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NPB163-L2

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📗 -> 04/02/25: NPB163-L2

[Lecture Slide Link]

🎤 Vocab

❗ Unit and Larger Context

Small summary

✒️ -> Scratch Notes

Practice:

How to:

  • Extracellular recording?
    • Electrode
  • Intracellular recording?
    • Insert a —
    • Patch clamp, seal the membrane
    • What do we measure?
      • Membrane potential
      • EPSP / IPSP
  • ECoG / iEEG
    • Electrode grid placed on the surface of the brain
    • Measures population activity
  • Optical Imaging
    • There is intrinsic / voltage sensitive dye / calcium sensitive dye
      • Intrinsic - Measure reflectance of the light, measure oxygen consumption of area
      • Indirect measure of activity

Today’s Class - Non-invasive

EEG / MEG / fMRI

EEG

Noninvasive measure popular in cognitive neuroscience
EEG signal is an aggregate signal that has been heavily filtered (volume conduction, skull); localizing the source of a signal component is difficult; temporal resolution is good

How?

  • Positive charge gets into dendrites, leaves negative charge outside
    • Creates a dipole:
      • Positive on cell body
      • Negative on cell dendritic synaptic terminals

EEG is primarily used to measure either evoked potentials or oscillatory activity at various frequencies

MEG

  • On top of measuring electric field, we can measure the magnetic field.
  • With MEG, we measure the magnetic field around the head generated by eletric activity in the brain
  • Less popular than EEG due to its equipment (expensive, bulky)
  • Better spatial resolution than EEG, magnetic field less distorted by skull and scal than the electric field

Apparently there's a lot of online resources about MEG data?

fMRI

  • fMRI is probably the most popular technique for noninvasively measuring neural actvity in - cognitive neuroscience.
  • It is an indirect measurement of neural activity, providing a Blood Oxygenated Level Dependency - (BOLD) signal
  • A strong static magnetic field (B0) is used to align spins (of, e.g., protons in water or fat in body tissue).
  • A radiofrequency (RF) magnetic field (B1) causes spins to flip (transient loss of alignment with B0 field) and to phase-synchronize.
  • Signals resulting from the realignment of the spins with the B0 field and from phase desynchronization are measured.
  • Gradient fields are used to make the measurement spatially selective

T1 and T2 components:

  • T1 spin-lattice relaxation time?
    • Used for anatomic imaging
  • T2 spin-spin relaxation time?
    • More measuring how synchronized different protons are
  • important component for fMRI; measurement of local field inhomogeneities resulting from the paramagnetic properties of deoxyhemoglobin

Time delay:

  • Intrinsic imaging will analyze the initial dip, while fMRI will measure the hemodynamic peak
  • Also be careful of what we are actually measuring:
    • BOLD correlates with energy demanding activity. This is not necessarily spiking activity.
    • Strongly influenced by dendritic activity

Check the lecture slides 40-41 for technique tables. Very helpful

Interpreting Neural Activity

We cannot assume causation, merely correlation a lot of the time.
Easy example:

  • Knee reflex:
    • You’ll see activation in both somatosensory cortex, and the reflex.
    • However, they are not linked. It is the sensory nerve that invigorates both. This causes linked/correlated activity, but no causal connection.

Establishing a causal relationship requires manipulation of neural activity.

  • Traditionally, this was done through lesion studies.
    • Phineas Gage e.x.
    • They used his lesion to link the prefrontal cortex to self control.
  • However, waiting for specific patients is infeasable.

Experimental Lesions:

  • Advantage of being able to define location of lesion
  • Options to do it surgically or chemically
  • However, irreversible
    Reversible Inactivation:
  • Allow study of before / during / and after inactivation.
  • Possible chemically
  • Possible with an implanted cooling device (cooling chip / cryoloop)

More Stim

Microstimulation

REVIEW

Optogenetic Stimulation

Introduce molecules that can be light-activated into the cell membrane in order to depolarize or hyerpolarize the neuron

  • Channels for both:
    • Depolarization (light gated leak channel)
      • Channelrhodopsins
    • Hyperpolarization (active pumps)
      • Halorhodopsins
      • Archaerhodopsins
        Typically done by creating transgenic animals or viral-based gene delivery

The advantage of optogenetics is that specific cells can be genetically targeted such that only a particular type of neurons is affected by the stimulation
The disadvantage is with viral-based delivery, the viruses used as vectors have their own cell specificity

Questions?

  • Review optical imaging
  • What is T3 measuring?
    1. Hell whats is T2 measuring

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