Summary
Summary Functional Imaging (MED-BMS25)
- Course
- Institution
All lectures and slides
[Show more]
Seller
Follow
kimvandenbroek83
Reviews received
Content preview
Electrophysiologyelectrophysiology: using the electrical activity generated by the nervous system to study
neural computation, cognition, and behavior
→ cognition, emotions, etc. range from 1 to 100 Hz
How to measure neuroelectric signals
- intracellular recording: measuring from inside the neuron
- juxtacellular recording: measuring next to one specific cell in the membrane of the
brain
- extracellular recording: measuring spikes in the brain (one electrode)
- LFP/iEEG: measuring the sum of potentials in the brain (more electrodes)
- ECoG: measuring electric current on the dura (like EEG but the electrode is placed
under the skull (not in the brain))
- M/EEG: measurement outside of the head (non-invasive) → every magnetic field you
have has a perpendicular electric field
- MUA: measure collection of spikes (a little bit like LFP)
→ the further you get from the neuron, the weaker the potential that you measure with your
electrode
Advantages of electrophysiology
- cognition = fast → ephys captures this in the time-frame in which events occur (fMRI
cannot do this due to low temporal resolution) → direct measure of electrical brain
activity
- provides complex data → analyses of local regions and networks (fMRI is only one-
dimensional (up or down signal))
- link across scales/methods and species
→ species with different sizes of brains all have similar neural oscillations at almost
the same speeds (oscillations are constant across species)
Disadvantages of electrophysiology
- limited to large-scale potentials → field-cancellation might occur
- uncertainties in anatomical localization (low spatial resolution)
- data analysis is complicated, time-consuming, and annoying
- high temporal resolution → if you don’t exactly know what you are looking for you
might have a hard time finding it
How to analyze spiking data
problem: one electrode, many neurons
- use a low-pass spatial filter (LFP filter) to get local field potential
, - use spike filter → spikes contain information from many different neurons → use spike
sorting (assign each spike to a different neuron)
Traditional solution (to the aforementioned problem):
● intra/juxtacellular ephys → only measure one neuron (takes a long time to collect
data, and is ethically not doable)
Modern solution:
● spike-sorting (spike extraction → waveforms alignment → principal components
analysis → clustering (algorithm to separate spikes) → sorted waveforms)
- there are a lot of algorithms that solve this problem (hard to solve)
- spike-sorting leads to spikes going missing
, ● population → one neuron does not do exactly one thing, so we look at groups of
neurons that fire together
How to analyze LFP/MEEG data
- task-related vs. continuous
ERPs: event-related potentials → task-related analyses → take the average of all trials
- time-domain
- spectral domain
- time-frequency domain
Fourier transform: take a signal and take a sine wave as template and look at how similar
the signal is to the sine wave (phase-dependent)
power time series: amplitude time series tot de macht 2
Time-frequency plot: red is more energy, blue is less energy
- LFP is a complex and mysterious signal (lots more research to be done)
- spike sorting is also complex and mysterious
EEG data acquisition and analysis
Recording methodologies of EEG
● 10-20 system → 10 and 20% distance, odd numbers left side, even numbers right
side, A1 and A2 are reference electrodes that are placed behind ear since there
should be no electric current
, ● 15 channel SOMNO screen → home recording (for sleep eg)
● 32/64 channel Easycap/acticap + brainamp → lab recordings → there are passive and
active electrodes (active are less comfortable but better)
● 128 channel Easycap/brainamp → lab recordings
● 256 channel → too many electrodes is not always better
- caps come in all sizes (also for babies and for different head shapes)
Combinations of EEG
- EEG and fMRI → leads to a lot of artifacts and thus worse signal → measure EEG
when MRI pulse is off for better signal
- EEG and NIRS → works well in easily accessible regions from the skull
NIRS: near-infrared spectrometer → measures oxygenation of blood → better spatial
resolution than EEG
Wearable EEG caps
● lead to a lot of motion artifacts (most difficult to filter out)
- Zmax: EEG headband → limited to frontal region but you don’t have a problem with
hair
- in-ear EEG: only temporal areas, dry contact electrode (no gel needed) → dry
electrodes give worse signal than wet
Intracranial EEG and ECoG
- Depth electrodes: are the deepest and most invasive → give the best signal
- Strip electrodes
- Grid electrodes: don’t go through the skull
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller kimvandenbroek83. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.96. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
75632 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now