of nicotine dependence.

So the problem for smokers is that their brains like the nicotine too much—and respond to it too well. Too bad humans can’t harness our nicotinic activity like the torpedo ray does.

A 3D computer simulation of nAChR.

(Squire et al., ed. 2003. Fundamental

Neuroscience, 2nd ed.)

One More Thought on Blood-Brain Barriers…

Anyone in the pharmaceutical development biz knows that one of the biggest problem that drug developers face is drug delivery—how do we get the medicine to go to the right place in the body? If you read my last entry on blood-brain barriers, you might be able to guess that this problem is especially significant for neurological and psychiatric drugs.  If we want a drug to actually make it into the nervous system, it has to be able to pass the rather exclusive screening process of the blood-brain barrier.  For the most part, only small molecules that are lipid-soluble (i.e. dissolve in oily substances) make it into across the barrier into the oh-so-elite Brain Club. One reason that the drug Lithium Carbonate can be effectively used to treat Bipolar Disorder is because the lithium molecules are small enough to cross the blood-brain barrier. Antidepressants, alcohol, caffeine, and nicotine are also able to make it through.   Bigger, water-soluble molecules generally do not cross the blood-brain barrier.  Unfortunately, it’s these bigger molecules that are most often the ideal drugs for treating chronic neurological conditions.  Hopefully, someone will figure out soon how to get around the rules of that snobby blood-brain barrier.

If you want to know more on this topic, here’s an interesting article to check out: http://www.mcmanweb.com/blood_brain.html

I Brake for Blood-Brain Barriers

Your brain is an elitist.  Don’t make excuses. It’s just the way it is—and it’s a good thing.

Here’s what I mean—your brain, like the rest of your body, needs oxygen. And like the rest of your body, your brain gets oxygen from your blood.  But here’s the rub—there’s a lot of junk floating around in your blood. Take a sample of your blood and you’ll find all sorts of things—hormones, ions (charged particles), metals and the like all hanging out and taking a dip in the blood stream. For the rest of your body, this junk either serves a purpose or is usually fairly benign.  The functioning of your nervous system, however, is reliant on the chemical super-sensitivity of your neural cells, so we can’t have just any chemicals entering your nervous system willy-nilly or things would go to pieces. Hence the blood-brain barrier.  Here’s how it works:

Throughout most of your body, capillary walls are full of small openings that allow particles to diffuse in and out of the blood stream.  In the nervous system, these holes are sealed up, and the cells of the capillary walls are connected through what are called “tight junctions” (see diagram). Tight junctions keep particles from freely traveling from inside the capillary to outside the capillary and vice-a-versa.  The only way particles can move across the capillary wall is if they go directly through the cells that make up the capillary walls cells, and those cells are picky about what they let through. When the blood-brain barrier is tight and working, your brain function is protected from all the rubbish in your blood.  When the blood-brain barrier breaks down, neural function suffers.  In fact, the breaking down of the blood-brain barrier is associated with a number of neuropathological conditions such as multiple sclerosis, AIDS, childhood lead poisoning and perhaps even Alzheimer’s.

You’ll have to use your imagination with this diagram–the blue cells are the cells of a capillary wall. Tight junctions form a seal between the cells of the capillary wall and keep all the riffraff in the blood out of the nearby nervous system.

So if your blood-brain barrier is working today, give it three cheers. It’s a silent but vital friend. Brake for blood-brain barriers—after all, most things all ready do.

Welcome to Pop Synaptics!

So you’re interested in Neuroscience. You’ve come to the right place. The brain has been called The Last Frontier, and Pop Synaptics can be your covered wagon for the trail, your Santa Maria to the ocean of cognitive functioning, your Apollo 11 to the moon of the nervous system–am I being overly dramatic? Probably. But despite my histrionics, it’s true that in many ways the brain and really the whole study of neural structure and functioning (which we call Neuroscience) is one of the most dramatic, romantic and mysterious scientific pursuits of today. Few other fields of study are so inescapable—our neural functioning is the framework of our identities, our activities, our relationships, our desires, even, some might say, our souls. There is a vast unknown residing right here inside our bodies and minds, and we want to know more about how we know, to ponder how and why it is we think.  It’s science mixed with metacognitive poetry, and it’s enchanting.

But while our brains and nervous systems are intrinsic, the study of them is often inaccessible. Try to sift through the latest brain-breakthroughs without a PhD or two and you’ll be facing some major cranial cramps. That’s why I’m starting Pop Synaptics—to give those who are interested in the field of Neuroscience a foundation in the field, no matter what they keep as their day job. Think of Pop Synaptics as a survey course with a lot more kick-ass, a blogger’s smorgasbord of the fundamentals and highlights of Neuroscience.  You don’t need to be a trained scientist to learn from and enjoy Pop Synaptics, although I hope that scientists will enjoy this blog alongside beauticians, landscapers, engineers, students and anyone else who simply possesses an interest in the workings of the brain and nervous systems. Because many of the blogs all ready on the web focus primarily on Neuropsychology or take a complex, technical approach to Neurobiology, Pop Synaptics will focus mostly on making Neurobiology fun and easy to understand while incorporating elements from her sister study of Neuropsychology from time to time. As we move through the field of Neuroscience together, I’ll try to bring you a mixture of the newest, coolest breakthroughs as well as basic tenets of Neuroscience. Above all, my goal is to make Pop Synaptics fun and understandable because in the end, the last frontier should be open to anyone who wants to make the trek.