title: fMRI response to blue light delivery in the naïve brain: implications for combined optogenetic fMRI studies.
abstract: The combination of optogenetics and functional magnetic resonance imaging (fMRI) is referred to as opto-fMRI. Optogenetics utilises genetic engineering to introduce light sensitive actuator proteins into cells. Functional MRI (fMRI) is a specialist form of magnetic resonance imaging concerned with imaging changes in blood flow and oxygenation, linked to regional variation in metabolic activity, in the brain. This study describes a methodological concern regarding the effects of light delivery into the brain for the purposes of opto-fMRI. We show that blue light delivery to the naïve rat brain causes profound fMRI responses, despite the absence of optogenetic activation. We demonstrate that these fMRI responses are dependent upon laser power and show that the laser causes significant heating. We identify how heating impacts upon the MR signal causing NMR frequency shifts, and T1 and T2* changes. This study brings attention to a possible confounder which must be taken into account when opto-fMRI experiments are designed.
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK; Neuroscience, Physiology and Pharmacology, University College London, London, UK.
authors.forename: Isabel N
authors.initials: IN
authors.lastname: Christie
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK. Electronic address: jack.wells@ucl.ac.uk.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Wells
authors.affiliation: Royal Institution of Great Britain, Davy-Faraday Research Laboratory, London, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Southern
authors.affiliation: Neuroscience, Physiology and Pharmacology, University College London, London, UK.
authors.forename: Nephtali
authors.initials: N
authors.lastname: Marina
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, UK.
authors.forename: Sergey
authors.initials: S
authors.lastname: Kasparov
authors.affiliation: Neuroscience, Physiology and Pharmacology, University College London, London, UK.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Gourine
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK.
authors.forename: Mark F
authors.initials: MF
authors.lastname: Lythgoe
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D062308:Optogenetics / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: Artefact; Heating; MRI; Opto-fMRI; Optogenetics; fMRI