NEUROANATOMY OF LANGUAGE 4 DAY 12 – SEPT 23, 2013 Brain & Language LING NSCI Harry Howard Tulane University

Course organization The syllabus, these slides and my recordings are available at 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. 9/23/13Brain & Language - Harry Howard - Tulane University 2

REVIEW The quiz was the review 9/23/13Brain & Language - Harry Howard - Tulane University 3

EEG, ERP & MEG 9/23/13Brain & Language - Harry Howard - Tulane University 4

The basic fact about dipoles A dipole has a direction … … which in cortex is perpendicular to its surface 9/23/13Brain & Language - Harry Howard - Tulane University 5

But, what do we know about the shape of the cortex? 9/23/13Brain & Language - Harry Howard - Tulane University 6

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.” 9/23/13Brain & Language - Harry Howard - Tulane University 7

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 /23/13Brain & Language - Harry Howard - Tulane University 8

But … … researchers have developed powerful tools that provide good estimates of dipole localization, given some reasonable assumptions. 9/23/13Brain & Language - Harry Howard - Tulane University 9

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. 9/23/13Brain & Language - Harry Howard - Tulane University 10

Comparison of EEG & MEG EEGMEG Signal measured from electrical fields generated by secondary (volume) currents magnetic fields generated by primary currents Signal magnitudelarge (10 mV), easy to detecttiny (10 fT), difficult to detect Dipole orientation sensitive to tangential and radial dipoles sensitive only to tangential dipoles Signal purityaffected by skull, scalp, etc.unaffected by skull, scalp, etc. Temporal resolution~ 1 ms Spatial resolution~ 1 cm~ 1 mm Experimental flexibilityallows some movementrequires complete stillness Costcheapexpensive 9/23/13Brain & Language - Harry Howard - Tulane University 11

MODELS OF NEUROLINGUISTIC FUNCTION 9/23/13Brain & Language - Harry Howard - Tulane University 12

9/23/13Brain & Language - Harry Howard - Tulane University 13 Language areas of the brain

9/23/13Brain & Language - Harry Howard - Tulane University 14 The Broca-Wernicke-Lichtheim model (of the LH)

The two main aphasias Ingram 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. 9/23/13Brain & Language - Harry Howard - Tulane University 15

NEXT TIME Ingram §4. ☞ Go over questions at end of chapter. 9/23/13Brain & Language - Harry Howard - Tulane University 16