1. Implications of Event Related Potentials in Clinical research
Dr Arun Sasidharan MBBS, PhD
Senior Research Officer & Research Program Manager
Axxonet Brain Research Laboratory (ABRL)
Axxonet System Technologies Pvt. Ltd., Bengaluru
Presentation for: N-CORTEX – 2017 on Jan Dept. of Psychology, Mount Carmel College, Bengaluru

2. Structure of the talk Simplify the concept and technique of ERP
Quick overview on different types of ERPs
Walk-through the design of simple ERP tasks
Structure of the talk

3. Structure of the talk Simplify the concept and technique of ERP
Quick overview on different types of ERPs
Walk-through the design of simple ERP tasks
Structure of the talk

4. What is ERP? – simplistic view
ERP – Event Related Potential
They are tiny fluctuations in a person’s EEG, related to a stimulus presentation or an event occurrence.
ERPs are informative about the exact timing of cognitive processes

5. Why ERPs?
Most assessments in mental health involve subjective component
ERPs can provide more objective assessment of brain function
ERPs can tap into brain functions at very high temporal resolutions
Can be set up in most clinics??

6. EEG setups – So easy!! 1 2 3

7. Post-synaptic potentials generate EEG/ERP
How are ERPs generated?
Post-synaptic potentials generate EEG/ERP
Not Action potentials
Prof. Gilley;

8. How are ERPs derived? - concept
Task-relevant brain processes are time-locked to the task events
Averaging EEG portions or epochs that are time-locked to events
Identify task relevant brain processes in terms of size & latency of the resulting waveforms - ERPs

9. How are ERPs derived?
Stimulus
Source:

10. How are ERPs derived?
Source:
An Introduction to the Event-Related Potential Technique by Steven J. Luck

11. How are ERPs derived?
Raw EEG

12. How are ERPs derived?
Raw EEG
Cleaning

13. How are ERPs derived? Raw EEG Cleaning Epoching 1500ms 1500ms 1500ms

14. How are ERPs derived? Raw EEG Cleaning Epoching Trial 1 Trial 2

15. How are ERPs derived? Raw EEG Cleaning Epoching ERP 1500 ms Trial 1
Event related potential
ERP

16. Exploring the ERP time window
Methods…
Exploring the ERP time window
Check if individual subject data are correctly detected
Start with all subject grand average
Modify to fit all data

17. What causes ERPs? + + + Phase-locked evoked potentials
Phase-reset spontaneous oscillations
Non phase-locked induced potentials + + +
Turi et al. NeuroImage 59 (2012) 2607–2624

18. Structure of the talk Simplify the concept and technique of ERP
Quick overview on different types of ERPs
Walk-through the design of simple ERP tasks
Structure of the talk

19. Temporal relation in ERP
Prof. Gilley;

20. P50 sensory gating CNT Standard S1 CNT Standard S2 SCZ Standard S1
P50 suppression
N1-P2 suppression
Measurement time-window
Measurement parameter
Electrodes analysed
Number of epochs analysed
Negative peak in -100ms to 0ms;
Positive peak (P50) in 20ms to 90ms
Ratio of peak to peak amplitude difference between second of the standard tone-pair and first one.
FCz & Cz
SCZ: ± ( )
CNT: ± ( )
t statistic = 1.032; p-value = 0.325; CI = -4.3 to 22.6
Negative peak (N1) in 60ms to 170ms;
Positive peak (P2) in 140ms to 250ms
Ratio of peak to peak amplitude difference between second of the standard tone- pair and first one.
FCz & Cz
CNT Standard S1
CNT Standard S2
SCZ Standard S1
SCZ Standard S2

21. Measurement time-window Measurement parameter
auditory sensory memory
MMN
Measurement time-window
Measurement parameter
Electrodes analysed
150ms to 250ms
Mean amplitude difference between first of the standard tone-pair and first of deviant tone-pair.
FCz & Cz
CNT Standard S1
CNT Deviant S1
SCZ Standard S1
SCZ Deviant S1
Thought to reflect automatic comparison of incoming stimuli to a sensory memory trace of preceding stimuli

22. structural encoding of faces
Negative potential at lateral occipital sites with a peak at approximately 170 ms
More for face than non-face stimuli; highly familiar non-face stimuli also show high N170
Image source: Kuefner et al. 2010

23. Attentional shift
N2pc
It is the relatively greater negative deflection observed at posterior electrode sites contralateral to the location of a target visual stimuli
It reflects the focusing of spatial attention onto the target location
Image source:

24. Measurement time-window Measurement parameter
Error monitoring
ERN
Measurement time-window
Measurement parameter
Electrodes analysed
-60ms to 60ms
Mean amplitude difference between correct and incorrect responses
Fz & FCz
CNT Correct
CNT Incorrect
SCZ Correct
SCZ Incorrect

25. Measurement time-window Measurement parameter
automatic attention and contextual updating of working memory
P300
Measurement time-window
Measurement parameter
Electrodes analysed
250ms to 450ms
Difference in area under the curve (only positive side) between frequent and rare images
Cz & Pz
CNT Frequent Passive
CNT Rare Active
SCZ Frequent Passive
SCZ Rare Active
Elicited by unpredictable, infrequent changes in ongoing stimuli
Usually tested using “Odd-ball” paradigm; more for rare than frequent stimuli

26. Readiness Potential (RP) & Lateralized Readiness Potential (LRP)
RP: Mean of Negative deflection between & 0 ms
LRP (for Rt hand): Lt RP – Rt RP
More negative when contralateral hand prepares
Reflects movement preparation
At FC3, FC4, C3, C4, CP3, and CP4
Rt RP
Lt RP
Baseline
Baseline
Image source: Nature Reviews Neuroscience 6,   (March 2005) doi: /nrn1630

27. Clinical implication of ERPs
ERP Deficits in Schizophrenia
↓P50 suppression
(sensory gating)
[Adler et al., 1982; Freedman et al., 1983; Bramon et al., 2004]
↓N100
(auditory discerning)
[Rosburg et al., 2008]
↓MMN
(auditory sensory memory)
[Nȁȁtȁnen at al., 2009]
↓P300 (automatic attention & contextual updating of WM) [Bramon et al., 2004; van der Stelt at al., 2005]
↓P100 (global processing of visual perception) [Foxe at al., 2001; Butler at al., 2007; Yeap et al., 2008]
↓N170 (structural encoding of faces) [Campanella et al., 2006; Caharel et al., 2007; Obayashi et al., 2009; Lee et al., 2010]

28. Structure of the talk Simplify the concept and technique of ERP
Quick overview on different types of ERPs
Walk-through the design of simple ERP tasks
Structure of the talk

29. Basic ERP Acquisition setup
Stimulus Presentation
EEG Acquisition
Event Markers
Paradigm design software
ERP analysis software

30. Define condition requirements
E.g. For P300 ERP:
Basic requirement? Unpredictable and rare presentation of stimulus; Or having implicit salience
Need to attend to stimulus? Yes
Need to respond to stimulus? Preferable; Not necessary
Which modality? Any; Mostly auditory or visual

31. Define condition requirements
E.g. For P300 ERP:

32. Uniformity in subject engagement
Adequate breaks
Divide into smaller blocks
Blink holidays
Feedbacks

33. Balance stimulus parameters
Auditory: Loudness, duration, complexity
Visual: luminance, size, duration, colour, visual frequency
Lower spatial frequency (1 cycle/degree)
Higher spatial frequency (2 cycle/degree)
Colour image
Two-tone image

34. Balance stimulus parameters
Visual: visual angle

35. Complex designs…yet simple tasks
80% Standard paired tones
1000Hz, 15ms long, 500ms apart
20% Deviant paired tones
1500Hz, 15ms long, 500ms apart
1200ms to 1900ms
240ms
Pre stimulus Mask
Visual distracters (can be at top or bottom)
240ms OR OR
Target stimulus (can be at left or right) OR OR
460ms
Response window of 700ms OR OR OR
0-100ms
60ms
Triangle
present
Triangle
absent
Face
present
Face
absent
Auditory distractors
200ms
Post stimulus Mask
0-600ms
Fixed duration
Random duration
Nair AK, Sasidharan A, John JP, Mehrotra S, Kutty BM. Assessing neurocognition via gamified experimental logic: A novel approach to simultaneous acquisition of multiple ERPs. Front Neurosci. 2016;10(January):1–14.

36. Thank you