title: On the photovoltaic effect in local field potential recordings.
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.
authors.affiliation: Uppsala University , Unit of Developmental Genetics, Department of Neuroscience, Husargatan 3, 75237, Uppsala, Sweden.
authors.forename: Sanja
authors.initials: S
authors.lastname: Mikulovic
authors.affiliation: Uppsala University, Unit of Developmental Genetics, Department of Neuroscience, Husargatan 3, 75237, Uppsala, Sweden; Federal University of Rio Grande do Norte, Brain Institute, Avenida Nascimento de Castro, 2155, 59056-450, Natal-RN, Brazil.
authors.forename: Stefano
authors.initials: S
authors.lastname: Pupe
authors.affiliation: Federal University of Rio Grande do Norte , Brain Institute, Avenida Nascimento de Castro, 2155, 59056-450, Natal-RN, Brazil.
authors.forename: Helton Maia
authors.initials: HM
authors.lastname: Peixoto
authors.affiliation: Federal University of Rio Grande do Norte , Department of Biomedical Engineering, Avenida Senador Salgado Filho, 300, 59078-970, Natal-RN, Brazil.
authors.forename: George C
authors.initials: GC
authors.lastname: Do Nascimento
authors.affiliation: Uppsala University , Unit of Developmental Genetics, Department of Neuroscience, Husargatan 3, 75237, Uppsala, Sweden.
authors.forename: Klas
authors.initials: K
authors.lastname: Kullander
authors.affiliation: Federal University of Rio Grande do Norte , Brain Institute, Avenida Nascimento de Castro, 2155, 59056-450, Natal-RN, Brazil.
authors.forename: Adriano B L
authors.initials: AB
authors.lastname: Tort
authors.affiliation: Uppsala University, Unit of Developmental Genetics, Department of Neuroscience, Husargatan 3, 75237, Uppsala, Sweden; Federal University of Rio Grande do Norte, Brain Institute, Avenida Nascimento de Castro, 2155, 59056-450, Natal-RN, Brazil.
authors.forename: Richardson N
authors.initials: RN
authors.lastname: Leão
keywords: artifact; local field potential; optogenetics
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