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Neuroimaging for Cognitive Research

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).

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Neuroimaging for Cognitive Research

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  1. Neuroimaging for Cognitive Research

  2. 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)

  3. Imaging Approaches Functional Structural MRI fMRI SPECT X-ray PET CT/CAT EEG ECG

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

  5. EEG • Strengths: • Relatively easy to administer and cheap • High temporal resolution (miliseconds) • Weaknesses • Hard to interpret (noise, artifacts) • Low spatial resolution

  6. 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

  7. ERP temporal resolution From: brainvat.wordpress.com

  8. ERP spatial resolution

  9. 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)

  10. 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

  11. ERP components P1 N1 P3 N400 P600 P2 N2

  12. P1/N1 • P1 • 50ms – auditory, 100ms – visual • General attention/arousal • N1 • Selective attention to stimulus characteristics • Stimulus discrimination

  13. 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

  14. P3 • Stimulus classification and response preparation • Varies with stimulus complexity • Possibly associated with memory and attention

  15. N400 • Sensitive to language (not music) specific anomalies • Semantic but not syntactic processing • May reflect the degree of anticipation/preactivation From Kutas & Hillyard 1980

  16. 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)

  17. 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

  18. + - current

  19. MEG • Strengths • High temporal resolution • Weaknesses • Sensitivity to magnetic interference • Hard to administer • Hard to interpret (noise, artifacts)

  20. MEG and synchronous cognitive networks

  21. 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

  22. 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

  23. Sources of Neural Response

  24. 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

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