[Comp-neuro] Computational optogenetics paper now available as open access

Dear Colleague,

Please note that the following paper, recently published in JCN, is now
available via Open Access:

The spatial pattern of light determines the kinetics and modulates
backpropagation of optogenetic action potentials
Nir Grossman, Vasiliki Simiaki, Claire Martinet, Christofer Toumazou,
Simon R. Schultz, Konstantin Nikolic

Abstract
Optogenetics offers an unprecedented ability to spatially target
neuronal stimulations. This study investigated via simulation, for the
first time, how the spatial pattern of excitation affects the response
of channelrhodopsin-2 (ChR2) expressing neurons. First we described a
methodology for modeling ChR2 in the NEURON simulation platform. Then,
we compared four most commonly considered illumination strategies
(somatic, dendritic, axonal and whole cell) in a paradigmatic model of a
cortical layer V pyramidal cell. We show that the spatial pattern of
illumination has an important impact on the efficiency of stimulation
and the kinetics of the spiking output. Whole cell illumination
synchronizes the depolarization of the dendritic tree and the soma and
evokes spiking characteristics with a distinct pattern including an
increased bursting rate and enhanced back propagation of action
potentials (bAPs). This type of illumination is the most efficient as a
given irradiance threshold was achievable with only 6 % of ChR2 density
needed in the case of somatic illumination. Targeting only the axon
initial segment requires a high ChR2 density to achieve a given
threshold irradiance and a prolonged illumination does not yield
sustained spiking. We also show that patterned illumination can be used
to modulate the bAPs and hence spatially modulate the direction and
amplitude of spike time dependent plasticity protocols. We further found
the irradiance threshold to increase in proportion to the demyelination
level of an axon, suggesting that measurements of the irradiance
threshold (for example relative to the soma) could be used to remotely
probe a loss of neural myelin sheath, which is a hallmark of several
neurodegenerative diseases.

http://link.springer.com/article/10.1007%2Fs10827-012-0431-7
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