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 fMRI SPECT X-ray PET CT/CAT EEG ECG

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

EEG Strengths: Weaknesses 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 P3 N400 P600 P2 N2

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

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

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

+ - current

MEG Strengths Weaknesses High temporal resolution 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