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ref: -0 tags: histology optical coherence tomography vasculature avoidance date: 01-29-2013 06:46 gmt revision:0 [head]

PMID-9766311 Optical coherence tomography for neurosurgical imaging of human intracortical melanoma.

  • Relevant for our interests: Subsurface cerebral vascular structures could be identified and were therefore avoided.
  • more broadly, could identify subsurface metastatic melanoma due to reflectance changes. nice.

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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.

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ref: -0 tags: optical coherence tomography neural recording aplysia date: 12-23-2012 09:12 gmt revision:2 [1] [0] [head]

PMID-19654752 Detecting intrinsic scattering changes correlated to neuron action potentials using optical coherence imaging.

  • Aplysia, intrinsic imaging of scattering change following electrical stimulation.
    • Why did it take so long for them to get this paper out.. ?
  • Nicolelis first cited author.
  • Quality of recording not necessarily high.
  • quote: "Typical transverse resolutions in OCT (10-20um) are likely insufficient to identify smaller mamallian neurons that are often studied in neuroscience."
    • Solution: optical coherence microscopy (OCM), where a higher NA lens focuses the light to a smaller spot.
    • Expense: shorter depth-of-field.
  • Why does this work? "One mechanism of these optical signals is believed to be a realignment of charged membrane proteins in response to voltage change [6].
  • A delay of roughly 70ms was observed between the change in membrane voltage and the change in scattering intensity.
    • That's slow! Might be due to conduction velocity in Aplysia.
  • SNR of scattering measurement not too high -- the neurons are alive, afterall, and their normal biological processes cause scattering changes.
    • Killing the neurons with KCl dramatically decreased the variance of scattering, consistent with this hpothesis.
  • Birefringence: "Changes in the birefringence of nerves due to electrical activity have been shown to be an order of magnitude larger than scattering intensity changes" PMID-5649693

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ref: Brown-2001.12 tags: EMG ECoG motor control human coherence dopamine oscillations date: 01-19-2012 21:41 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-11765129[0] Cortical network resonance and motor activity in humans.

  • good review.
  • No coherence between ECoG and eMG below 12 Hz; frequency coherence around 18 Hz.
    • This seen only in high-resolution ECoG; lower resolution signals blurs the sharp peak.
  • Striking narrowband frequency of coherence.
  • ECoG - ECoG coherence not at same frequency as EMG-ECoG.
  • Marked task-dependence of these coherences, e.g. for wrist extension and flexion they observed similar EMG/ECoG coherences; for different tasks using the same muscles, different patterns of coherence.
  • Pyramidal cell discharge tends to be phase-locked to oscillations in the local field potential (Murthy and Fetz 1996)
    • All synchronization must ultimately be through spikes, as LFPs are not transmitted down the spinal cord.
  • Broadband coherence is pathological // they note it occurred during cortical myclonus (box 2)
  • Superficial chattering pyramidal cells (!!) firing bursts of frequency at 20 to 80 Hz, interconnected to produce spike doublets (Jefferys 1996).
  • Dopamine restores coherence between EMG and ECoG in a PD patient.

____References____

[0] Brown P, Marsden JF, Cortical network resonance and motor activity in humans.Neuroscientist 7:6, 518-27 (2001 Dec)