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Neuroimaging for Cognitive Research

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Presentation on theme: "Neuroimaging for Cognitive Research"— Presentation transcript:

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

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

5 EEG Strengths: Weaknesses 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 ms - phonological/syntactic ms - conceptual/semantic

7 ERP temporal resolution

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

13 P2/N2 P2 – obligatory cortical potential N2
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 Urban noise 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


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

21 MEG and synchronous cognitive networks

22 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

23 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

24 Sources of Neural Response

25 Results Anterior Medial Field response ( ms) 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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