W4: Electroencephalography (EEG)

What is an EEG and how does it measure brain activity?

EEG (Electroencephalography) is a non-invasive technique that measures the electrical activity of large populations of neurons via electrodes placed on the scalp.

Who is Hans Berger and what is his significance in EEG?

Hans Berger is known for discovering that electrodes placed on the scalp can measure changes in electrical activity in the brain, marking the birth of EEG.

What is the purpose of digitization in EEG recordings?

The process of converting an analogue EEG signal into a discrete set of samples that can be stored and analyzed on a computer.

What does the 10-20 system refer to in EEG?

The 10-20 system prescribes the location of each EEG electrode on the scalp according to distances from specific anatomical landmarks.

What are the three scales of neuronal organization?

Microscopic scale, which reflects single neurons; Mesoscopic scale, which reflects populations of cortical neurons; & Macroscopic scale, which reflects large regions of the cortex.

What is the primary recording characteristic of EEG?

EEG is characterized by rhythmic brain waves oscillating at various frequencies, depicting activity from multiple neural sources over time.

What is the process of event-related potentials (ERPs)?

ERPs are derived from EEG recordings by averaging segments time-locked to specific events to isolate the neural activity related to those events.

What is power in EEG analysis?

The amount of energy in a frequency band, measured as the squared amplitude of the oscillation.

What are the main advantages of using EEG in clinical neuroscience?

EEG offers superior temporal resolution, reflects biophysical phenomena of neural populations, and provides a multidimensional signal including time, space, frequency, power, and phase information.

List two significant limitations of EEG.

EEG has low functional localization capabilities and is not suitable for investigating activity from deep brain structures.

What are Event-Related Potentials (ERPs)?

ERPs are changes in EEG that occur in response to specific sensory, cognitive, or motor events, revealing the neural activity associated with those events.

What is the significance of latency in ERP components?

Latency refers to the time taken for an ERP component to appear after the event, indicating how quickly the brain processes the stimulus.

Define coherence in relation to EEG signals.

Coherence measures the consistency of the relationship between the frequency components of two or more EEG signals, indicating their functional connectivity.

What is independent component analysis (ICA) in EEG processing?

ICA is a statistical technique that separates multivariate EEG signals into independent subcomponents, helping to identify and remove artifacts.

What do power-line artifacts refer to in EEG data?

Power-line artifacts are electrical noise originating from mains electricity, which can contaminate EEG recordings.

What are neural oscillations?

Rhythmic or repetitive patterns of electrical activity in the brain, often categorized into different frequency bands.

How is the amplitude of EEG waves measured?

Amplitude can be measured as peak-to-peak (difference between positive and negative peaks) or peak amplitude (deflection from zero).

What do the frequency bands alpha (10 Hz), theta (4-8 Hz), and gamma (>30 Hz) signify in EEG?

Alpha waves are associated with relaxation, theta waves are linked to drowsiness and memory processing, while gamma waves are involved in attention and cognitive processing.

What is the purpose of digital filtering in EEG preprocessing?

Digital filtering is used to attenuate or eliminate unwanted frequencies, such as power-line noise, from the EEG signal.

What is the difference between event-related oscillations that are induced and those that are evoked.

Induced oscillations are not time-locked to a stimulus while evoked oscillations are time-locked and closely related to event-related potentials.

What is phase-locking in EEG analysis?

Phenomenon that occurs when the phase of oscillations in different brain areas consistently relates over time, indicating a degree of coordination between regions.

What is spectral analysis?

Primary method for quantifying brain waves in EEG by breaking down the EEG signal into its constituent frequencies.

What is the difference between Fast Fourier Transforms (FFTs) and Wavelet transforms?

FFTs break down signals into sine and cosine waves with fixed frequency bands, while wavelet transforms provide flexibility in frequency resolution at various scales.

What is inter-trial coherence in EEG?

The consistency of phase locking of the signal at the same electrode across successive trials of a stimulus presentation.

What does re-referencing in EEG entail?

Re-referencing is changing the reference electrode used to calculate voltage differences in the EEG signal, which can affect interpretation outcomes.

What are the implications of conducting EEG in a non-electrically shielded environment?

Conducting EEG in non-electrically shielded environments increases the likelihood of artifacts, such as power-line noise, affecting data quality.

What is the significance of the average reference technique in EEG?

Average reference technique involves referencing each electrode's signal to the average of all electrodes, which helps in highlighting localized activity.

How does muscle activity contribute to EEG artifacts?

Muscle activity, such as clenching teeth or frowning, generates high-frequency noise, contaminating the EEG signal.

What is the role of electrode conductive gel in EEG recordings?

Electrode conductive gel facilitates better electrical conductivity between EEG electrodes and the scalp, thus improving signal quality.

Define the term 'impedance' in the context of EEG.

Impedance refers to the opposition to the flow of electrical current; low impedance between the scalp and electrodes is necessary to reduce noise.

Identify two main advantages of using ERPs in research settings.

ERPs offer high temporal precision and are well-suited for investigating differences in brain processing between conditions.

What are 'background activities' in the context of ERP averaging?

Background activities refer to non-phase-locked brain activity that is averaged out during ERP recording, as it may cancel itself out across trials.

What anatomical landmarks guide electrode placement in the 10-20 system?

Electrode locations are determined based on distances from anatomical landmarks such as the nasion, inion, and preauricular points.

What is Event-Related Synchronization (ERS)?

ERS refers to increased synchronization of brain oscillations resulting from stimulus presentation, indicating heightened neural processing.

What do peaks in EEG spectra indicate?

Peaks in EEG spectra indicate the dominant frequencies present in the EEG signal, providing insight into the brain's oscillatory activity.

What is the relationship between amplitude and power in EEG signal?

Power is mathematically related to amplitude; specifically, power is the squared amplitude of the oscillation.

What challenges does EEG face in terms of spatial resolution?

EEG spatial resolution is inherently limited, meaning it struggles to precisely locate the source of brain activity compared to methods like fMRI.

What is the relationship between phase and frequency in EEG analysis?

Phase refers to the relative timing of a wave, while frequency indicates how quickly oscillations occur (cycles per second).

What are common sources of muscle artifacts in EEG recordings?

Common sources include contractions from scalp, neck, and facial muscles, which create high-frequency noise in the EEG.

What do time-frequency plots illustrate in EEG analysis?

Time-frequency plots extend spectra to show how power in different frequency bands changes over time, making them useful for event-related analysis.

Describe the significance of the polarity in ERP components.

Polarity dictates whether a component is characterized as negative (N) or positive (P), indicating the direction of voltage change related to events.

How do sweat artifacts affect the EEG readings?

Sweat artifacts introduce low-frequency fluctuations due to changes in skin impedance, impacting the quality and clarity of EEG signals.

What is the purpose of a Laplacian reference in EEG?

A Laplacian reference subtracts the average of surrounding electrodes from a central electrode, providing a more localized measure of cortical activity.

What is one limitation of scalp electrodes?

They are unable to distinguish between excited or inhibitory input.

What is phase?

The amount of energy in a frequency band, measured as the squared amplitude of the oscillation.

What are epochs?

Time-locked segments of experimental events of interest.