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

EEGECG

Electro-Encephalograghy (EEG)

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

properties

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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

P1N1

P2N2

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