Tuesday, May 11, 2010

About Us & Other Minds

Recently, the possible existence of extraterrestrial intelligence has been much discussed in the media. The eminent cosmologist Stephen Hawking weighed in on his Discovery Channel Show entitled "Stephen Hawking's Universe" with a dramatization (see also msnbc post entitled "Hawking: Aliens may pose risks to Earth" dated Apr. 25, 2010). Perhaps, the interest is related to the discovery of ever more exoplanets. According to the Extrasolar Planets Encyclopaedia, the number of exoplanets currently stands at 452. It is only a question of time that a planet is discovered that may be similar to Earth, increasing the chances for alien intelligence to exist.

No doubt, alien minds are difficult to fathom. I once had the privilege to visit the Yerkes National Research Primate Center in Atlanta. I remember this visit vividly, because I had my first close encounter with chimpanzees. The settings are like in a zoo. We were urged to don protective gear. Though we kept a distance to the monkeys of perhaps ten yards, the usefulness of the garb quickly became obvious. Some chimpanzees lived in groups and behaved a bit like a neighborhood gang when a new kid turns up on the block. They eyeballed us with curiosity. They tried to garner our attention with posturing and acting out, producing an incredible racket. They immediately probed who was in charge. If you took your eyes off them for a second, they would spit at you, running away overjoyed when they landed a hit. We discovered quickly that chimpanzees command four hands. One young male was beating on a drum with his upper extremities. While we got distracted by his banging, he aimed pieces of feces at us using his foot with great accuracy. The band howled in pure joy. We were soiled and quite intimidated. We felt that without a fence they would outsmart us and, if they wanted to harm us, we would not stand a chance unarmed.

In another encounter, we approached a compound with two occupants. The monkeys were sitting high up on logs, biding their time, contemplating. We stood silently and watched. They watched us. I habitually scratch my head when I wonder. One monkey gazed at me with eyes like gleaming coal for what seemed an eternity. Her composure had a deep inquisitive, almost wise quality, as if she was questioning me, " who are you? What do you want from me?" She scratched her head.

I walked away from this encounter moved. The chimpanzees seemed so much like us. Yet, they were so different. I was wondering whether we shall ever be able to figure out the mind of a chimpanzee, let alone other species that appear to radiate a similar intelligence, but are even more removed from us. Will we be ever be able to understand the mind of a whale? I remain unsure.

However, I believe that though we may not be able to understand these creatures, we can learn a lot from them and should treat alien minds with respect.


  • Dimitar Sasselov estimates that one hundred million exoplanets in the Milky Way may support life similar to Earth. Watch his talk at TED2010 entitled "How we found hundreds of Earth-like planets" below (07/21/10):
  • Claudia Dreifus conducted an informative interview with Diana Reiss who studies dolphin behavior. Professor Reiss elaborates on experiments she and colleagues conducted, demonstrating that dolphins recognize themselves in mirrors. The interview with the title "Studying the Big-Brained Dolphin" was published online in The New York Times today (09/20/10).
  • The CNN video below shows an instructive demonstration of the dolphins' ability of imitating behavior, no simple feat. Rizzolatti and Sinigaglia (2008) suggest in their book entitled "Mirrors in the Brain" that imitating the others is the first step to empathy (01/14/11):

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Wednesday, May 5, 2010

Force & Resilience

Yesterday, I watched NOVA's premiere on PBS with the title "MT ST HELENS BACK FROM THE DEAD". The show informs us about insights gained from thirty years of examination of Mount St. Helens and its surroundings, after the volcano blew out its top and one entire side in a massive explosion on May 18, 1980.

The footage of the eruption is breath-taking. The destructive forces unleashed in the catastrophic blast are incomprehensible. Pyroclastic flows wiped out life over 230 square miles. But I was most impressed, following in time-lapse life bounce back in this alien, primordial landscape of utter destruction and desolation. After three months life returned.  A tiny whiskered rodent the size of a hamster, the Northern Pocket Gopher Thomomys talpoides, had survived in its burrows, and even in the most devastated pumice zone, nitrogen-fixating lupines began to flourish. On the surface things seem to progress astonishingly well.

By contrast, underground the outlook is different. Though we have learned much about the forces driving the mountain's eruptions, the interviews with geologists on NOVA make clear that we understand little about the rhythms of seismic activity under the volcano, rendering accurate risk assessment and reliable prediction of a major eruption virtually impossible. I remember watching the last period of noticeable volcanic activity five years ago. I witnessed a dome grow inside the crater and lava glow at night. Ever since, the volcano appears ostensibly quiet.

Despite this respite, the show urgently reminds us of the need to keep a close eye on the mountain. The behavior of burrowing animals with a highly developed sense of touch may provide signatures that may help warn us of a major impending seismic event (see related posts). It may be instructive to observe Northern Pocket gophers. I periodically check the U.S. Forest Service's volcanocam, the least because on some days, weather willing, the mountain looks magnificent and I love to watch the seasons change on her:

  • Dmitrieva and others (2013) report that sustained ground vibrations between 0.5 and 5 Hz, known as seismic tremor, have been observed to precede explosive volcanic eruptions by 30 s. Rodent whiskers are particularly sensitive in this range (see my post with the title "The Quest for the Infrasound Acoustic Fovea" published Oct. 12, 2009). The gophers in the pumice zone of Mt. St. Helens may have been saved by sensing this early warning. Ira Flatow interviewed a co-author of the study in the broadcast segment entitled "Volcano 'Screams' Before Eruption" on National Public Radio's Science Friday yesterday (07/20/2013).

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Saturday, May 1, 2010

The Beautiful Eimer's Organ

Maikäfer by H. Baluschek
May is the season of the Maikäfer in Germany, and moles become most active. Hence, in this month we celebrate Gustav Heinrich Theodor Eimer's arguably greatest discovery. Even Frau von Welt discussed it, though in fleeting. Theodor Eimer was born in Zürich, Switzerland, on Feb. 22, 1843, and passed away on May 29, 1898, in Tübingen, Southern Germany. His biography remains scant. After an extended search, I gleaned his birthday from the simple plaque on his grave pictured in this tour of Tübingen's Bergfriedhof. Plaque is a misnomer here. It consists of a rectangular steel plate with black lettering painted on gray rust-proofing. The simplicity does not come close to reflect his discovery.

Theodor Eimer aspired a career in comparative zoology and anatomy. He spent his junior faculty years as prosector at Julius-Maximillian's University, Würzburg, Germany, and moved on to hold a chair in zoology at Eberhard-Karl's University, Tübingen, where he led a productive life as an evolutionary biologist, struggling with Darwin's theory until his untimely death at the age of 55. His greatest scientific contribution, however, may have been as an early neuroethologist. Perhaps, it is this contribution that helped Tübingen's university and its three affiliated Max Planck Institutes develop into a hotbed of neuroscience today.

During his tenure in Würzburg, Theodor Eimer became the first to describe the discrete microscopic organ of touch that densely populates the tip of the nose of the European mole Talpia europaea. The organ is named in his honor. In his original publication (Eimer, 1871), he examined in great detail the structure of the nose, the distribution of the touch organs on the nasal skin, and the relationship of their density with the nose's use for palpation. Eimer sought to establish a connection between structure and function.

Eimer's organ fascinated me, ever since I saw one under the microscope in histological preparations Kenneth Catania showed me. Kenny is studying the North American star-nosed mole Condylura cristata. He counted roughly 25,000 Eimer's organs on these moles' nose appendages called rays. The organ consists of a minute skin papilla between a tenth and a fifth of a millimeter in diameter. At the papilla's core, a beautifully geometric constellation of nerve fibers with free endings is embedded with great symmetry in a conspicuous column of epithelial cells. Eimer (1871) saw two to three single nerve fibers, rising strait in the middle of the column and ending in the fifth layer under the stratum corneum that forms the hard top of the epidermis. The fibers extend short protrusions perpendicularly into each epithelial layer they traverse, where the protrusions end in 'buttons'. They are ringed by a circle of roughly 19 evenly-spaced nerve fibers, known as satellite fibers, whose protrusions point inwards. In addition, Eimer (1871) distinguished a separate set of nerve fibers with free nerve endings. By contrast to the fibers in the papilla's core, these travel obliquely toward the surface at the papilla's perimeter. Both sets are illustrated in his Fig. 2 of his 1871 publication, partially reproduced below:

His legend to this figure reads: Longitudinal section through the frontal surface of the mole's snout treated with the Gold-method. T touch cone, N nerve bundle, E epithelium, C corneum, magnification 400/1.

With improved histological techniques, a second touch receptor type, Merkel cell-neurite complexes, was found in the stratum germinativum at the bottom of the epidermis (darkest part in Eimer's figure), and a third, lamellated corpuscles of Vater and Pacini, was discovered in the stratum papillare of the dermis (white in Eimer's figure) underneath the Merkel cells (Halata, 1975).

Today, we still do not understand precisely how these receptors transduce touch into the electrical signals that the nerve fibers transmit to the brain. But we have learned much about the properties of touch, e.g. frequency and force, to which the receptors respond and how their responsiveness changes with prolonged stimulation. The receptors can be functionally distinguished based on these features. The nerve fibers with free nerve endings and the nerve fibers ending on Merkel cells adapt their responses to touch rapidly, whereas the nerve fibers ending in the lamellated corpuscles are considered slowly adapting.

Marasco and others (2006) were able to attribute different functions to Eimer's two sets of free-ending nerve fibers in the star-nosed mole and the coast mole Scapanus orarius. The authors furnish outstanding micrographs of the organ and its innervation, depicting Eimer's free-ending fibers as well as the Merkel cell-neurite complexes and the Vater-Pacini corpuscles. Using a histochemical marker for a protein known to be involved in the processing of pain, they were able to label the nerve fibers at the perimeter of the papilla, suggesting that they are nociceptive. That is, they respond to pain. By contrast, the fibers in papilla's core did not stain for the protein, suggesting that they are mechanoreceptive. These nerve fibers as well as the Merkel cell-neurite complexes are known to respond to local touches with great sensitivity, whereas the Vater-Pacini corpuscles are highly tuned to the frequencies of dispersed vibrations. Eimer's organ, therefore, forms a receptor complex, integrating pain receptors as well as three fundamentally different types of touch receptors which preferentially respond to either skin indentations or vibrations. The follicles of whiskers, also known as vibrissae or sinus hairs, and the push rods in monotremes (Proske and others, 1998) represent the only other known discrete structures in the skin that combine three mechanoreceptor types.

The Eimer's organs on the nose may be the mole's main tool with which the animal can capture a refined picture of its underworld.  Catania and Kaas (1995) have shown that the nose of the star-nosed mole is mapped in multiple topographic representations on an extraordinarily large swath of cerebral cortex that processes touch. Discrete morphological modules of nerve cells that are clearly discernible in histologically stained sections represent each ray in the same order as they surround the nose. This topographic morphological representation of the sensory periphery is similar to that of the facial whiskers by cytoarchitectonic modules called barrels in the rodent cerebral cortex. I touched on whiskers and barrels in my posts dated Oct. 12, 2009, and Dec. 24,  2008.

To date, two complete cortical maps of the nose with its rays have been found in the brain of the star-nosed mole. There may be more. The nose's disproportionate representation in cerebral cortex is suggestive of a fovea for nose touch in the mole's somatic sensory system (Catania, 1995).

Already Professor Eimer recognized the importance of the mole's nose to the behavior of the species. He begins the introduction to his 1871 publication with the statement: "The mole's snout must be the seat of an extraordinarily well developed sense of touch, because it replaces almost entirely the animal's sense of face, constituting its only guide on its paths underground." He estimated that the nose of the European mole was covered with more than 5,000 Eimer's organs which were invested with 105,000 nerve fibers. He took the abundance of sensory innervation to affirm his contention that the nose's touch must represent the moles dominant facial sense. Professor Eimer ends his report with the assertion that his interpretation is entirely consistent with the common knowledge of his time. His last sentence reads: “This enormous richness of innervation easily explains the well-known fact that already a light blow to the snout kills the mole instantly.”

Roughly 130 years after Professor Eimer's discovery, Catania and colleagues accomplished to record striking behavioral evidence in favor of his conclusion, using a high-speed camera that the eminent professor could hardly have imagined  (Catania and Remple, 2004).  Professor Eimer would have been fascinated, watching this footage. Moles with the help of their Eimer's organs may be perfectly poised to detect seismic vibrations.

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Impressively shown by the two Reuters news clips below, high-speed video cameras have developed into invaluable tools in the study of animal behavior. Their application range from the examination of bat flight
to feline drinking, providing new insights propelling engineering design (11/12/10).