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

Simon Schultz s.schultz at imperial.ac.uk
Tue Feb 5 12:16:20 CET 2013

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

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.


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