Kris Carlson

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My favorite passage by Dave Waltz

Dave Waltz was a friend and a mentor. He passed away in March 2012 from a glioblastoma. There was a wonderful symposium in his honor held over the weekend at Brandeis University and ably organized by Prof. Jordan Pollack. I send the following excerpt from Dave’s writings to a few friends who knew him last week.

…I dispute the heuristic search metaphor, the relationship between physical symbol systems and human cognition, and the nature and “granularity” of the units of thought. The physical symbol system hypothesis, also long shared by AI researchers, is that a vocabulary close to natural language (English, for example, perhaps supplemented by previously unnamed categories and concepts) would be sufficient to express all concepts that eve need to be expressed. My belief is that natural-language-like terms are, for some concepts, hopelessly coarse and vague, and that much finer, “subsymbolic” distinctions must be made, especially for encoding sensory inputs. At the same time, some mental units (for example, whole situations or events—often remembered as mental images) seem to be important carriers of meaning that may not be reducible to tractable structure of words or wordlike entities. Even worse, I believe that words are not in any case carriers of complete meanings but are instead more like index terms or cues that a speaker uses to induce e listener to extract shared memories and knowledge. The degree of detail and number of units needed to express the speaker’s knowledge and intent and the hearer’s understanding are vastly greater than the number of words used to communicate. In this sense language may be like the game of charades: the speaker transmits relatively little, and the listener generates understanding through the synthesis of the memory  items evoked by the speaker’s clues. Similarly, I believe that the words that seem widely characteristic of human streams of consciousness do not themselves constitute thought; rather, they represent a projection of our thoughts onto our speech-production faculties. Thus, for example, we may feel happy or embarrassed without ever forming those words, or we may solve a problem by imagining a diagram without words or with far too few words to specify the diagram.

Waltz, David L., The Prospects for Building Truly Intelligent Machines, Proceedings of the American Academy of Arts and Sciences (Daedalus, Winter 1988), V 117 N 1, pg 197.

September 24, 2012 Posted by | Artificial Intelligence, Neuroscience | Leave a comment

Tumor-treating fields for glioblastoma and lung cancer

I have recently lost a friend, Dave Waltz, to glioblastoma, and a few years ago lost a friend of our family, Colby Hewitt, to the same cancer. Tumor-treating fields (TTF) have brought to fruition the ingenious idea of Dr. Yoram Palti to use alternating electric fields to disrupt the delicate orchestration of mitotic spindle formation during cell divisions. So the fast-growing cells in the brain, i.e. the cancer cells, are the ones affected, and since most other cells in the brain either do not reproduce or do so slowly, normal brain function is not disrupted in the period of treatment time.

There are several types of ions involved in mitotic spindle formation, including the spindle, helper cells that form the spindle, and the chromosomes. TTF could affect one or more of these necessary participants.

According to the company, the disruption of cell division leads to apoptotis (programmed cell death) of the cancer cells–i.e. I gather other cell processes designed to be trigger apoptosis when abnormalities are detected are signaled by the inability of the cell to complete spindle formation.

Here is the overview from the company, Novocure, a key paper, and an excellent, lucid exposition of the physics underlying TTF.

Kirson et al-Alternating electric fields arrest cell proliferation in animal models and human brain tumors-PNAS-2007.pdf

Jones-Basic theory of dielectrophoresis and electrorotation-IEEE EngMedMag2003.pdf


May 28, 2012 Posted by | CNS Disorders, Disease and Disorder, Neuroscience | , , , , , | Leave a comment

Ramon y Cajal on the Love of science

In a book Advice for a Young Investigator Cajal wrote: “As with the lover who discovers new perfections every day in the woman he adores, he who studies an object with an endless sense of pleasure finally discerns interesting details and unusual properties…. It is not without reason that all great observers are skillful at drawing.”

–In Nerve Endings: The Discovery of the Synapse by Richard Rapport, a biography of Santiago Ramon y Cajal (1852-1934), pioneering neural anatomist. Quoted by frequent MathGroup (Mathematica) participant, David Park.

September 29, 2010 Posted by | History of Science, Neuroscience | , , | Leave a comment

Lateral Inhibition from Dictionary of Biological Psychology

lateral inhibition: A feature of RECEPTIVE FIELD organization in SENSORY NEURONS and in other neural systems whereby signals from a RECEPTOR in one region can be inhibited by those from surrounding regions. This causes the neuron to be strongly activated by contrast difference between nearby regions but only weakly by uniform stimulation, giving an efficient sensory code which emphasizes significant stimuli. Lateral inhibition has been most studied in the eyes of arthropods for example LIMULUS and in mammalian retinal ganglion cells see RETINAL CELL LAYERS but it is also an important feature in AUDITORY PERCEPTION and somatosensation.

See also: contrast sensitivity; pattern perception; retina


via Lateral Inhibition from Dictionary of Biological Psychology.

February 20, 2010 Posted by | Neuroscience | 1 Comment

Los Alamos National Laboratory LANL: Roadrunner supercomputer puts research at a new scale

World’s fastest supercomputer, 10^15 ops/second, cost $120M, as of 6/12/2008:

On Monday scientists used PetaVision to reach a new computing performance record of 1.144 petaflop/s. The achievement throws open the door to eventually achieving human-like cognitive performance in electronic computers.

Based on the results of PetaVision’s inaugural trials, Los Alamos researchers believe they can study in real time the entire human visual cortex—arguably a human being’s most important sensory apparatus.

PetaVision models the human visual system—mimicking more than 1 billion visual neurons and trillions of synapses.

Because there are about a quadrillion synapses in the human brain, human cognition is a petaflop/s computational problem.

The Roadrunner is the world’s first supercomputer to achieve sustained operating performance speeds of one petaflop/s. In partnership with Los Alamos and the National Nuclear Security Administration, Roadrunner was built by IBM and will be housed at Los Alamos National Laboratory, where it will be used to perform calculations that will vastly improve the nation’s ability to certify that the United States nuclear weapons stockpile is reliable without conducting underground nuclear tests.

Roadrunner was built using commercially available hardware, including aspects of commercial game console technologies. Roadrunner has a unique hybrid design comprised of nodes containing two AMD OpteronTM dual-core processors plus four PowerXCell 8iTM processors used as computational accelerators. The accelerators are a special IBM-developed variant of the Cell processors used in the Sony PlayStation® 3. Roadrunner uses a Linux operating system. The project’s total cost is approximately $120 million.

Los Alamos National Laboratory LANL: Roadrunner supercomputer puts research at a new scale.

December 6, 2009 Posted by | Neuroscience | , , | Leave a comment

Is the Calyx of Held a Fail-Safe Synapse?

Describes two sets of experiments to see whether the large, bulbous calyx of Held is a true “fail-safe” synaptic structure that always fires, or not, and the evolutionary reasoning behind either case.

Synapse #fail, Science #win « Building Blogs of Science.

November 25, 2009 Posted by | Neuroscience | Leave a comment

Is the inconsistent firing of sensory neurons a bug or a feature?

Carnegie Mellon Scientists Develop Method To Make Cortical Neuronal Firing More Efficient.

Carnegie Mellon University biologists have found that firing reliability in the cerebral cortex can be significantly improved through pattern sensory activation, indicating that this unreliability isn’t a necessary component for cortical function. The researchers, led by Alison Barth, believe the discovery will become a cornerstone for furthering future research on brain functioning and perception. The study was published in the Sept. 23 issue of the Journal of Neuroscience.

Alison Barth, associate professor of biological sciences.

“One of the most mysterious features of the cortex is how bad it is at transmitting information,” said Barth, associate professor of biological sciences and a member of the Center for the Neural Basis of Cognition. “The cerebral cortex on a cell-to-cell basis tolerates great unreliability and impreciseness, yet still manages to function. This led us to ask, is this a bug or a feature?”

The Carnegie Mellon researchers sought to find out if this inefficiency was a feature of the wiring of the cerebral cortex. They believed that if the unreliability were indeed a feature, the variability in firing rates would be difficult to alter. The researchers tracked the neurons’ plasticity, or their ability to change, to tactile information in the cerebral cortex in a humble laboratory mouse. To induce plasticity, the investigators designed an experiment in which the mouse senses its surroundings through only one whisker. Whiskers are useful in studying neuronal plasticity because, like human fingers, each whisker is linked to its own unique area of the brain’s cortex, making it easy to monitor activity and changes in a single neuron in the correct region of the cerebral cortex.

Barth and colleagues found that, over time, animals that sensed the world through only one whisker showed a doubling in neuronal firing rates, with the frequency and timing of response much more reliable and precise. Improvements look longer to occur in older mice, but were still seen. These results indicated to the researchers that inefficiency in neuronal firing in the cerebral cortex could be easily corrected through repeated stimulation, indicating that it is not a fixed or necessary feature of the brain’s circuitry.

According to Barth, the next step will be to investigate the molecular mechanisms behind cortical neuronal firing and what impact they have on perception.

“The brain is the most marvelous computer that has been conceived of and it works so well as a whole, even with sub-par pieces. We need to find how it can function given what appears to be rather shoddy components,” Barth said.

The results will enable researchers to focus on the precise molecular mechanisms that underlie changes in neuronal reliability. In addition, they will help computational neuroscientists devise more accurate models of cortical function. Barth hopes to be able to directly address the role of precise firing in improved perception, using tactile stimulation delivered through the mouse’s whiskers. “More reliable firing should mean that the animal can sense things that previously were undetectable,” she said. “And if we can make the system work better, the fascinating question still remains: why isn’t it optimized to do this in the first place?”

October 20, 2009 Posted by | Neuroscience | Leave a comment

Discovery in cognitive linguistics

“We showed that distinct linguistic processes are computed within small regions of Brocas area, separated in time and partially overlapping in space,” said Sahin. Specifically, the researchers found patterns of neuronal activity indicating lexical, grammatical and articulatory computations at roughly 200, 320 and 450 milliseconds after the target word was presented. These patterns were identical across nouns and verbs and consistent across patients.

October 17, 2009 Posted by | Neuroscience | Leave a comment


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