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Neuroimage. 2013 Feb 1;66:634-41. doi: 10.1016/j.neuroimage.2012.10.074. Epub 2012 Nov 2.

fMRI response to blue light delivery in the naïve brain: implications for combined optogenetic fMRI studies.

Author information

  • 1UCL 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.
  • 2UCL 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.
  • 3Royal Institution of Great Britain, Davy-Faraday Research Laboratory, London, UK.
  • 4Neuroscience, Physiology and Pharmacology, University College London, London, UK.
  • 5School of Physiology and Pharmacology, University of Bristol, Bristol, UK.
  • 6UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK.

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.

KEYWORDS:

Artefact; Heating; MRI; Opto-fMRI; Optogenetics; fMRI

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