They are Larry Cohen, Chun
X. Bleau, Dejan Zecevic, Brad Baker, Stratos
Kosmidis and Riota Homma.
One
reason the brain is difficult to study is that many individual
neurons or brain areas are active at once; conventional
techniques allow one to monitor only one or a few neurons or
locations at a time. We have worked on several variations of an
optical method for measuring brain activity; utilizing both voltage-sensitive dyes and calcium-sensitive
dyes and either a 464 element photodiode array (see photograph of array) or a 80x80 CCD
camera. Both systems are fast; frame rates >1.6kHz.
In the First variation (Population Signals, Larry Cohen), each pixel in the recording receives light from a large number of neurons and processes (e.g. from an area of brain 10µm x 10µm to 200µm x 200µm) and thus each signal represents the average of a population of neurons. There are several interesting aspects of vertebrate brain function where populations are involved. One example is the organization of visual cortex into modules such as ocular dominance columns. Another is the synchrony and oscillations that accompany sensory processing. A third is maps of the input to glomeruli in the olfactory bulb where 10,000 receptor neurons with identical olfactory receptor protein converge onto a single glomerulus. For studying phenomena of this type population recordings should be useful.
In the Second variation (Inside Dyes, Dejan Zecevic), each pixel in the recording receives light from a small portion of a neurons which has been stained by microinjection of the dye into the cell body. 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.
In the Third variation (Action Potential Signals), we use the dyes to follow the spike activity of individual neurons, and in favorable preparations about 500 individual neurons can be monitored simultaneously. In ganglia from sea slugs (opisthobranch molluscs, Aplysia), this number is a substantial fraction of the total number of neurons present. We hope that monitoring many neurons simultaneously will improve our understanding about how nervous systems are organized to generate behaviors.
The figure illustrates the voltage-sensitive dye signal (dots) and the action potential (smooth line) measured simultaneously from a squid giant axon. The two signals follow each other precisely providing one kind of evidence that this dye signal is potential dependent.
Ross, W.N., B.M. Salzberg, L.B. Cohen, A. Grinvald, H.V. Davila, A.S. Waggoner, and C.H. Wang (1977). Changes in absorption, fluorescence, dichroism, and birefringence in stained giant axons : optical measurement of membrane potential. J Membr Biol, 33, 141-183.
Ours
is a small laboratory in the Department of Physiology. It
consists of two PIs each with one to three other scientists. One of the
reasons for having a small
laboratory is that the PIs still enjoy doing experiments and a
large laboratory makes that impossible. In addition, there are
only two experimental set-ups. Thus, the planning, the
experiments, and the analysis have always been done in a very
collaborative fashion with everyone sharing their opinions and
efforts.
You may
have noticed that all of the individuals are smiling. This must
mean that the experiments are easy.
(Left to Right)
Srdjan Antic: Department of Neurobiology, Yale University
School
of Medicine
Tsau Yang
Chris Hickie: University of Connecticut Medical
School.
Avrum Cohen's Homepage.
Avrum was a programmer at the lab off and on until his employment
at Universal Imaging Corporation
in December of 1995.
Fang Jing
Lam Ying-Wan: Department of
Neurobiology, SUNY Stony Brook.
Michal Zochowski Department
of Physics, University of Michigan.
Matt Wachowiak Department
of Biology, Boston University.
Dejan Vucinic Department of
Physiology, Northwestern University.
Maja Djurisic Department of
Neurobiology, Harvard Medical School.
