NEUROANATOMY OF LANGUAGE 4 DAY 12 – SEPT 23, 2013 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University.

NEUROANATOMY OF LANGUAGE 4DAY 12 – SEPT 23, 2013

Brain & Language

LING 4110-4890-5110-7960

NSCI 4110-4891-6110

Harry Howard

Tulane University

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Course organization• The syllabus, these slides and my recordings are

available at http://www.tulane.edu/~howard/LING4110/.• If you want to learn more about EEG and neurolinguistics,

you are welcome to participate in my lab. This is also a good way to get started on an honor's thesis.

• The grades are posted to Blackboard.

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REVIEWThe quiz was the review

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EEG, ERP & MEG

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The basic fact about dipoles

A dipole has a direction … … which in cortex is perpendicular to its surface

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But, what do we know about the shape of the cortex?

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Inverse problems• Ideally, one would like to localize the precise neural sources that generate ERPs.

• This is an example of an “inverse problem”, because it tries to deduce the cause of an observation from the observation itself:• “An inverse problem is a general framework that is used to convert

observed measurements into information about a physical object or system that we are interested in.”

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How to calculate the source of a dipole

• How do we know which one is correct?• We can’t. There is no correct answer. • Dipole source localization is an ill-defined problem.

• That is to say, the inverse solution to the dipole source-localization problem is impossible to compute with certainty, because any given scalp distribution could, in principle, be generated by any number of source configurations within the brain.

+ -

+

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But …• … researchers have developed powerful tools that

provide good estimates of dipole localization, given some reasonable assumptions.

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LORETA

• One such method is known as LORETA (low resolution brain electromagnetic tomography), which provides an estimate of the current distribution throughout the entire 3-dimensional space within the brain.

• It does so by taking into account what is known about the structure of the brain and skull.

• An example of a LORETA solution, mapped onto a normalized brain space, is provided above.

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Comparison of EEG & MEG

EEG MEGSignal measured from electrical fields generated by

secondary (volume) currentsmagnetic fields generated by primary currents

Signal magnitude large (10 mV), easy to detect tiny (10 fT), difficult to detect

Dipole orientation sensitive to tangential and radial dipoles

sensitive only to tangential dipoles

Signal purity affected by skull, scalp, etc. unaffected by skull, scalp, etc.

Temporal resolution ~ 1 ms ~ 1 ms

Spatial resolution ~ 1 cm ~ 1 mm

Experimental flexibility allows some movement requires complete stillness

Cost cheap expensive

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MODELS OF NEUROLINGUISTIC FUNCTION

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Language areas of the brain

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The Broca-Wernicke-Lichtheim model (of the LH)

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The two main aphasiasIngram p. 49

Broca’s

• C: What brought you to the hospital?

• P: yes … ah … Monday … ah … Dad … Peter Hogan, and Dad … ah … hospital … and ah … Wednesday … Wednesday … nine o’clock and ah Thursday … ten o’clock … doctors two … two … an doctors and … ah … teeth … yah … and a doctor an girl … and gums, an I.

Wernicke’s

• C: What brings you to the hospital?

• Boy, I’m sweating, I’m awful nervous, you know, once in a while I get caught up, I can’t mention the tarripote, a month ago, quite a little, I’ve done a lot well, I impose a lot, while on the other hand, you know what I mean, I have to run around, look it over, trebbin and all that sort of stuff.

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NEXT TIMEIngram §4.

☞ Go over questions at end of chapter.

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