Neuroimaging for Cognitive Research

Obtaining evidence from the Brain

•  Lesion studies (ling. aphaisiology) •  Neuroimaging (CT, PET, SPECT, fMRI, EEG,

MEG) •  Direct manipulation

–  cell recordings (single and array) –  electrical stimulation –  neurochemical stimulation (barbiturates - Wada)

Imaging Approaches

Structural Functional

X-ray MRI

CT/CAT

fMRI

PET

SPECT

EEG ECG

Electro-Encephalograghy (EEG)

•  Electrical current originating in the cortical areas •  Measured across scull and tissue - adjustments

for physical properties

current

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EEG

•  Strengths: – Relatively easy to administer and cheap – High temporal resolution (miliseconds)

•  Weaknesses – Hard to interpret (noise, artifacts) – Low spatial resolution

EEG signal analysis

•  Event Related Potentials (ERP) •  Electrical activity on an electrode or a group

of electrodes averaged over many trials •  Positive and negative peaks at different

points in time from the stimulus presentation •  0-150 ms - perception •  150-350 ms - phonological/syntactic •  350-600 ms - conceptual/semantic

ERP temporal resolution

From: brainvat.wordpress.com

ERP spatial resolution

ERP caveats

•  Signals from multiple sources (general body function unrelated to cognition) – Multiple presentations of the stimuli

•  Uncertainty of the signal source – Multiple “dipoles” may be responsible for

the strength of signal at a given location – Source can be verified with other imaging

methods (e.g., PET)

ERP components

•  Three dimensional representation – Direction: Negative vs. Positive deflection – Latency: time from stimulus onset – Gross location: frontal, temporal, occipital,

etc. •  P1, N1, P2, N2, P3, N400, P600

ERP components

P1 N1

P2 N2

P3 N400 P600

P1/N1

•  P1 – 50ms – auditory, 100ms – visual – General attention/arousal

•  N1 – Selective attention to stimulus

characteristics – Stimulus discrimination

P2/N2 •  P2 – obligatory cortical potential

–  Low individual variability and high reproducibility –  Stimulus classification –  Sensitive to pitch and loudness (auditory)

•  N2 –  Stimulus discrimination –  Deviation of stimulus from expectation

P3

•  Stimulus classification and response preparation

•  Varies with stimulus complexity •  Possibly associated with memory and

attention

N400 •  Sensitive to language (not music) specific anomalies •  Semantic but not syntactic processing •  May reflect the degree of anticipation/preactivation

From Kutas & Hillyard 1980

P600

•  Memory and language – Old-new response (greater for old

information) – Syntactic Positive Shift (Kutas and Hilliard,

1983) •  Syntactic processing load due to parsing failure •  Elicited with syntactic and morphosyntactic

violations (agreement, phrase structure, subcategorization, syntactic ambiguity)

Magneto-Encephalography •  Similar to EEG in some respects •  Detects very weak magnetic fields resulting from electrical

activity –  Earth - 1010

–  Urban noise - 1010

–  Epileptic spike - 1,000 –  Sensory evoked response - 100

•  Tens of thousands of neurons firing in the same direction •  Detected with Superconducting Quantum Interface Device

(SQUID) •  Orthogonal to EEG •  Dipole source model

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MEG

•  Strengths – High temporal resolution

•  Weaknesses – Sensitivity to magnetic interference – Hard to administer – Hard to interpret (noise, artifacts)

MEG and synchronous cognitive networks

Use Case: Study of Silent Meaning

•  Pylkkanen and McElree (JCN, 2007) •  Semantic Compositionality

– Strict/compositional version – semantics are always expressed in syntax

– Alternative version – some semantic interpretations are non-compositional – independent of syntax

Compositional vs. Non-compositional Meaning

•  The author began the article – Activity (writing) is implied –  “Coerced complement”

•  The author wrote the article – Activity is explicit

•  The author astonished the article – Semantically anomalous

Sources of Neural Response

Results

•  Anterior Medial Field response (350-500ms) sensitive to complement coercion

•  M350 component in the left temporal area is sensitive to semantic anomaly

•  Consistent with ERP findings for N400 component