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 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.
- -- figure 4 in the paper.
- Use of voltage-sensitive dyes improves the resolution of , but not dramatically --
- And 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 signals arise.
|