CHAPTER 5

I. ERPs defined

ERP stands for event-related potential (also, event-related brain potential). Also known as "evoked potentials" (EP) because they are brain responses evoked by discrete stimuli. ERPs vary according to the modality of the eliciting stimulus, so sometimes they are called AEP (auditory evoked potential), VEP (visual evoked potential), or SEP (somatosensory evoked potential).

ERPs are recorded using the same technology as EEG, but they are analyzed quite differently. Whereas EEG is a continuous response that can be seen in "real time," ERPs are discrete responses that are "time-locked" to the eliciting event.

II. Origin of ERPs

Most thought to originate in cortex, where neurons are organized in layers. However, some are known to reflect the neuronal activity at individual brain stem nuclei. In both cases, ERPs represent the activity of large populations of nuerons.

III. Types of ERPs

ERPs are classified according to the stimulus modality, the time scale in which the potential occurs and the variables that affect the potential.

A.Exogenous or sensory - determined mostly by the physical properties of the eliciting stimulus.

1. Brain stem or far field potentials
2. Sensory components and vertex potential

B.Endogenous - determined mostly by the psychological processing demands associated with the eliciting stimulus. Some endogenous potential do not need an eliciting stimulus to be observed. Also called "long latency potentials" and "slow (brain) potentials."

1. P300
2. N400
3. Contingent negative variation (CNV)
4. Readiness (RP) or Bereitschaftspotential

IV. Methodology for obtaining ERPs

A. Averaging vs. single trial analysis
B. Time constant

V. Quantification of ERPs - Extracting components

A. Topography

B. Amplitude

1. baseline-to-peak
2. peak-to-peak
3. area

C. Latency

D. PCA

VI. ERP Paradigms

VII. ERPs and Motor Performance

A. P300 - varies with perceptual demand

B. RP discussed in Chapter 7

VIII. ERPs and Hemispheric Asymmtries
Gennerally larger amplitudes over hemisphere contralateral to stimulus

IX. ERPs During Sleep

A. Brain Stem - no different during sleep

B. Vertex potential - decrease in amplitude with sleep, but N2 occurs early in sleep