X-Message-Number: 12573
From: Eugene Leitl <>
Date: Fri, 15 Oct 1999 11:10:00 -0700 (PDT)
Subject: New laser method reveals high-density information storage in the brain

I guess I don't have to explain anybody what this means in regards to
the impact of the freezing damage -- a yet another high watermark in
the trend that nature's gadgets are cleverer than we thought has been
reached.

It thus appears simply not prudent to adhere to the more optimistic
scenarios ("manipulation at molecular scale can repair any type of
damage"). Let's assume a worst-case, and see how much structural
damage we can eliminate by enhanced methods, (i.e. vitrification).

We obviously need a reliable, quantitative, observer-independant
metric to quantify the quality and quantity of the damage. This
relates to both measurement (optical, EM, cryo-AFM) and
interpretational (interpretation checklists, video DSP software)
domains.

Comments welcome. (I'll be travelling, so replies can take time).

http://www.mpg.de/news99/news44_99.htm

New laser method reveals high-density information storage
                     in the brain

Using a new method of infrared-guided laser stimulation,
researchers at the Max Planck Institute of Psychiatry in
Munich/Germany have discovered that information can be
stored in the brain with very high spatial density on the surface
of every single neuron (Science 1 October 1999). 

The new method was developed by Hans-Ulrich Dodt from the
Max Planck Institute of Psychiatry. In the past, he had developed
a method to visualize nerve cells in the depth of small pieces of
rat brain. To achieve this, Dodt used a microscope and infrared
light instead of normal light. In his new method, so-called
"infrared-guided laser stimulation", he coupled now a highly
precise UV-laser with his infrared microscope aiming with the
laser beam at neurons to be investigated. The method allows the
stimulation of selected target points on single neurons with a
spatial precision of 10 m m.

A solution was added to the brain slices which contained
neurotransmitter in a special chemical form, which becomes
only active if the so called ,caged neurotransmitter` is
illuminated by the UV-laser. Then, the neurotransmitter was set
free from its ,cage' at the point at which the laser aims. Thus, it
has become possible for scientists to do the same in the
laboratory what a synapse does in the brain, but now exactly at
the point and time when the scientist wants it. As this is
something that neuroscientists all over the world always wanted,
the method of "infrared-guided laser stimulation" will probably
be very quickly taken up by many other laboratories.

A research team (H.-U. Dodt, M. Eder, A. Frick, W.
Zieglg nsberger) at the Max Planck Institute for Psychiatry
applied the new method to investigate the so-called "long-term
depression" (LTD), a very important molecular mechanism in
the brain. Actually, mechanisms like long-term depression and
long-term potentiation (LTP) are regarded by many researchers
as the basis for memory formation in the brain. It has been
controversially debated how precise the underlying modifications
of the neuronal membrane can be and where these modifications
take place. The Max Planck researchers have discovered that
these modifications are spatially highly restricted. Thus,
information can probably be stored with very high density on the
surface of neurons. During the experiments, it became apparent
that a modification of the "receptor", the postsynaptic neuron, is
all what is needed to understand the mechanism of long-term
depression. Therefore, modifications of the amount of
neurotransmitter that is released during LTD can be neglected. 

As the UV-laser stimulation allowed the release of the
neurotransmitter glutamate from an inactive form of caged
glutamate in a very small region on the neuron, the researchers
could investigate how big the region on the neuron was that
experienced LTD. They found that this region was not bigger
than the resolution of their method, i.e. only a few Micrometer.
Thus, even single synapses may undergo long-term depression
and each single synapse could be used to store information
separately from its neighbour. One could compare this possibility
for information storage in the brain with the "high densitiy
information storage" on a CD-ROM.

Figure 1: 
Pyramidal neurons in the network of the neocortex visualized
with infrared videomicroscopy in rat brain slices.

Figure 2: 
Experimental set-up used for infrared-guided laser stimulation.
Neurons in the brain slice were visualized by illumination with
infrared light and the gradient contrast system. At the same
time, light pulses of an UV-laser were fed via a quartz fibre into
the microscope and directed by a dichroic mirror onto the
recorded neuron. Both the slice chamber and the microscope
could be positioned in x-y remote controls. The laser spot of an
optical diameter of 1 m m formed by the objective (60X, 0.9 N.A.,
Olympus) in the specimen plane was made visible before the
experiment by a fluorescent paper, and its position marked on
the TV monitor. By positioning of the neuron to be stimulated on
this point, the laser stimulation could be precisely guided by
visual control.



                                   Published: 30-09-99 
                              Contact: Hans-Ulrich Dodt
                       Max-Planck-Institute of Psychiatry, 
                                      Munich/Germany
                              Phone: (+49 89) 30622-344
                                      Fax: (+49 89) 30622-200

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