2009年10月31日

Evolution has no reverse

Whether evolution can go back to an ancestral structure just by reversing the selection pressure on function has been a long-standing issue but one hard to address based on just the history of forms.

Bridgham et al. have nowphysically reconstituted ancient versions of a regulatory protein (the glucocoricoid receptor) and dissected the structural constraints imposed on the evolution of their function (which hormone they bind) at atmic resolution.

They find that amino acids that were essential in an ancestral protein become newtral in a more recent from, where they are then subject to erosion by genetic drift.

This loss deprives natural selection of the necessary raw material with which to reverse the historical substitutions ― they are no longer 'adaptive' as they were in the other direction.

Evolutionarily spealing, there is no turning back.


### DataBace ###
nature Vol.461 837-1018 Issue no.7266 15 Octiber 2009
Letter p.515
Abstractions p.446
posted by 0≠素子 at 18:21| Comment(0) | evolution | このブログの読者になる | 更新情報をチェックする

2009年10月30日

The seat of literacy

Studing the changes that take place in the brain when we learn to read and write is very difficult as literacy is usually achieved during childhood, when many other developmental changes occur.

An opportunity to use brain imaging to study the process arose when a group of former guerrillas in Colombia, including some who had not been taught to read as children, were reintegrated
into Colombian society.

Comparing brain architecture of 'late literates' to their illiterate compatriots highlighted a number of brain areas potentially involved in the acquisition of literacy.

Interconnections between the left and right anglular gyri in the parietal lobe emerge as important for reading irrespective of age of reading acquisition and ability.


### DataBace ###
nature Vol.461 837-1018 Issue no.7266 15 Octiber 2009
Letter p.983 / An anatomical signature for literacy / M Carreiras te al.
Abstractions p.846 / First Author

posted by 0≠素子 at 19:56| Comment(1) | brain | このブログの読者になる | 更新情報をチェックする

2009年10月29日

The inside story on place cells

Neurons known as place cells encode spatial information that is needed to guide an animal's movement.

Nearly 40 years after these cells were discovered, neuroscience gets a look at their internal dynamics.


On page 941 (see page of this issue, Haevey et al.(Harvey,c.d.,Collman,F.,Do,bec,D.A.&Tank,D.W. Nature 461,941-946/2009) deecribe a novel combination of techniques that they have used to address unresolved questions about brain function.

The experiments involve mice navigating within a virtual-reality setting while intracellular electrophysiological recordingsare made of particular neurons ― pyramidal neurons ― in the hippocampus.

The ability to gather such data adds greatly to the information thatcan be glened from the accompanying extracellular recordings.


### DataBace ###
nature Vol.461 837-1018 Issue no.7266 15 Octiber 2009
Article p.941 / Intracellular dynamics of hippocampal place cells during virtual navigation / C D Harvey et al. (Princeton University)
News and Views p.889 / Neuro Science : The insade story on place cells / Douglas Niz


posted by 0≠素子 at 22:25| Comment(0) | neuron | このブログの読者になる | 更新情報をチェックする

2009年10月26日

Place cells know their place

As we move around, spatial information is encoded and processed by 'place' cells in the hippocampus.

Each of these neurons increases its firing rate when situated in its 'place', thus equating rate coding with location.

The firing patterns of hippocampal place cells have been studied extensively over the past 40 years and theoretical models have been proposed to explain the mechanisms responsible for encoding place and time in newral circuits.

Now the development of techniques allowing intracellular recording from place cells in awake, behaving mice navigating a virtual reality maze makes it possible to test these models.

Initial results point to the existence of two subthreshold signatures of place fields : an incrase in the amplitude of membrane potential oscillations at theta frequencies and a ramp - like depolarization of baseline membrane potential.


### DataBace ###
nature Vol.461 439-558 Issue no.7263 24 September 2009
Article p.941 / Intracellular dynamics of hippocampal place cells during virtual navigation / C D Harvey et al. (Princeton University)
News and Views p.889 / Neuro Science : The insaide story on place cells / Douglas Nitz


see
posted by 0≠素子 at 18:39| Comment(0) | brain | このブログの読者になる | 更新情報をチェックする

2009年10月24日

Prion disease transmission

Chonic wasting disease (CWD) is a highly contagious prion disease that causes neurodegeneration in several species in the deer family, including the elk and moose.

The precise mechanisms of natureal CWD transmission are unresolved.

IT is known that once an animal shows signs of the disease, its excretions can contain contagious prions.

Stanley Prusiner and colleagues show that mule deer in infected with CWD begin to excrete in fectious prions in faeces long before they develop visible signs of the disease.

This suggests a plausible, natural mechanism that could explain the high incidence and efficient horizontal transmission of CWD among deer - and may also be relevant for the similarly contagious scrapie in sheep.


### DataBace ###
nature Vol.461 439-558 Issue no.7263 24 September 2009
Letter p.529 / Asymptomatic deer excrete infectious prions / G. Tamguney et al. (University of California, San Francisco)

posted by 0≠素子 at 15:21| Comment(0) | medical science | このブログの読者になる | 更新情報をチェックする
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