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Neuroanatomy of language 3 Sept 20, 2013 – DAY 11

Neuroanatomy of language 3 Sept 20, 2013 – DAY 11. Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University. Course organization. The syllabus, these slides and my recordings are available at http://www.tulane.edu/~howard/LING4110/ .

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Neuroanatomy of language 3 Sept 20, 2013 – DAY 11

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  1. Neuroanatomy of language 3Sept 20, 2013 – DAY 11 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University

  2. Brain & Language - Harry Howard - Tulane University 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.

  3. Brain & Language - Harry Howard - Tulane University Review Macrostructure

  4. Brain & Language - Harry Howard - Tulane University Macrostructure review • Three axes of the brain • Vertical = dorsal - ventral • Horizontal • Longitudinal = anterior - posterior • Lateral = lateral - medial • Connections • corpus callosum, arcuate fasciculus • Naming conventions • Gyrii ~ sulcii • Brodmann's areas • Stereotaxic (“Talairach”) coordinates

  5. Brain & Language - Harry Howard - Tulane University EEG, ERP & MEG

  6. Brain & Language - Harry Howard - Tulane University Basic ideas • The electrical activity of neurons produces currents spreading through the head. • These currents reach the surface of the scalp in the form of voltage changes and magnetic fields, both of which can be measured non-invasively. • Voltage changes measured at the scalp are called an electroencephologram(EEG). • Magnetic fields measured at the scalp are called an magnetoencephologram(MEG).

  7. Brain & Language - Harry Howard - Tulane University Electrical activity of neurons • Each neuron consists of a cell body, short threadlike projections called dendrites, and one longer thread called an axon. • Impulses travel within a neuron in the form of electrical signals, but between them as chemical signals. • The electrical signal is changed to a chemical one at the synapse, and then changed back to an electrical one on the other side of the synapse. post-synaptic, dendrites pre-synaptic, axon

  8. Brain & Language - Harry Howard - Tulane University Electrical-chemical-electrical communication at the synapse

  9. Brain & Language - Harry Howard - Tulane University Pre- and post-synaptic currents

  10. Brain & Language - Harry Howard - Tulane University Layout of dendrites of pyramidal cells apical dendrites basal dendrites

  11. Brain & Language - Harry Howard - Tulane University Axons vs. apical dendrites • Axons are oriented randomly along the cortical sheet, which results in their potentials cancelling one other out. • Apical dendrites are oriented in parallel along the cortical sheet, which results in their potentials to reinforce one another and sum together, creating a large “dipole”, which is measurable with EEG/MEG.

  12. Brain & Language - Harry Howard - Tulane University Currents and fields • Primary or intracellular current (what we want to know about) does not summate across axons. • Summation of parallel dendrites in cortical sheet creates: • Secondary or extracellular or volume currents • Magnetic field perpendicular to primary current The paired positive and negative ‘ends’ of the volume current are known as a dipole.

  13. Brain & Language - Harry Howard - Tulane University Another take on currents and fields

  14. Brain & Language - Harry Howard - Tulane University Currents, fields and a dipole

  15. Brain & Language - Harry Howard - Tulane University Another dipole

  16. Brain & Language - Harry Howard - Tulane University The basic fact about dipoles A dipole has a direction … … which in cortex is perpendicular to its surface

  17. Brain & Language - Harry Howard - Tulane University But, what do we know about the shape of the cortex?

  18. Brain & Language - Harry Howard - Tulane University Summary • The electrical activity of neurons produces currents that spread through the head. • These currents reach the surface of the scalp in the form of voltage changes and magnetic fields, both of which can be measured non-invasively. • Voltage changes measured at the scalp are called an electroencephologram(EEG). • Magnetic fields measured at the scalp are called an magnetoencephologram(MEG).

  19. Brain & Language - Harry Howard - Tulane University Scalp EEG • Scalp EEG is collected from tens to hundreds of electrodes positioned on different locations at the surface of the head. • EEG signals (in the range of millivolts) are amplified and digitalized for later processing.

  20. Brain & Language - Harry Howard - Tulane University Magnetoencephalography (MEG) • … records magnetic fields produced by using arrays of SQUIDs (superconducting quantum interference devices).

  21. Brain & Language - Harry Howard - Tulane University Comparison of EEG & MEG

  22. Brain & Language - Harry Howard - Tulane University An EEG

  23. Brain & Language - Harry Howard - Tulane University ERP • Event-related brain potentials (ERPs) are positive and negative voltage fluctuations (or components) in the EEG that are time-locked to the onset of a sensory, motor, or cognitive event. • ERPs reflect brain activity that is specifically related to some event, usually the onset of a stimulus. • This activity cannot be directly observed in the EEG: • the EEG is a composite of simultaneously occurring brain activity, • so it doesn't reflect just the activity associated with the event of interest. • In other words, the "signal" (the brain response to some event) is swamped by the "noise" (the brain activity that is unrelated to that event).

  24. Brain & Language - Harry Howard - Tulane University Signal averaging • The solution to this problem is to present not just one instance of the event, but many instances. • Epochs of brain activity, each one time-locked to the onset of the event, are then averaged together. • The "random" activity washes out during averaging, whereas the brain activity of interest - namely, what is constant over presentations of the event - stays in the signal. • Through this signal-averaging procedure, it is possible to isolate the brain response that is specifically elicited in response to some event of interest.

  25. Brain & Language - Harry Howard - Tulane University ERP procedure and componentsnamed by their polarity and peak latency (in ms)

  26. Brain & Language - Harry Howard - Tulane University NEXT TIME P3 Any leftovers from Ingram §3; go on to §4. ☞ Go over questions at end of chapter.

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