Abstract
Optogenetics allows light activation of genetically defined cell populations and the study of their link to specific brain functions. While it is a powerful method that has revolutionized neuroscience in the last decade, the shortcomings of directly stimulating electrodes and living tissue with light have been poorly characterized. Here, we assessed the photovoltaic effects in local field potential (LFP) recordings of the mouse hippocampus. We found that light leads to several artifacts that resemble genuine LFP features in animals with no opsin expression, such as stereotyped peaks at the power spectrum, phase shifts across different recording channels, coupling between low and high oscillation frequencies, and sharp signal deflections that are detected as spikes. Further, we tested how light stimulation affected hippocampal LFP recordings in mice expressing channelrhodopsin 2 in parvalbumin neurons (PV/ChR2 mice). Genuine oscillatory activity at the frequency of light stimulation could not be separated from light-induced artifacts. In addition, light stimulation in PV/ChR2 mice led to an overall decrease in LFP power. Thus, genuine LFP changes caused by the stimulation of specific cell populations may be intermingled with spurious changes caused by photovoltaic effects. Our data suggest that care should be taken in the interpretation of electrophysiology experiments involving light stimulation.
Highlights
Named the “method of the year 2010” according to Nature magazine,[1] optogenetics is revolutionizing neuroscience
In order to test whether the photovoltaic effect can produce LFPlike signals in typical optogenetic settings, we used silicon-substrate electrodes and an optical fiber to record local field potential (LFP) and deliver blue light in the intermediate/ventral hippocampal region
We have analyzed the interference of the photovoltaic effect on LFP recordings in commonly used silicon-substrate electrodes
Summary
Named the “method of the year 2010” according to Nature magazine,[1] optogenetics is revolutionizing neuroscience. First described by the French physicist Alexandre-Edmond Becquerel, the effect was noticed when metal electrodes in a slightly acidic solution were exposed to light, which resulted in the generation of electricity. The photovoltaic effect is produced by photonic excitation of electrons at the electrode valence band that absorbs the photon energy; these excited electrons leave their orbit, generating an electric potential.[8,9] Virtually every metallic conductor is prone to the photovoltaic effect as the conduction property of a given material implies weak binding of electrons at outer orbits
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