Neuroimaging for Cognitive Research

January 10, 2018 | Author: Anonymous | Category: Science, Biology, Neuroscience
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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 Functional

Structural MRI X-ray

fMRI

SPECT PET

CT/CAT

EEG

ECG

Electro-Encephalograghy (EEG) • Electrical current originating in the cortical areas • Measured across scull and tissue - adjustments for physical properties -

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current

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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current

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. Noncompositional 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 (350500ms) sensitive to complement coercion • M350 component in the left temporal area is sensitive to semantic anomaly • Consistent with ERP findings for N400 component

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