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ref: -0 tags: optical coherence tomography neural recording squid voltage sensitive dyes review date: 12-23-2012 21:00 gmt revision:4 [3] [2] [1] [0] [head]

PMID-20844600 Detection of Neural Action Potentials Using Optical Coherence Tomography: Intensity and Phase Measurements with and without Dyes.

  • Optical methods of recording have been investigated since the 1940's:
    • During action potential (AP) propagation in neural tissue light scattering, absorption, birefringence, fluorescence, and volume changes have been reported (Cohen, 1973).
  • OCT is reflection-based, not transmission: illuminate and measure from the same side.
    • Here they use spectral domain OCT, where the mirror is not scanned; rather SD-OCT uses a spectrometer to record interference of back-scattered light from all depth points simultaneously (Fercher et al., 1995).
    • Use of a spectrometer allows imaging of an axial line within 10-50us, sufficient for imaging action potentials.
    • SD-OCT, due to some underlying mathematics which I can't quite grok atm, can resolve/annul common-mode phase noise for high temporal and Δphase\Delta phase measurement (high sensitivity).
      • This equates to "microsecond temporal resolution and sub-nanometer optical path length resolution".
  • OCT is generally (intially?) used for in-vivo imaging of retinas, in humans and other animals.
  • They present new data for depth-localization of neural activity in squid giant axons (SGA) stained with a voltage-sensitive near-infrared dye.
    • Note: averaged over 250 sweeps.
  • ΔPhase>>ΔIntensity\Delta Phase >> \Delta Intensity -- figure 4 in the paper.
  • Use of voltage-sensitive dyes improves the resolution of ΔI\Delta I , but not dramatically --
    • And Δphase\Delta phase is still a bit delayed.
    • Electrical recording is the control.
      • It will take significant technology development before optical methods exceed electrical methods...
  • Looks pretty preliminary. However, OCT can image 1-2mm deep in transparent tissue, which is exceptional.
  • Will have to read their explanation of OCT.
  • Used in a squid giant axon prep. 2010, wonder if anything new has been done (in vivo?).
  • Claim that progress is hampered by limited understanding of how these Δphase\Delta phase signals arise.