ERPs and Social Cognition

• The text discusses MEG, EEG, oscillations, and social cognition
• It focuses on ERP approaches for social cognitive and affective neuroscience (SCAN)

Introduction

• ERP methods are optimal for addressing questions central to social cognitive and effective neuroscience (SCAN).
• The article aims to highlight the utility of ERP methods for SCAN-related research.

What are ERPs?

• ERPs are a direct measure of neural activity, coinciding precisely with the activity itself
• fMRI's BOLD signal is an indirect measure.
• Two main classes of ERP waveforms are important for SCAN researchers:
• Stimulus-locked waveform: EEG trials aligned to stimulus onset
• Earlier deflections likely reflect automatic or reflexive psychological processes
• Response-locked waveform: EEG trials aligned to the moment a behavioral response is made

ERP Studies of Social Cognition and Affect

• ERPs are applicable to the study of implicit racial attitudes
• P3/P300/LPP amplitude often increases when a stimulus represents a category different from preceding stimuli.
• Oddball paradigm study: evaluatively inconsistent words evoked a pronounced P3 response, serving as a measure of implicit attitudes
• P3 amplitudes are compared when participants report attitudes toward target objects truthfully/falsely, revealing sensitivity to the true evaluative nature of stimuli, not explicit reports.
• Showing participants white/black faces and positive objects in negative image contexts shows that white faces elicited larger P2 and N2 amplitudes, suggesting more evaluative discrepancy from the negative context.
• A similar P300 pattern was seen among participants reporting highly prejudiced attitudes on the Modern Racism Scale
• ERPs can also to study affective priming mechanisms
• Affective target words are categorized faster when preceded by prime words of the same valence (congruent trials) than opposite valence (incongruent trials).
• "Affective congruency effect" has been replicated, underlying mechanisms are still debated
• P3 amplitude is linked to the magnitude of change in evaluative categorization
• P3 latency is linked to stimulus evaluation time
• Incongruent trials do not elicit larger/slower P3 responses than congruent trials, implying no support for the hypothesis that the affective congruency effect reflects differences in evaluative categorization across trial types.

Theories of Affective Congruency Effects

• Recent theories suggest affective congruency effects arise during the response output process
• Incongruent trials elicit response conflict between the prime-associated response and the target-required response
• Amplitude of the lateralized readiness potential (LRP) should show response activation after prime onset, before the target
• Study: With congruent trials being equally or more likely than incongruent trials, LRP showed that participants initially activated the response suggested by the prime.
• N2, measured after target onset, was larger on incongruent versus congruent trials, aligning with ACC's conflict monitoring function.
• Affective congruency effects result from conflict during the response output stage, not from 'spreading of activation' effects within a semantic network

ERPs and Face Perception

• ERPs have applicability for face perception studies
• The N170 component responds selectively to faces
• It reflects the early configural/holistic encoding of faces in visual perception
• N170 can reveal differences in how individuals perceive others as human
• Research on N170 differences for ingroup/outgroup members shows mixed results, likely due to methodological variability
• N170 study: larger N170 found for ingroup faces compared to outgroup faces under artificial group distinction
• Consistent with research shows people favor own group members and are relatively indifferent to outgroup when intergroup competition is absent and group distinction is arbitrary
• Explicit attention to racial outgroup faces increases N170 responses compared to ingroup faces

Social Categorization

• ERPs play an informative role in the study of social categorization
• Faces are encoded and categorized according to relevant social groups through this process
• ERP responses vary based on a person's gender, starting as early as ~65ms and then at ~165ms in parietal regions
• These early components precede the N170 representing attention to general features of a face predicted by top-down cognitive and attentional processes
• An oddball task was used in a study.
• Race (Black vs White) and gender served as functions of both race
• Gender and race both differentiated very rapidly within 200ms

Stereotyping Studies

• ERPs are applicable to the study of Stereotyping ERPs are recorded while participants read sentences that violated definitional or gender-stereotypical noun-pronoun agreement
• P3/LPP amplitude was enhanced to sentences with definitional and stereotypical incongruities, regardless of participants' overt judgments.
• Similar effects were demonstrated on P3 amplitude during processing of racial stereotype-incongruent trait words in a sequential priming task.
• N400/N4 (sensitive to semantic processes) is larger for sentence-ending words that violate semantic context(‘The pizza was too hot to cry') compared to congruent words ('The pizza was too hot to eat')
• This research investigated whether the N400 is sensitive to violations of semantic social knowledge
• Sentences that, while semantically correct, violated/confirmed gender stereotypes: Larger N400 responses observed when subjects read sentences that.
• Stereotype-based categorizations occur rapidly.
• ERPs made it feasible to study the time course during which such categorizations direct the online comprehension of subsequent info.

Self-Regulation

• ERPs have been used in the study of self-regulation
• Study findings:
  • Utilizing the error-related negativity (ERN) to examine unwanted stereotype-driven response tendencies, the ACC was sensitive for conflict monitoring in racial bias regulation
• Frontal negative slow wave (FSW/NSW) is a late-developing, negative-going deflection reflecting PFC responses supporting regulative control processes. Alcohol intoxication impairs regulative control but not conflict monitoring
• Low-prejudice individuals who are anxious regarding appearing prejudice in front of others have more trouble inhibiting stereotypes than those who do not feel anxious.
• Hypothesis: anxious individuals may be less sensitive to internal conflict monitoring signals associated with racial stereotypes
• Study: Anxious group had smaller ERNs to response conflicts on stereotype inhibition a task which clarified the difference observed in their behavioral control of stereotypes

Neuromagnetism: Tracking Brain Dynamics

• Utilizes Magnetoencephalography (MEG)
• MEG*
• Exploits perpendicular generation of current to measure associated with synaptic activity
• Superconducting quantum interference devices (SQUIDs) are highly sensitive with points placed on scalp
• Magnetic fields from electrically active brain regions reach SQUID via superconducting flux transformer whose shape determines selectivity
• Magnetic fields are sampled across locations making them accurately calculated
• Modern MEG devices use helmet-shaped magnetometers to measure the complete magnetic-field pattern simultaneously without needing to move the instrument
• MEG traces are averaged over many trials to obtain event-related fields (ERFs), similar to EEG

MEG Device Specifications

• Contains 306 SQUIDs at 102 measuring sites
• Each sensor unit has 3 transformers
  • 2 record derivative of magnetic field in x and y directions
  • 3rd measures the z-component
• The MEG instrument is immersed in liquid helium at -269°C.
• Typical strength is femtotesla (10-15T), ten billion times smaller than steady field
• Specialized chamber prevents contamination and ensures accuracy of readings.
  • Special metal shielding and forbidden internal magnetic fields are examples of prevention methods

Neural Currents Underpinning MEG Signals

• Dipolar current is a condition that arises from aligned cortical neurons
• MEG signals come about primarily from these currents

Magnetic Field Direction

• Direction of magnetic flux is determined by current direction of neuron bundles
• Follows the right-hand rule of electromagnetism
• Inverse problem: determining brain currents from magnetic patterns

Calculating Source of Magnetic Fields

• Researchers assume the brain is spherical, active areas are single/multiple current dipoles
• Process:

1. Distribution of measured fields
2. Computer estimates dipole location
3. Computer calculates the expected external magnetic field from these dipoles
4. Computer compares the expected with known field
5. Iterations of process until the 2 match

• Current dipoles are characterized with 5 parameters: 3 for positions (3D), 1 for orientation, 1 for strength.
• Orientation is described using 1 parameter
• Tangential currents to closer surface points produce external magnetic fields
• Other currents cancel
• MEG signals come from cortical fissures
• The position & strength of the dipoles are measured when more than one brain region is active.
• Multidipole models are used to evaluate produced field

Alternative Interpret MEG Data

• A method is to use the minimum current estimate technique
• The technique offers more information while requiring no explicit assumption of brain state

Applications of MEG

• Study sensory inputs
• Signals evoked at particular times when sensory input comes in, these responses are time-locked
• Averaging helps improve signal to noise
• string instrument players exhibit stronger responses in finger area

Cortex-Muscle Coherence

• All cortical regions receiving first impulses have electromagnetic rhythms
• Mu rhythm: frequency components in tactile and movement control

1. 10 hz, linked to touch
2. 20 hz, related to motor functions

• Electrical activity can be measured in muscle to gauge communication speed
• Results:
  • Muscles in hand are faster to respond compared to feet

Action Viewing

• 20 Hz rhythm suppression occurs if a subject moves fingers
• Similar smaller suppression when a person imagines similar movement
• Suppression also occurs when watching other people do same movement

Clinical Applications

• Before neurosurgery application of MEG has been utilized to identify electrical storms in epilepsy discharges

MEG Versus Other Methods

• EEG and MEG have the same stimulus of currents.
• MEG is greater than EEG due to the lack of distortion in measurements of signal from magnetic outputs in tests
• MEG only measures current outputs
• MEG is limited to sulci
  • Radially oriented picked up by EEG
• Best result is a combination of both tests.
  • The magnetic fields generated by the brain are extremely weak
  • SQUIDs in liquid helium allow for accurate environmental manipulation in testing
  • The weak magnetic field gets amplified for processing in testing

High Temporal Resolution

• Using MEG and EEG give full picture of tests, complementary to fMRI and PET.

Electroencephalography

Alpha Waves

• Rhythmic activity oscillating at around 10Hz
• Particularly during relaxed wakefulness and in the absence of sensory stimulation or mental activity

EEG Physiological Basis

• When activated by other neurons via activating electrical potential
• Superficial EPSP and Deep IPSPs contribute to generation of EEG
• Synchronized pyramidal neurons contributes to generation of EEG
• Pyramidal neurons activated from the Subcortal areas contributes to activation

Interactions of Thalamic and Cortical Networks

• Role in EEG activity
• Several neurons that display rhythms generate patterns called Oscillatory.
• The generation of oscillations comes from thalamic stimulation
  • Thalamic oscillation range from 7.5-12.5hz
  • Glucose metabolism in Human is related to thalamic stimulation of EEG through cortical outputs
• The thalamus also produces delta waves
  • These can be interrupted by the ARAS

Synchronization Among Neighboring Neurons

• Large scale is vital cognitive processing.
  • Language processing analyzed through coherence

Normative EEG Activity

• Low frequencies show Large Synchronization
• Large is shown due to higher separation in Neuronal testing
• Adult: Between 10-100 micro volts shown
• Usually between 10-50 micro volts
• Typically delta oscillations are associated with sleep in healthy individuals
• Inverse response exist between normal and pathological conditions
• Delta is primary activity for people ages of 2

Theta

• Diminishes with increasing age.
  • This is similar to other slow activation outputs
• Inhibitatory rhythms
• During wakefulness two types of actions exist

1. Decreased alertness due to scalp distribution
2. Frontal distribution that is associated with stimulus
   • ACC generates theta here

Limbic Regions

• Limbic regions can generate theta by having a gating affect of data processing
• Healthy Individuals have 10 to 45 micro waves
• Alpha rhythms show greater results in posterior area
  • Most common when eyes are shut
  • Alpha Blockage/Desychronization occurs with sudden opening and closing of mental concentration
  • Alpha rhythm also decreases when alertness dips.

Hypotheses

• Various theories that hypothesize stimulation of Alpha waves remain unstudied
  • The brain has shown activity even in the absences of stimulation Gamma Waves EEG activity of 36-44 HZ Associated with cognition, sensory data, and stimulus integration Linked to Gamma increase

Anesthesia

• Systematic sleep related cycle decrease
  • High at wakefulness
  • High in REM
  • Lower in slow waves
• The band possess greatest number of correlation.

Data Acquisition and Signal Analysis

• The placement has been standardized for the past years.

  • Has been expanded now for newer tech

• Uniform coverage needs to be consistent for test to yield accurate reading.

  • Measuring with Vertex can give false data.

• Alpha power is is inversely related to brain activation.

• Spectra provides compositions only on static readings

  • Unable to provide temporal data because the data is shift overtime
    • Use short-time Fourier (STFT) for more data acquisition using Spectrograms.