Neural Time Series Data Types

EEG (electroencephalogram) measures electrical activity through field changes.

  • Scalp EEG: Non-invasive, resembling wearing a cap on the head.
  • iEEG (intracranial EEG): Invasive, requires a craniotomy.
  • Stereotactic EEG / Depth electrode: Embedded deep within brain tissue.
  • ECoG (electrocorticogram): Surface-level measurement on the brain cortex.
  • MEG (magnetoencephalogram): Measures magnetic field changes.
  • fMRI/PET: Measures blood flow changes, typically using BLOD.
  • LFP (local field potential)
  • Spike (single unit)

EEG Variants

Image Name

EEG Variants

Characteristics of EEG

Advantages and Disadvantages

Advantages

  1. EEG has high time resolution, ideal for studying rapidly occurring neural activities like cognitive, perceptual, linguistic, emotional, and motor processes.
  2. Reflects neural activity directly from the brain cortex.
  3. Captures multidimensional data: time, space, etc.

Disadvantages

  1. Not suitable for studying deep brain regions.
  2. Not optimal for pinpoint accurate research.
  3. Inadequate for research requiring extremely high time precision due to constantly changing brain states.

For detecting high-frequency activity above 60Hz, MEG is preferable over EEG.

Units

  • EEG unit: Typically measured in volts, in millivolts (mVmV) or microvolts (μV\mu V).
  • MEG unit: Usually measured in tesla, in femtotesla (fTfT), equal to 10−1510^{-15}.

Oscillation in EEG

Name Frequency Range (Hz) Location Remarks
Delta <4 - Non-REM sleep
- Children
- Continuous attention tasks
Theta 4-8 - Common in infants
- Drowsiness in adults and adolescents
- Attempting to suppress instinctive responses
- Stage 1 sleep
Alpha 8-12 - Relaxation
- Eyes closed
- Long-distance communication across brain areas
Mu (SMR) 8-13 - Also called sensorimotor rhythm (SMR)
- Autism
- Rest-state motor neurons
Sigma 12-16 - Non-REM sleep → Memory consolidation
Beta 15-30 - High mental activity: Attention concentration, high alertness, anxiety
Low Gamma 30-80 - Multi-sensory, consciousness
- Short-term memory
High Gamma 80-150 - Emotion
Ripples 80-250 - HFO (high-frequency oscillations) → Often associated with diseases like epilepsy
Fast Ripples 250-500 - HFO (high-frequency oscillations) → Often associated with diseases like epilepsy

Note: There is no unified definition for frequency ranges in academic literature, and different sources may present different ranges.

ERP vs Time-Frequency Based Approach

ERP

ERP (Event-Related Potentials) is obtained by averaging EEG signals from multiple repetitive events to eliminate noise irrelevant to events. An example is the P300, a positive wave occurring approximately 300ms after a surprising event.

However, time-locked but non-phase-locked activities result in information loss after ERP averaging. For example, the amplitude values obtained by averaging with ERP (second column in the image below) gradually disappear due to the positive and negative overlays from different trials. Calculating power, on the other hand, shows noticeable frequency growth.

ERP Illustration

Time-Frequency Based Approach

This approach is useful in obtaining information about oscillations.

Topographical Localization

Topography typically displays electrode positions, as shown in the image below:

Topographical Localization

10-20 System

The 10-20 system is an international standard for EEG electrode placement. The numbers 10 and 20 indicate the distances between adjacent electrodes, being 10% or 20% of the total anterior-posterior or left-right distances of the skull, as shown below:

10-20 System

Electrode Placement

Time-frequency Result

Time-Frequency Result

Excellent Reference Materials

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