Led by Professor Lawrence E. Cohen Ph.D. of Yale University's
Department of Cellular and Molecular Physiology, the small
lab in room BESS at the Yale School of Medicine has been conducting
research on neuronal activity in brain cells to develop methods
for imaging brain activity, and then uses these methods to
study the brain. The university has been developing the method
for imaging brain activity for 42 years, but it was not until
several years ago that the lab opted to move to a higher level
of vibration isolation technology to support its microscopy
imaging which it conducts at the micron level.
It is not unusual for universities, and industry for that
matter, to have to deal with problems in site vibration which
compromise to a greater or lesser degree the imaging quality
and data sets which they acquire through microscopy. Although
it is certainly the desire of every lab to rid the unwanted
vibration, conventional systems such as air tables which many
universities and industry labs still use, have not been successful
in providing an adequate level of vibration isolation for
ultra-sensitive equipment measuring at the Angstrom and micron
levels.
Such was the case with Dr. Cohen's lab at Yale, where air
tables had been the mainstay for the lab's vibration isolation
for many, many years. But now, for adequate isolation to conduct
its neuronal research at the micron level, the air tables
were not able to provide the vibration isolation needed for
the lab's research.
Measuring Brain Activity"
One reason the brain is difficult to study is that many individual
neurons or brain areas are active at once, and conventional
electrode techniques allow monitoring of only one or a few
neurons or locations at a time," said Dr. Cohen. "We
have worked on several variations of an optical method for
measuring brain activity, utilizing both voltage-sensitive
and calcium-sensitive dye methods to study neuron activity,
and in favorable preparations the spike activity of about
500 individual neurons or thousands of brain regions can be
monitored simultaneously. These methods have good temporal
(msec) and spatial (10s of microns) resolution.
""Monitoring many neurons or regions simultaneously
can improve our understanding about how nervous systems are
organized," continued Cohen. "Recently, we have
used these methods to study the processing of olfactory information
in the turtle and mouse. We have obtained maps of the input
to the olfactory bulb which define the responsiveness of individual
olfactory receptor proteins. In the future, we hope to obtain
maps of the output of the bulb. A comparison of the two maps
can provide a powerful description of the role of the olfactory
bulb in processing olfactory signals."
"Basically, depending on the dye, we are viewing the
voltage across the neuron membrane or the calcium concentration
inside the neuron," Cohen adds. "When the action
potential travels along the nerve and comes to the nerve terminal
it releases a chemical that acts on the adjacent nerve cell.
In order to release that chemical it opens a calcium channel.
Calcium comes into the nerve terminal, and that calcium causes
a vesicle - which is filled with chemical substances, to fuse
with the membrane, and the transmitter substance is released."
"The voltage is the signal that the cell uses to carry
information from one end to the next," explains Cohen.
"For example, the cells in your spinal cord have to get
information from your toe, and also send information to your
toe. That signal is a propagated electrical wave of membrane
potential, and dyeing that membrane can provide an optical
signal that is used to measure that propagated wave."
Precision Equipment
The lab uses a high-speed camera to view these changes. It
has a speed of 2,000 frames-per-second with very high quantum
efficiency, which is the quantity of photons that get converted
into electrons. The camera has a quantum efficiency of about
.9, which converts almost all the photons into electrons.
(In contrast, photographic film has a quantum efficiency of
<.01, converting less than 1 percent of photons into darkened
silver grains.)
In the lab's optical monitoring of brain activity, each pixel
in the recording receives light from a small portion of neurons
which have been stained by microinjection of the dye into
the brain. After waiting for the dye to spread into the processes,
the dye can be used to monitor changes in membrane potential
in dendrites and axons.
When a low magnification objective is used to form an image
of a vertebrate preparation on the lab's 464 element photodiode
array or 80 x 80 pixel CCD camera, each pixel receives light
from hundreds or thousands of neurons. The signals are the
population average of the membrane potential or calcium concentration
changes in those neurons. These population signals monitor
coherent activity - those events that involve simultaneous
changes in activity of a substantial fraction of the neurons
in the imaged region.It is also using a variety of microscopes
to conduct this research including a laser scanning 2-photon
microscope, and an optical microscope. At this time, only
the optical microscope is set on the Negative-Stiffness vibration
isolation system, built by Minus K Technology (http://www.minusk.com).
Vibration Noise
"Measuring in the dimension of microns still requires
vibration isolation because it is so small," said Cohen.
"Any small movement in the lab environment makes a big
effect. If you are viewing at ten microns, and it vibrates
by ten microns then you are in big trouble."
"We were using air tables before, but the Negative-Stiffness
isolator is much better," Cohn continued. "It reduces
the vibration by a larger faction because it reduces the vibration
in the X/Y plane just as well as in the Z plane, where the
air table does not do well at all on the X/Y plane."
"For years we have worked hard to get rid of vibration
noise, with only partial success," Cohen added. "Our
lab is located one floor above the basement. Having been in
the business a long time I know if we were in the basement
it would be better. I have had my lab in places that are quieter.
Since we put in the Negative-Stiffness system several years
ago, we have not had to think about vibration noise at all.
Before, there was always vibration noise, and would spend
5 to 10 percent of my time worrying about vibrations."
Negative-Stiffness Vibration Isolation
Negative-Stiffness isolators employ a unique - and completely
mechanical - concept in low-frequency vibration isolation.
Vertical-motion isolation is provided by a stiff spring that
supports a weight load, combined with a Negative-Stiffness
mechanism. The net vertical stiffness is made very low without
affecting the static load-supporting capability of the spring.
Beam-columns connected in series with the vertical-motion
isolator provide horizontal-motion isolation. The horizontal
stiffness of the beam-columns is reduced by the "beam-column"
effect. (A beam-column behaves as a spring combined with a
Negative-Stiffness mechanism.) The result is a compact passive
isolator capable of very low vertical and horizontal natural
frequencies and very high internal structural frequencies.
The isolators (adjusted to 1/2 Hz) achieve 93% isolation efficiency
at 2 Hz; 99% at 5 Hz; and 99.7% at 10 Hz.
Vibration Isolation in Bio-Research
Yale University has put into place a vibration isolation solution
which correctly matches the precision level of the research
the lab is undertaking. It is critical that researchers apply
the correct vibration isolation solution to their sites. Putting
up with lab vibration noise problems for any amount of time,
let alone for a period of years, can only be costly in terms
of lost production, and will certainly inhibit the progress
of the research.
Bio-research is expanding at a huge rate into scores of different
disciplines and literally hundreds of diverse applications.
This will inevitably mean a sizable increase in the number
of non-optimum, high-vibration-prone labs sites that will
be in desperate need of truly functional vibration isolation.
Hopefully, with the help of Negative-Stiffness vibration isolation,
your site will not be one of them.
Dr. Lawrence B. Cohen is Professor of Cellular & Molecular
Physiology at Yale University, School of Medicine, Department
of Cellular & Molecular Physiology. He holds a B.A. from
the University of Chicago, and received his Ph.D. from Columbia
University in 1965. He can be reached at Yale University,
School of Medicine BK58 SHM, 333 Cedar Street, New Haven,
CT 06520-8026; email lawrence.cohen@yale.edu; http://info.med.yale.edu.
Dr. David L. Platus is the inventor of negative-stiffness
mechanism vibration isolation systems, and president and founder
of Minus K Technology, Inc. (http://www.minusk.com). He earned
a B.S. and a Ph.D. in Engineering from UCLA, and a diploma
from the Oak Ridge School of (Nuclear) Reactor Technology.
Prior to founding Minus K Technology he worked in the nuclear,
aerospace and defense industries conducting and directing
analysis and design projects in structural-mechanical systems.
He became an independent consultant in 1988. Dr. Platus holds
over 20 patents related to shock and vibration isolation.
Minus K Technology, Inc. was founded in 1993 to develop, manufacture
and market state-of-the-art vibration isolation products based
on the company's patented negative-stiffness-mechanism technology.
Minus K products, sold under the trade name Nano-K, are used
in a broad spectrum of applications including nanotechnology,
biological sciences, semiconductors, materials research, zero-g
simulation of spacecraft, and high-end audio. The company
is an OEM supplier to leading manufactures of scanning probe
microscopes, micro-hardness testers and other vibration-sensitive
instruments and equipment. Minus K customers include private
companies and more than 150 leading universities and government
laboratories in 25 countries.
For more information, contact Steve Varma, Minus K Technology,
Inc.; 460 South Hindry Ave., Unit C; Inglewood
