Event-Related Potentials (ERPs)

Question 1

What is an ERP and how does it differ to EEG?

Answer 1

ERPs are brain potentials generate by an event. EEGs are the neurological basis for ERPs.

• EEGs give us a way of seeing the CNS’s current level of activation/arousal. Spontaneous activity
• ERPs are an opportunity to understand the specific information about sensory processing. Averaged brain electrical response to a stimulus or cognitive event. Stimuli are presented over many trials. Brain’s response to stimulus is ‘time-locked’ to stimulus presentation

Question 2

What are the ‘components’ of ERPs?

Answer 2

Peaks and troughs.

Question 3

What are the ‘quantifying components’ of ERPs?

Answer 3

• Latency - interval between stimulus onset and peak (in milliseconds). Varies more for endogenous (later processing) than exogenous (early sensory processing)
• Baseline to peak - Voltage difference. how large, in terms of microvolts the peaks are
• Mean amplitude

Question 4

What are the characteristics of ERP components?

Answer 4

Components differ according to:

• Modality stimulated – auditory, visual or somatosensory
• Polarity – positive or negative deflection (Australia positive is down)
• Latency – time that peak occurs
• Scalp topography – variation over different scalp sites
• Experimental manipulation

Question 5

What are the ‘conceptualising components’ of ERPs?

Answer 5

• Exogenous - Early, sensory, automatic, obligatory, no control, linked to external stimulus
• Endogenous - Later, cognitive, controlled, linked to the processing of external stimuli

Question 6

What is BAEP (brainstem auditory evoked potential)?

Answer 6

Basic primary test for the integrity of the auditory system. Mapping information going through all of the processing levels.

Question 7

Explain the sensory system processing of ERPs.

Answer 7

• Brain stem evoked potential (0-10ms) - auditory nerve to cortex activation
• Sensory ERPs - (50-200ms), primary cortex activation.
  Components generated in primary cortical sensory areas (auditory, visual, somatosensory)
• Long-latency potentials - (250-750ms), frontal and parietal association cortex, hippocampus and amygdala. Motor potentials - pre-central (motor) cortex at hemisphere opposite the moving limb

Question 8

List some of the advantages of ERPs.

Answer 8

• Temporal resolution in milliseconds
• Increasingly, spatial resolution
• Relatively low cost
• Administration is simple - non-invasive, no confined spaces or radio-active substances

Question 9

What is inhibition and how do we evoke it?

Answer 9

Inhibition is the conscious restraint of a behavioural process, the ability to withhold a planned response. Inhibition processes are generated in the frontal lobe.

We can evoke an inhibition response through a Go-NoGo task. This task requires the subject to withhold responding to infrequent NoGo stimuli presented among Go stimuli.

Question 10

Explain the N2 component.

Answer 10

The N2 is a large deflection in waveform ~200ms. It occurs to stimuli requiring restraint or inhibition. It is a neural basis for the overt inhibition seen in the task.