This week: a lot of brain stuff as usual, this time centered around the effects of choline, tryptophane and carbohydrates in the food, some theoretical computation and some bad news from general relativity.
A brain interface Pre- and neonatal choline improves memory and reactions among rats Mozart doesn't make monkeys smarter Bacterial growth in space Low tryptophan levels can impair memory and mood Carbohydrates in the food can be good for your mood Using the continuum to compute noncomputable numbers A quantum dot neural network Topological censorship - bad news for spacetime engineers The Wind from the Sun
Restoration of neural output from a paralyzed patient by a direct
P. R. Kennedy and R. A. Bakay
Neuroreport 9:8 1707-11 Jun 1 1998
The authors describe a communications link for a "locked-in" patient with ALS. It consisted of a hollow glass cone, with gold recording wires. Before implantation the cone was filled with neurotrophic factors, encouraging neurons to grow into it and make connections; this takes around 3 months and produce stable recordings at least for 15 months (in monkeys). The electrode was implanted in the motor cortex, and the patient could learn to control the signal so that it acted as a binary switch. This system with neurotrophic factors (or even implanted peripheral nerves) looks a bit like the future, expecially since it seems to survive well.
Perinatal choline supplementation increases the threshold for chunking
in spatial memory
W. H. Meck and C. L. Williams
Neuroreport 8:14 3053-9 Sep 29 1997
Characterization of the facilitative effects of perinatal choline
supplementation on timing and temporal memory
W. H. Meck and C. L. Williams
Neuroreport 8:13 2831-5, Sep 8 1997
One of the most fascinating forms of memory enhancement occurs when choline is given to pregnant rats during day 12-17 of pregnancy and/or to the pups at postnatal day 15-30. This results in what appears to be a permanently better memory. In these two papers Meck and Williams study how much treated and untreated rats chunk their memories, and how well they can time their responses. In the chunking study, they studied how the rats organized their food gathering in a maze. It turned out that treated rats were better at gathering food (as expected) and also that they started to chunk memories (i.e. first take all the cocoa puffs, then the seeds, then the pellets instead of just taking them in a radom order) later than the ordinary rats when the maze was made more complex and demanding. That suggests that they had better working memories. In the timing study the rats were to respond after 20 seconds, and the choline treated rats managed that task with less variance than the untreated. When given nicotine, which increases the subjective clock so they respond prematurely, the choline treated rats reacted more strongly than the untreated ones. To sum up, choline supplementation seems to enhance spatial and working memory as well as time memory for rats. It is interesting to wonder what the effects might be in humans.
Effects of music and white noise on working memory performance in monkeys S. Carlson, P. Rama, D. Artchakov and I. Linnankoski Neuroreport 8:13, 2853--6, Sep 8 1997
It has been claimed that listening to Mozart improves cognitive
performance. One suggested explanation has been that the music sets up
some kind of rhytm or entrainment in the brain that is
beneficial. This study tested this by using monkeys as experimental
subjects instead of students as usual. The monkeys had learned to do a
working memory task, and silence, music (Mozart's Piano Concerto
No. 21 in C), a simple rhythm and white noise was played for the
monkeys before or during testing. If the sounds were played before
there was no significant effect. If played during the task Mozart
*decreased* their performance, while white noise increased it
(compared to the silence control group). This suggests that whatever
the beneficial effects of music are in humans, they are not due to some simple neurologic effect but rather our higher level cognition. For the monkeys the complex music was just distracting. White noise might be a good way of tuning out other distractions; this may be why some people work better when it rains.
Bacterial growth in space flight: logistic growth curve parameters for
Escherichia coli and Bacillus subtilis
M.A. Kacena, G.A. Merrell, B. Manfredi, E.E. Smith, D.M. Klaus and P. Todd Appl Microbiol Biotechnol, 51:229-234 1999
Perhaps a potential problem one day: bacteria cultures appear to grow more quickly in space than on Earth. In this paper the authors studied the logistic growth of bacteria and compated them to similar experiments on the ground, and it looks like bacteria can grow to higher stationary state concentrations and have shorter lag-times, most likely because they can fully exploit three dimensions and do not sediment. Better clean more often in space.
Tryptophan depletion in normal volunteers produces selective
impairment in memory consolidation
Wim J. Riedel, Tineke Klaasen, Nicolaas E.P. Deutz, Astrid van Someren and Herman M. van Praag
Psychopharmacology 141: 362--369 1999
The effects of tryptophan depletion and loading on laboratory
aggression in men: time course and a food restricted-control
James M. Bjork, Donald M. Dougherty, F. Gerald Moeller, Don R. Cherek
and Alan C. Swann
Psychopharmacology 142: 24--30 1999
Serotonin is involved in cognitive performance such as learning and
memory, and also in the regulation of mood. The amino acid tryptophan
is used to produce serotonin, and by manipulating the levels in the
blood the serotonin levels can apparently be influenced. These two
articles study what happens when test subjects are given food or drink
that depletes or increase the levels of tryptophan. The first article
found that the subjects given an amino acid mixture without tryptophan
(which causes the levels to decrease by competition) suffered a
decrease in memory consolidation, but not on working memory, perception, attention and executive functions. In the second study participants were given drinks that either decreased or increased tryptophan levels, and their aggressiveness was studied (by measuring how often they tried to retaliate against a (simulated) participant who caused them loss of money in a game). Men with low tryptophan levels became more aggressive, while raised tryptophan levels didn't make them more peaceful than when tested on an empty stomach. So tryptophan depletion looks like something best avoided, although tryptophan supplementation might not make us much more peaceful (the cognitive effects are another question).
Can you control your mood with carbohydrates?
Value of pleasures and Questions of Guilt Workshop 1997 http://www.arise.org/bentab2.html
(There are more fun papers on that website about pleasure, I will
likely review more of them in the future).
A nice review of the literature of the effects of carbohydrates on mood. It turns out that the interactions are fairly tricky, since they involve both the insulin response and other factors. A feeling of less energy and more relaxation develops around two hours after a meal, but drinking a high sugar drink or meal may lead to feeling energetic in the short-term. Higher carbohydrate intake over a period of days is associated with better mood, but the reasons for this might be more complex than simple carbohydrates (e.g. better taste producing a better mood). A tendency for blood glucose levels to fall is associated with irritation and aggression; this can be stopped with a glucose containing drink. The theory that high carbohydrate meals make tryptophan levels rise seems to be relevant mostly under laboratory conditions, proteins in the meal are likely more important. To sum up, it seems that long-term eating habits and one's metabolic responses are more relevant for general mood than short term eating.
Harnessing the Power of the Continuum: Asynchrony, Emergence, and
David F. Delchamps
Nonlinear Science Today, 1995?
A fun article exploring the consequences of having continous time. It turns out that this enables Turing machines to compute uncomputable numbers. The proof is rather simple: imagine two Turing machines, one with clock frequency 1 and the other with frequency tau, which is irrational. If the first is programmed to output n ones and then halt when given the input n, and the other is programmed to output n zeros and then halt. A third machine simply concatenates the outputs as they arrive, creating a composite stream of interleaved ones and zeros. It turns out that this little machine can compute uncomputable numbers simply by selecting the right tau. Neat. The rest of the paper is a bit more speculative, and I don't buy the author's idea that brains become powerful by being parallel and exploiting continous times (then our thinking would be highly sensitive to delays, which occur naturally in aging). But it is definitely a fun way of extending the TM.
A quantum-dot neural network
E.C. Behrman, J. Niemel, J.E. Steck and S.R. Skinner In T. Toffoli, M. Biafore, and J. Leao (ed.) PhysComp96, New England Complex Systems Institute (1996) 22-24 Nov 1996
A mathematical implementation of an artificial neural network using the nonlinearities of interacting quantum systems. It employs the by now familiar "quantum dot molecules", where two electrons live in a five dot structure and can shift between two diagonal states, as influenced by neighboring molecules. The implementation appears to be able to both do traditional ANN calculations as well as quantum calculations.
Kristin Schleich, Donald M. Witt
Proceedings of the Lake Louise Winter Institute, Particle Physics and Cosmology, Feb. 20-26, 1994, (World Scientific, 1994) http://xxx.lanl.gov/abs/gr-qc/9903061
It is not just the Internet that suffers from censorship. Now it looks
like spacetime topology is censored too. Friedman, Schleich and Witt
have proven the topological censorship conjecture: that nontrivial
topologies (such as wormholes) have to be hidden behind horizons,
making them impossible to see (and use). More technically, if
spacetime is asymptotically flat, globally hyperbolic (i.e. physics
behaves in a predictable manner) and the averaged null energy
condition holds (energy densities can be negative locally as long as
the average energy is positive) then every causal curve
(i.e. trajectory of something) can be continously deformed to every
other curve. This paper gives an informal proof of this that is fairly easy to follow. Too bad for us would-be spacetime engineers, now we have to start looking for loopholes.
("I didn't say anything when they censored singularities, since I'm
nonsingular. I didn't say anything when they outlawed time travel with the Chronology Protection Conjecture, since I didn't want to kill my grandfather. Now they have censored wormholes, and I can't get anywhere" :-)
And a bit of science fiction:
The Wind from the Sun by Arthur C. Clarke
A collection of short stories he wrote in the 60's. Very much hard sf, with some stories of transhumanist interest. It is fascinating to notice how several of his ideas have become almost standard. "The Wind From the Sun" is in many ways the paradigmatic solar sail story about a race, carefully describing various sail geometries and problems. Maelstrom II is a nice "Man vs. physics" story, and according to the preface it seems that Clarke was first again with suggesting railgun launches from the moon with an article in the November 1950 issue of the Journal of the British Interplanetary Society. "Dial F for Frankenstein" is another classic paradigm-setter, with the now classic first line "At 0150 GMT on December 1, 1975, every telephone in the world started ringing". And the final story, "A Meeting with Medusa" has likely influenced practically every description of gas giant ecologies since then, but also has a quite transhumanist ending. Sometimes it is refreshing to go back to the classics just to see what got everything else started.
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