VL5 Methods 2

Electroencephalography

• Measures changes in potential

• Large amounts of neurons have to be activated (hundreds of thousands)

• pass through various tissue —> most often pyramidal cells

• Postsynapctic activity at dendrites or cell body

• Electric activity behaves like electricity

• Potential difference measured by comparing to reference electrode Often: nose, mastoid bones behind ear, chest

• Choice of reference electrode influences the signal

• Influences Amplitude & Scalp Topographic Distribution

  
  

• Signal has to pass through various types of tissue à therefore most often pyramidal cells

• IPSPs & EPSPs is measured —> indistinguishable, which of both it is

temporal resolution

• highly sensitive electrodes 32 to 256

• attached to head using electrode cap

  • standardized positions

    • 10-20 system

    • extended 10-20 system

• conductive gel/saline solution: increased skin conductivity

• amplification & digitization of signal

• active eeg electrodes measured against reference electrode —> reference electrode picks up as little brain activity as possible

• offline data analysis

• simultaneously measured to monitor muscle artifacts from eye movements

  • EOGV vertical

  • EOGH horizontal

  • muscle activity is stronger than brain activity!

• amplitude —> how strong

• frequency —> number of oscillations per second

  • five physiologically relevant bands

• Delta —> deep sleep

• Theta: falling asleep & high concentration

• ALpha: relaxed, awake, especially closed eyes

• beta: mental or physical activity

• Delta: 0,5-3 Hz

• Theta: 4-7 Hz

• Alpha: 8-13 Hz

• Beta: 14-30 Hz

• Gamma: >30 Hz

The more calm: slower (low frequency) and high amplitude

• Raw EEG is averaged

  • averaged background EEG

  • averaged Evoked Potential

• external and internal events can evoke changes

=Components

• P1: early component around 100 milliseconds after visual stimulus.

• N1: early component occurring around 100-200 milliseconds, associated with initial sensory processing.

• P2: Higher-order sensory processing and feature detection.

• N2: Cognitive control & conflict monitoring.

• P3 (P300): peaking around 300 milliseconds attention and decision-making processes.

• Polarity

• Latency

• Distribution over the scalp

• amplitude

• time between start of stimulus and peak of component

• Sequence —> what order the components appear in

• exact timing —> The specific latency values of different ERP components.

• difference between adjacent extremes

• difference between baseline and peak

1. Pre-processing

2. Epoch selection, baseline correction

3. averaging, subtraction, grand averaging

4. visualization

5. selection of channels, roi, time windows

6. statistical analysis - t-test, ANOVA, Regression

7. further analyses e.g. source localisation —> source imaging can combine eeg & mri

• automatic artifact correction

• manual artifact correction

• filtering —> getting rid of signal drift

• Brain vision analyzer

• BESA

• matlab based:

  • eeglab

  • erplab

  • fieldtrip

• Mne-python

• Magnetoencephalography

• use Magnetometers to measure magnetic currents

• cooled down to extremely low temperatures w/ liquid helium —> more sensitivity

• makes use more challenging

• active neurons generate small magnetic fields due to flow of electricity

• better localization of signals: magnetic field passes through tissue without resistance

• but nevertheless a bit weaker for deeper brain structures

• radial sources invisible in MEG, only tangential sources produce measurable signal

• evoked potentials

• latency = <100 ms

• sensory analysis of stimuli

• directly follow perceptual stimulus

• dependent on physical sitmulus properties

• no influence by psychological variables

• Latency >100 ms

• less closely tied to stimulus

• co-vary with psychological factors

  • surprise

  • recognition

• e.g. p300 component

• Mismatch negativity

• p300

• slow potential shifts

• measured by oddball paradigm

  • frequent standard tones with rare deviants up to 20%

• mismatch negativity = Deviants-standard

  • reflects brain’s automatic detection of deviation from established pattern

• requires no attention for standard tones

• detection of rare target stimuli

• after sensory processing —> around 300 ms —> positive deflection of eeg signal —> attention

• contingent negative variation

  • observed between a warning signal & expectation of an external stimulus

• motor ERPs

  • directly precedes a motor act

  • appear esp. over motor cortex

  • libet experiment —> unconscious brain activity in preparation before conscious intention to move

—> Frequency analysis of the eeg

• frequency distribution

• power

• power spectrum

• proportion of different frequency bands in specific temporal window

squared amplitude

• strength of an individual frequency value

• shows power(energy) in total signal

• as a function of frequency at given time point

• brain imaging -> not necessarily causality

• shows involvement of brain region in cognitive processes

• shows involvement of brain regions associated with ERP component for specific cognitive processes

  
  

• reversible brain stimulation methods

• e.g. tms

• voxel-based morphometry

• diffusion weighted MRI/diffusion tensor imaging

• functional near-infrared spectroscopy fNIRS

• TDCS

• Eye tracking, pupillometrie

• genetic& endocrinologic methods

o   neuroimaging analysis method

o   compares local concentration of gray matter across entire brain

o   commonly used to detect structural brain changes related to psychiatric conditions + aging processes

o   taxi driver study

o   study the diffusion of water molecules in biological tissues in brain

o   insights into microstructural properties of tissues

o   investigation of brain connectivity and integrity

functional near-infrared spectroscopy

• non invasive

• measures changes in hemoglobin concentration

• cerebral blood flow through absorption of near-infrared light by hemoglobin

• transcranial direct current stimulation

• electric current modulates neuronal activity