Cortex Sept 22, 2017 – DAY 11 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Course organization http://www.tulane.edu/~h0Ward/BrLg/ Fun with https://www.facebook.com/BrLg17/ I am still working on grading.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Review

Axons vs. apical dendrites (in cortex) 22-sep-2017 Brain & Language - Harry Howard - Tulane University Axons vs. apical dendrites (in cortex) 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.

Tonotopy in the ascending auditory pathway 22-sep-2017 Brain & Language - Harry Howard - Tulane University Tonotopy in the ascending auditory pathway Hayhoe07-CentralAuditoryPath.pdf

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Winer05-CentralAudPathway.pdf

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Experimental animals

Brain stem frequency-following response 22-sep-2017 Brain & Language - Harry Howard - Tulane University Brain stem frequency-following response The human brain stem frequency-following response (FFR) registers phase-locked neural activity to cyclical auditory stimuli. Galbraith et al., (1995) We show that the FFR can be elicited by word stimuli, and when speech-evoked FFTs are reproduced as auditory stimuli they are heard as intelligible speech Galbraith, Gary C., Paul W. Arbagey et al. “Intelligible Speech Encoded in the Human Brain Stem Frequency-Following Response.” NeuroReport 6.17 (1995)

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Timing, pitch, and timbre in the stimulus (black) and brain stem response (gray) waveforms Kraus, Nina, Erika Skoe et al. “Experience-Induced Malleability in Neural Encoding of Pitch, Timbre, and Timing.” Annals of the New York Academy of Sciences 1169.1 (2009): 543-57.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University subcortical Audition

Can experience have any effect? 22-sep-2017 Brain & Language - Harry Howard - Tulane University Can experience have any effect? Grand average brain stem responses to the speech syllable “da” for both musician (red) and non-musician (black) groups in the audiovisual condition. Top: Amplitude differences between the groups are evident over the entire response waveform. Middle: Musicians exhibit faster (i.e., earlier) onset responses. Bottom. Fourier analysis shows musicians to have more robust amplitudes of the F0 peak (100 Hz) and the peaks corresponding to the harmonics (200, 300, 400, 500 Hz) (left). Kraus, Nina, Erika Skoe et al. “Experience-Induced Malleability in Neural Encoding of Pitch, Timbre, and Timing.” Annals of the New York Academy of Sciences 1169.1 (2009): 543-57.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Pitch tracking The thin black line represents the pitch contour of the stimulus (Mandarin tone 3), and the thick gray line represents the extracted pitch trajectory of the brain stem response. The musician's brain response follows the pitch of the stimulus more precisely, a phenomenon known as pitch tracking. Kraus, Nina, Erika Skoe et al. “Experience-Induced Malleability in Neural Encoding of Pitch, Timbre, and Timing.” Annals of the New York Academy of Sciences 1169.1 (2009): 543-57.

One hour of phonetic discrimination training vs passive listening 22-sep-2017 Brain & Language - Harry Howard - Tulane University One hour of phonetic discrimination training vs passive listening Grand-average FFR power spectra (i.e., subtracted polarities) at T0 (pre, red line) and T1 (post, blue line) of the trained group (upper part) and passive-listening (lower part). f0 = fundamental frequency, f1–f6 = harmonics. Elmer, Stefan, Marcela Hausheer et al. “Human Brainstem Exhibits Higher Sensitivity and Specificity Than Auditory-Related Cortex to Short-Term Phonetic Discrimination Learning.” Scientific Reports 7 (2017): 7455.

The descending pathway 22-sep-2017 Brain & Language - Harry Howard - Tulane University The descending pathway thalamus McLachlan10 midbrain

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Some conclusions Cortex is generally held to be the seat of learning ~ neural plasticity. The fact that subcortical nuclei can alter their response -- presumably under the direction of auditory cortex -- shows that Realism stops there and Constructivism takes over. We still don't know where auditory objects are constructed, though.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University cortex

Vertical organization: lamination 22-sep-2017 Brain & Language - Harry Howard - Tulane University Vertical organization: lamination

Functional Histology of the Cerebral Cortex Neocortex has 6 layers designated I, II, III, IV, V, VI Pyramidal cells predominate in layers III and V Granule cells in layers II and IV neuro_chap15.ppt 22-sep-2017 Brain & Language - Harry Howard - Tulane University

Brain & Language - Harry Howard - Tulane University Types of Cortex Cytoarchitecture varies in different areas Number and size of cells Thickness of layers neuro_chap15.ppt 22-sep-2017 Brain & Language - Harry Howard - Tulane University

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Brodmann's areas

Brodmann's areas, functions 22-sep-2017 Brain & Language - Harry Howard - Tulane University Brodmann's areas, functions

Horizontal organization: minicolumn 22-sep-2017 Brain & Language - Harry Howard - Tulane University Horizontal organization: minicolumn

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University EEG & MEG

Brain & Language - Harry Howard - Tulane University 22-sep-2017 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. http://en.wikipedia.org/wiki/Electroencephalography http://74.124.210.21/research-division-research-products/sensor-nets

Magnetoencephalography (MEG) 22-sep-2017 Brain & Language - Harry Howard - Tulane University Magnetoencephalography (MEG) … records magnetic fields produced by using arrays of SQUIDs (superconducting quantum interference devices). http://en.wikipedia.org/wiki/Magnetoencephalography

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University An EEG http://en.wikipedia.org/wiki/Electroencephalography http://en.wikipedia.org/wiki/Image:Spike-waves.png

Electrical-chemical-electrical communication at the synapse 22-sep-2017 Brain & Language - Harry Howard - Tulane University Electrical-chemical-electrical communication at the synapse http://txtwriter.com/Backgrounders/Drugaddiction/synapse.jpg

Pre- and post-synaptic currents 22-sep-2017 Brain & Language - Harry Howard - Tulane University Pre- and post-synaptic currents

22-sep-2017 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. Magnetic fields are also created by volume currents, but approximately cancel and sum to zero. Assuming a spherical head, they would precisely sum to zero.

Currents, fields and a dipole 22-sep-2017 Brain & Language - Harry Howard - Tulane University Currents, fields and a dipole Kahkonen-Fig_1a.gif

Another take on currents and fields 22-sep-2017 Brain & Language - Harry Howard - Tulane University Another take on currents and fields

Axons vs. apical dendrites 22-sep-2017 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.

The basic fact about dipoles 22-sep-2017 Brain & Language - Harry Howard - Tulane University The basic fact about dipoles A dipole has a direction … … which in cortex is perpendicular to its surface http://en.wikipedia.org/wiki/File:VFPt_dipole_electric.svg

But, what do we know about the shape of the cortex? 22-sep-2017 Brain & Language - Harry Howard - Tulane University But, what do we know about the shape of the cortex? http://www.mrc-cbu.cam.ac.uk/research/eeg/eeg_intro.html

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Another dipole

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University 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.” http://faculty.washington.edu/losterho/erp_tutorial.htm http://en.wikipedia.org/wiki/Inverse_problem

How to calculate the source of a dipole 22-sep-2017 Brain & Language - Harry Howard - Tulane University 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.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University But … … researchers have developed powerful tools that provide good estimates of dipole localization, given some reasonable assumptions.

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University 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. http://faculty.washington.edu/losterho/erp_tutorial.htm http://faculty.washington.edu/losterho/images/loreta1.jpg

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University Comparison of EEG & MEG EEG MEG Signal measured from electrical fields generated by secondary (volume) currents magnetic 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 Spatial resolution ~ 1 cm ~ 1 mm Experimental flexibility allows some movement requires complete stillness Cost cheap expensive

Brain & Language - Harry Howard - Tulane University 22-sep-2017 Brain & Language - Harry Howard - Tulane University NEXT TIME P3 Auditory cortex