Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
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
EEG ECG
Electro-Encephalograghy (EEG)
• Electrical current originating in the cortical areas • Measured across scull and tissue - adjustments
for physical properties
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
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. 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