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PSYC3039 Introduction to Cognitive Neuroscience. Weeks 4 and 5: Introduction to Cognitive Electrophysiology.

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psyc3039 introduction to cognitive neuroscience

PSYC3039 Introduction to Cognitive Neuroscience

Weeks 4 and 5: Introduction to Cognitive Electrophysiology

slide2

Case study: Selective attentionAlternative reading to Naatanen, 1992:Naatanen, R (1990) the role of auditory information processing as revealed by event-related potentials and other measures of cognitive function, Brain and Behavioural sciences 13: 201-232 (peer commentary 232-288)

sources of the p1 and n2
Sources of the P1 and N2
  • PET source of the P1 and N2 in ventromedial posterior fusiform gyrus (FG) and middle occipital gyrus (MOG), respectively
  • ERPs show activation on scalp over these regions
  • Dipole modelling with simulated sources in the FG and MOG produce simulated scalp activations that match the empirical data very well
the n1 and nd components of the auditory erp
The N1 and Nd components of the auditory ERP
  • N1 and selective attention
  • The negative difference wave (Nd)
    • onset 60-80ms
    • endures 300-400ms
the effects of discriminative difficulty on the auditory nd

Difference waves

50

100

400

Increasing amplitude

Earlier onset

Longer duration

Decreasing

discrimination

difficulty

The effects of discriminative difficulty on the auditory Nd

TASK INSTRUCTION

Attend Low/High

Ignore High/Low tones

multiple sources of the nd
Multiple sources of the Nd
  • ISI manipulation of N1 selective attention paradigm exposes multiple sources of Nd
  • Frontal and central sources
naatanen s processing negativity theory
Naatanen’s Processing Negativity theory

GOOD

MATCH

PROCESSING

NEGATIVITY

FURTHER

PROCESSING

naatanen s processing negativity theory1
Naatanen’s Processing Negativity theory

BAD

MATCH

PROCESSING

NEGATIVITY

FURTHER

PROCESSING

naatanen s processing negativity theory2
Naatanen’s Processing Negativity Theory
  • Processing Negativity: PN
    • Model incorporates exogenous N1/P2 effects
    • PN concurrent with N1/P2 and reflects stimulus:model comparison process
  • Negative Difference Wave: Nd
    • Reflects the difference over trials between PN to relevant and irrelevant stimuli
    • The smaller the difference, the smaller and later the Nd
  • N1
    • Amplitude attenuates with stimulus repetition – hence smaller overall when difference between relevant and irrelevant stimulus small

Relative difference between stimulus and trace

summary n1 and attention
Summary: N1 and attention
  • Exogenous N1 reflects pre-conscious, stimulus detection; source in modality specific cortex
  • Attention imposes a slow wave - the Nd, with frontal and central sources
  • Nd occurs early (~70ms) and reflects top down, cognitive control of physical selection
  • Nd sensitive to difficulty of discrimination
  • Processing Negativity theory accounts for phenomena
detection of significant events in environment

Regular (standard) stimulus

New (deviant) stimulus

“MMN”

Detection of significant events in environment

When the brain detects some change in the environment (marked by MMN), the brain must work out if the new event needs attention – is it a threat; is some action required? If so, further (attentional) processing is marked by the N2 and P3a and P3b ERP components

the p3 component and attentional processing of significant events

Regular (standard) stimulus

New (deviant) stimulus

“MMN”

The P3 component and attentional processing of significant events
  • Details
    • Latency: 300-500ms post-stimulus
    • Requires conscious attention
  • Frontal P3
    • detection and entry of novel stimuli into consciousness
  • Parietal P3
    • evaluation of significance
    • context assimilation
    • correlates with response time
  • Late slow waves
    • context & related working memory updating/maintenance
p3 abnormalities ubiquitous in psychopathology
P3 abnormalities ubiquitous in psychopathology
  • Post-traumatic stress disorder
    • Parietal P3 reduced
    • Abnormal LSW
  • Panic Disorder
    • Frontal P3 enhanced

Fz

Cz

Pz

eog

preparatory processing
Preparatory processing
  • Contingent negative variation (CNV): 500-1000ms pre-stimulus: expectancy and preparation for event
  • Motor potential and Bereitschaftspotential: 1-2 secs preceding response

Bereitschaftspotential

erps and stages of processing
ERPs and stages of processing
  • N400
    • about 400ms post-stimulus
    • Semantic incongruity
    • Size affected by degree to which meaning of sentence is derived over sequence of words in sentence

Bereitschaftspotential

summary of components discussed
Summary of components discussed
  • Automatic processes (obligatory cortical mechanisms)
    • P50: automatic feature analysis
    • N1: automatic detection of stimulus
    • MMN: automatic detection of stimulus change
  • Controlled processes (working memory)
    • Nd: controlled selective attention to stimulus
    • N2b (frontal): stimulus categorisation
    • P3a (frontal): conscious awareness of novelty
    • P3b (parietal): evaluation of stimulus significance
    • N4: contextual processing of language
    • Late slow waves: updating of working memory content
    • CNV and Motor potential : preparatory processing for future events
general summary
General summary
  • Stages of processing
  • Visualisation of non-behavioural processes
  • Multiple components
    • Endogenous vs exogenous components
    • Modality specific vs non specific components
    • Specific topographies
    • Parallel distributed processing
  • Uses in psychopathology
  • Source localisation issues
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