Showing posts tagged brains

SICK PAPES SPECIAL ON CONTROVERSY: PART 2

Curr Biol. 2010 Sep 14;20(17):1534-8.
The role of the magnetite-based receptors in the beak in pigeon homing.
Wiltschko R, Schiffner I, Fuhrmann P, Wiltschko W.

VERSUS

Nature. 2009 Oct 29;461(7268):1274-7.
Visual but not trigeminal mediation of magnetic compass information in a migratory bird.
Zapka M, Heyers D, Hein CM, Engels S, Schneider NL, Hans J, Weiler S, Dreyer D, Kishkinev D, Wild JM, Mouritsen H.

AND

Nature. 2012 Apr 11;484(7394):367-70.
Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons.
Treiber CD, Salzer MC, Riegler J, Edelman N, Sugar C, Breuss M, Pichler P, Cadiou H, Saunders M, Lythgoe M, Shaw J, Keays DA.

There are some scientific subjects that attract recreational bedlamites like seagulls to a coastal landfill. My favorite of these is magnetoreception: the ability of an animal to perceive an ambient magnetic field. Lots of animals can do this—birds, insects, reptiles— and some of them use the earth’s weak magnetic asymmetry to achieve extraordinary feats of navigation. For example, scientific hero Ken Lohmann has shown that sea turtles navigate thousands of miles through the horrific salty ocean in order to meet their half-shelled-brethren at a specific location for an annual Bacchanalian picnic. Ken’s lab also found that if you move a spiny lobster 20 miles in any direction from its preferred hangout spot, it immediately returns directly to its headquarters using cues from the earth’s magnetic field. These and bajillions of other examples demonstrate that many of the earth’s macro-biotic inhabitants can use a magnetic sense to cruise around in magnificent style, which, in my humble opinion, is absolutely fucking fantastic.

Returning to the bedlamites. There are two dudes in particular that illustrate the fact that magnets exert a certain ineffable force upon the zanier castes of our super-organismic civilization. The first of these is shown in the video above: Mr. Harry Magnet, whose extensive pape on personal perception of magnetic fields cannot be deemed sick or otherwise, because it has not undergone rigorous peer review (but we welcome submissions).

The second example comes from Alane Jackson, the purveyor of a theory called magnetrition, which was first explained to me by a youth soccer referee who lived in a wigwam on an magnetically neutral island in the middle of an Alaskan lake. Basically, Alane’s idea is that mitochondria are magnetically charged, and that jostling our cells around causes cytoplasmic stirring, thereby promoting health. I also recommend another section of Alane’s website, titled Smoking is good.

Buried beneath all of this absolutely essential HTML is an equally intense scientific debate about the mechanisms by which real animals measure magnetic fields. So far, two basic mechanisms have been proposed:

(1) MAGNETITE. The magnetite hypothesis was inspired by the observation that some magnet-loving bacteria produce magnetite (Fe3O4) crystals that cause them to align with and cruise along the local magnetic vibe. Because magnetite has also been found in the snouts/beaks of fish and birds, it was suggested that the rotation of these crystals could be detected by mechanosensory neurons in the brain. Smaller, “superparamagnetic crystals” have also been found in bird beaks. These crystals do not have a permanent magnetic moment, and therefore do not individually rotate to align with the earth’s magnetic field. However, large arrays of these superparamagnetic crystals would attract and repulse each other under different magnetic field conditions, generating forces that could, in principle, be sensed by neurons.

(2) CRYPTOCHROME. This second mechanism is even bonkers-er. Some radical-pair chemical reactions can be influenced by magnetic forces—one example is the absorption of light by retinal photopigments called cryptochromes. The idea is that the ambient magnetic field would alter the rate of cryptochrome photo-isomerization, so that if a bird were gazing upward at a clear blue sky, it could actually “see” a hazy magnetic field image layered on top of the normal visual scene.

The argument surrounding these two mechanisms is best exemplified in the bird magnetoreception literature, which has been enriched in recent years by a flurry of combative pape-slinging. In one camp, (1) the Wiltschkos and their pals claim that birds use little magnetite particles in their beaks to detect magnetic fields, while in another camp (2) Henrik Mouritsen and his pals  claim that magnetoreception arises in the retina, mostly likely through cyptochrome. (3) David Anthony Keays and his buds weighed in on side 2 of the fracas last year, when they suggested that those magnetite particles in the beak are located inside little pieces of biological irrelevance called macrophages.

Although the field of magnetoreception is confusing and controversial, one cannot help but delight in the titillation-level of the questions and the unfettered academic shit-hurling. Magnetoreception is clearly the modern El Dorado, attracting both well-funded academics and itinerant kooks. There is the important possibility that everybody is right— that birds have two independent magnetic senses and so do people, and the booty will be split evenly amongst the Professors and the online gurus. It seems much more likely to me, however, that this entire field is booby-trapped, and that all the magnet-lovers will end up stalking monkeys on a raft as the river below their feet slowly transforms into a cauldron of boiling soup.

Contributed by butthill

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Eliasmith, C., Stewart, T., Choo, X., Bekolay, T., DeWolf, T., Tang, Y., & Rasmussen, D. (2012). A Large-Scale Model of the Functioning Brain Science, 338 (6111), 1202-1205 DOI: 10.1126/science.1225266

The H. P. Lovecraft novella At the Mountains of Madness is a story about scientific hubris, and the insignificance of human achievement when confronted with the vastness that is the cosmos. The central characters are scientists searching the Antarctic for novel geological or biological forms. They uncover a world of strange, ancient beings, seemingly preserved in the ice. Their discovery has profound implications for the nature of biological evolution, and perhaps the history — and future — of earth itself. The primary entity they find is a god-like tentacled, winged, gilled monstrosity with strange geometrical features. We are given this account:

“It had digestion and circulation, and eliminated waste matter through the reddish tubes of its starfish-shaped base … The nervous system was so complex and highly developed as to leave [the scientist] aghast. Though excessively primitive and archaic in some responses, the thing had a set of ganglial centers and connectives arguing the very extremes of specialized development. Its five-lobed brain was surprisingly advance and there were signs of a sensory equipment, served in part through the wiry cilia of the head, involving facts alien to any other terrestrial organism … It was partly vegetable, but had three-fourths of the essentials of animal structure.”

I had a similar reaction when reading about S.P.A.U.N., the monstrous creation described by Eliasmith et al. in their pape: “A large-scale model of the functioning brain”. The title alone suggests a new and scary precipice of human achievement. And a most sick pape. 

S.P.A.U.N. is half way between a robot and a computer program. It has a small camera attached to its head, and a robotic appendage extending from an implied torso that is capable of drawing all manner of digits between 0 and 9. Its brain has multiple sub-systems that independently control the encoding of visual input, reward, working memory, decoding, and motor output. The thrust of Eliasmith et al.’s pape is not that any one component of S.P.A.U.N. is new, but that it can perform not just one task but a variety of tasks, all of which humans can perform, and that its modular architecture resembles and realistically models at least some aspects of the human brain. 

How close does S.P.A.U.N. come to resembling the brain? Each of its systems are meant to correspond to cortical and sub-cortical brain areas or functions, though much of the correspondence seems superficial. For example, S.P.A.U.N. has a system for handling “Visual Input”. It’s implied that it corresponds to areas V1, V2, V4, and IT of the primate visual pathway. But S.P.A.U.N. cannot mimic known processing in all those areas because we still don’t know what they do! The visual system of S.P.A.U.N. also reveals that its individual neurons are not as realistic as you might think. The authors stress that it uses biologically-realistic neurons with neurotransmitter dynamics, but most of the visual system instead uses simple linear combinations and thresholding. It’s hard to evaluate these shortcuts because the system is so complex.

So S.P.A.U.N. can do some cool tricks and kind of maybe looks like a brain. Can it fight a bear in one-on-one combat? Definitely not. S.P.A.U.N.‘s proponents admit that it is not the most impressive robot. When I googled “what is the sweetest robot?” I found this strawberry-picking robot. It uses 3D image processing to evaluate ripeness, and can delicately pluck luscious plump strawberries from their stems. That seems more impressive than S.P.A.U.N.

Becoming the best robot is not S.P.A.U.N.’s goal. What is the goal? Building AI systems that perform complex, physical, interactive tasks with flexible, modular systems resembling known biology, that could in principle help us understand how brains work. A longstanding, and recently popularized but criticized, tradition in AI is to build systems that have vast representational power, memory, and fancy statistical learning algorithms, but generally produce simple outputs. For example, a computer vision system that encodes a complex image but only needs to decide which of 10 different kinds of objects it is looking at. But most animals evolved to do more than spit out a 10-bit vector. They engage in real-time with a dynamically changing world. S.P.A.U.N.’s complex motor output and working memory is a step forward, but its emphasis on symbolic reasoning — which number comes next in a sequence? — is excessively abstract. If such symbolic reasoning evolved as an abstraction of more directly-physically-realized functions — when can I jump to make sure I catch the next mouse? — why not first try to build robots that can accomplish those tasks? I recommend the exciting research program of the “embodied robotocist” Rodney Brooks, especially his efforts in the 1990s to build robots with distributed control systems for path finding and navigation. He also appears, looking entirely crazed, in this movie, which features robots, lion taming, tree grooming, and naked mole rats. We are truly standing beneath the Mountains of Madness.

Contributed by istudyvision
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