Tuesday, September 9, 2008

LHC and the God Particle

First of all, I am way, way too excited for Wednesday.

Murray Gell-Mann simplified the zoo of fundamental physical particles in the 1960's by identifying their similarities in their symmetries. All 80 (or something) types were made up of three quarks. In the late 60's, the first electron micrographs of protons were taken, finding within this fundamental particle three smaller particles of the correct charges, but of indiscernible structure. These quarks, together with the electron and electron neutrino are capable of explaining everything in the actual world. Among the things that remain unexplained is why there are three families of each of the aforementioned, which are identical in every respect except that they are of three different masses. How is it possible that there are, in perceivable existence, three versions of the exact same fundamental particle which perform the exact same function and have what appears to be the exact same structure?

There is another particle, called a Higgs boson, which - should it actually exist - answers the profound question of why and how things acquire different masses, why so many distinct fundamental particles can arise from the same three quarks, why unique particle interactions occur in particular fashions, and exactly which roles those forces play in our universe.

Particles gain different masses because of the different ways in which they interact with Higgs bosons. Essentially (and I'm not going to try to tackle the actual equations because my mind is feabile and my brain is exhausted), Higgs particles are dark matter. They fill every "empty" space in the universe, and as fundamental particles stream through the universe, those that are said to acquire mass are bombarded with Higgs bosons which slow down their streamline. Those particles which do not acquire mass (photons, etc.) are not impeded by Higgs particles... hence, nothing travels faster than the speed of light :)

The Large Hadron Collider at CERN has been designed (and under construction and legal debate since 2003) to see if the Higgs boson can be revealed. The problem with the Higgs boson theory right now is that it is just mathematical theory - there is no physical observation. The idea behind the LHC is that, as it is a particle accelerator, the collision of protons accelerated within it can result in the creation of a new particle. The energy created by the collision is proportional to a mass (this is the real meaning of E=mc^2), and so a new particle with a new mass can result.

This is why tomorrow is so fucking sweet. Tomorrow... Sept. 10, 2008... and more importantly, Wednesday... the LHC will be "turned on," and the first proton beam will be circulated through the tunnel. The Tevatron particle collider in the Fermi Lab outside Chicago is almost as powerful as CERN's LHC, and may have already shown the existence of the Higgs boson, but have not produced any data, as such. The idea of the LHC is to recreate the conditions up to milli-seconds following the Big Bang, and hopefully make strong suggestions about the nature of this minor event in history.

The identification of the Higgs boson would mean remarkable things for the entire world of physics, beginning with the completion of the Standard Model of particle physics. Specifically, the Higgs boson would give a distinct variable to the differences between massive and massless particles, thus making possible concrete suggestions (as opposed to theoretical) about the nature of the relationship between the four fundamental forces (electromagnetism, gravitation, weak and strong nuclear forces).

Ergo... more redefinition and tweaked theory of the Big Bang.


Saturday, September 6, 2008

REM and memory consolidation

consolidation of memories - being the enhancement and stabilization following encoding of information - primarily occurs during sleep. there are, as to be expected, several propositions as to the manner in which this takes place.

the medial temporal lobe, including the hippocampal system, is said to mediate consolidation through enhancing innervation to the neocortex. it is proposed that this occurs in several possible mechanisms:

1) the MTL system consolidates by signaling the neocortex to form a new representation of information, and the neocortex subsequently imprints and stores

2) the MTL is the rehearsal mechanism, strengthening connections with the particular cortical regions so they are all activated when the experience responsible for the information input repeats in the future

3) the MTL encodes AND imprints memories into the neocortex. this final option suggests that once enhanced, the neocortex is the final repository for memories. long-term memory is then distributed by coactivation through the higher neocortices specialized for analysis, each contributing differently to the storage of the complete memory. in this way, the neocortex is primed to reconstruct the representation of the information from partial cues.

regardless of which of these mechanisms is more correct than the other, their common function depends on adequate sleep cycles. it has been shown that not only does consolidation occur primarily during slow-wave and REM sleep (Kandel 2001, Sei et al 2000), but also that MTL activity during the information encoding process decreases dramatically in sleep deprived subjects (Drummond et al 2000). both of these observations correlate with decreased cortical metabolism and reproducible memory deficit.

disruption of encoding and deficit of retention in sleep-deprived subjects map onto particular physiological correlates that pronounce REM sleep as crucial for the memory consolidation process. REM deprivation reduces excitability of hippocampal neurons responsible for imprinting information into the neocortex (Kandel). this, as you might imagine, directly impairs long-term potentiation (LTP), or decays any LTP that does occur [ aka, early-LTP is vulnerable to decay within 90 min if not pushed into late-LTP by excited hippocampal neurons which facilitate the genetic transcription of proteins which are biochemically responsible for the actual "long term"]. in addition to LTP, acetylcholine (ACh) accompanying slow-wave sleep just prior to REM mediates consolidation (Power 2004, see neato pic).

the other important gesture sustained by REM sleep is the production of several nerve growth factors, primarily NGF and BDNF. these are both key regulators of LTP (again referring to the strengthening of neural circuit connections in learning and memory formation). this means that their reduction in REM sleep-deprived subjects probably causes the impairment in memory consolidation - supported by the most drastic deficits occurring in the hippocampus.

apparently, episodic memory is most profoundly affected by REM sleep-deprivation... but we don't know why (Rauchs et al 2004). although it wouldn't surprise me in the least if it had something to do with consolidation involving the prefrontal cortex (which has been suggested by almost everyone in the field to be the primary region of activation and most distinguishable candidate during episodic memory retrieval, and also during MTL mediated consolidation (see entry on "episodic memory and autonoetic awareness")). both the hippocampus and pfc are main players in episodic memory encoding and retrieval (id est, emotional memory depicting information in the context which it was learned). the other half of declarative memory, semantic, seems to involve a much different array of hippocampal efferent circuits. and although i don't actually know what the profiles of ACh, NGF or BDNF are in those circuits... i would imagine that they're also different from the activity seen in the circuits associated with episodic consolidation.

ergo, REM sleep: fighting amnesia since the evolution of the higher limbic system.


do dreams arise from the stochastic hippocampal inputs to the neocortex?

did dreams evolve from the prolonged quiescent state in reptiles to promote calcium-dependent memory consolidation?