Neurolinguistics Sarah F. Phillips Language & Mind 13 November 2019 Lecture Roadmap • Foundations of Neurolinguistics • Lesion Analysis: Broca’s and Wernicke’s Area • The Classic Model • The Brain • Techniques used in Neurolinguistics • Hemodynamic techniques (PET, fMRI, fNIRS) • Electrophysiological techniques (EEG, MEG) • Integrating Theory, Methods, and Techniques • ELAN, N400, and P600 effects in EEG • Decomposing the N400 using MEG 1 Defining Neurolinguistics Neurolinguistics The scientific study of the neural bases of language Neurolinguistics Neurolinguistics Having to do with The scientific study the nervous system of language and its (the brain) structure 2 Foundations of Neurolinguistics: Broca’s Area • Pierre Paul Broca (1824-1880) • French physician and anatomist • Worked with patients who suffered from aphasias • In 1861, he first reported a link between a fluency aphasia and damage to a portion of the inferior frontal gyrus • This type of fluency aphasia is now known as “Broca’s Aphasia” • This region is often referred to as “Broca’s Area” Person with Broca’s Aphasia 4 Foundations of Neurolinguistics: Wernicke’s Area • Carl Wernicke (1848-1905) • German neurologist/neuropsychiatrist • Interested in linking behavioral abnormalities and brain lesions • In 1873, he studied a stroke patient who had difficulty with comprehension • This type of aphasia is now known as “Wernicke’s Aphasia” • His work studied to link this type of behavioral abnormality to a region now known as “Wernicke’s Area” 5 Person with Wernicke’s Aphasia 6 What have we learned so far? • Broca and Wernicke were interested in people with aphasia • Aphasia: any language disorder that results from brain damage caused by disease or trauma. • Broca’s Aphasia is characterized by slow, non-fluent speech • Wernicke’s Aphasia is characterized by fluent speech that is difficult to interpret/comprehend • Broca and Wernicke found that each of these types of aphasia were associated with damage to distinct regions of the brain 7 What have we learned so far? 8 Foundations of Neurolinguistics: Lesion Analysis as a method • These earlier ideas about the neural bases of language were largely built from lesion analysis • Broca and Wernicke studied the brains from people with aphasia port-mortem • The logic behind lesion analysis is that damage to a certain region must be what causes a particular problem in language production • Problem: There is no one-to-one correspondence between a lesion site and a symptom observed in language production • However, this early evidence argued for a modular organization of language in the brain 9 Foundations of Neurolinguistics: The Classic Model From Tremblay & Dick 2016, p. 62 (Fig.1) 10 Foundations of Neurolinguistics: Problems with the Classic Model • There is little consensus as to the location and size of Broca’s Area and Wernicke’s Area 11 Where is Broca’s Area? From Tremblay & Dick 2016, p. 65 (Fig.3) 12 Where is Wernicke’s Area? From Tremblay & Dick 2016, p. 64 (Fig.2) 13 Foundations of Neurolinguistics: Problems with the Classic Model • There is little consensus as to the location and size of Broca’s Area and Wernicke’s Area • Model is not spatially precise enough to make specific hypotheses about brain regions and their role in language behavior • Broca’s Area is involved with syntax? • Wernicke’s Area is involved with semantics? • What about phonology and morphology (or, the lexicon)? • Model ignores other cortical structures, subcortical structures, and white-matter pathways 14 Foundations of Neurolinguistics: The Brain • Cerebrum is the largest part of our brain, consisting of cortex and certain subcortical structures • Cerebellum is a part of the hind brain best known to be involved in motor control • Brainstem connects the cerebrum and cerebellum to the rest of the nervous system Image from https://mayfieldclinic.com/pe-anatbrain.htm 15 Foundations of Neurolinguistics: The Brain • Cerebrum consists of two hemispheres, the left and the right • The cortex is the outermost layer of the cerebrum • The cortex can be sectioned into four lobes in each hemisphere: frontal, temporal, parietal, and occipital • These areas of cortex are connected by white matter tracts • The two hemispheres are connected by the corpus callosum Image from https://mayfieldclinic.com/pe-anatbrain.htm 16 Techniques used in Neurolinguistics • Current technology allows us to study language in healthy brains in vivo, i.e. while people are still alive! • There are two main categories for the technology that is used: • Hemodynamic techniques • Electrophysiological techniques • Using these techniques, we present typical, healthy participants with language-based tasks and measure brain responses 17 Techniques used in Neurolinguistics: Hemodynamic • When a brain region becomes active, blood carrying oxygen rushes to that region • This Blood Oxygen Level-Dependent (BOLD) response is what’s measured by hemodynamic techniques • Positron-Emission Tomography (PET) 18 Positron Emission Tomography (PET) 19 Techniques used in Neurolinguistics: Hemodynamic • When a brain region becomes active, blood carrying oxygen rushes to that region • This Blood Oxygen Level-Dependent (BOLD) response is what’s measured by hemodynamic techniques • Positron-Emission Tomography (PET) • Functional Magnetic Resonance Imaging (fMRI) 20 Functional Magnetic Resonance Imaging (fMRI) Image from https://www.eurekalert.org/multimedia/pub/188089.php 21 Techniques used in Neurolinguistics: Hemodynamic • When a brain region becomes active, blood carrying oxygen rushes to that region • This Blood Oxygen Level-Dependent (BOLD) response is what’s measured by hemodynamic techniques • Positron-Emission Tomography (PET) • Functional Magnetic Resonance Imaging (fMRI) • Functional Near-Infrared Spectroscopy (fNIRS) 22 Functional Near-Infrared Spectroscopy (fNIRS) Image from https://www.cephalon.eu/products/navigation/brainsight-nirs/ 23 Techniques used in Neurolinguistics: Hemodynamic • When a brain region becomes active, blood carrying oxygen rushes to that region • This Blood Oxygen Level-Dependent (BOLD) response is what’s measured by hemodynamic techniques • Positron-Emission Tomography (PET) • Functional Magnetic Resonance Imaging (fMRI) • Functional Near-Infrared Spectroscopy (fNIRS) • Pro: High Spatial Resolution • Con: Poor Temporal Resolution 24 Techniques used in Neurolinguistics: Electrophysiological • When a neuron is sending information, an electrical signal passes through the axon • Electroencephalography (EEG) measures the flow of electric current produced by neurons Image from https://www.scienceabc.com/humans/electricity-generated-neurons-brain.html 25 Electroencephalography (EEG) Image from https://www.nhs.uk/conditions/electroencephalogram/ 26 Techniques used in Neurolinguistics: Electrophysiological • When a neuron is sending information, an electrical signal passes through the axon • Electroencephalography (EEG) measures the flow of electric current produced by neurons • Magnetoencephalography (MEG) measures the magnetic fields created by the electric current Image from https://www.scienceabc.com/humans/electricity-generated-neurons-brain.html 27 Magnetoencephalography (MEG) Image from NYU Abu Dhabi 28 Techniques used in Neurolinguistics: Electrophysiological • When a neuron is sending information, an electrical signal passes through the axon • Electroencephalography (EEG) measures the flow of electric current produced by neurons • Magnetoencephalography (MEG) measures the magnetic fields created by the electric current • Pro: High Temporal Resolution • Con: Low Spatial Resolution Image from https://www.scienceabc.com/humans/electricity-generated-neurons-brain.html 29 Integrating Theory, Methods, and Techniques • EEG recordings are chunked into epochs for analysis • EEG-measured brain activation that results from a stimulus are referred to as event related potentials (ERPs) • ERPs are labeled by activation polarity and latency • Activation polarity refers to whether the signal goes in a positive (P) or negative (N) direction • Latency refers to how long (typically in milliseconds) it takes for the peak to occur after the onset of the stimulus 30 Friederici’s (1995) Model of Language Processing • Evidence from ERPs suggests (at least) three stages of language processing: • ELAN à Word Categorization • LAN/N400 à Semantic Integration • P600 à Syntactic reanalysis 31 Early Left Anterior Negativity (ELAN) 32 Left Anterior Negativity (LAN)/ N400 From Kutas & Hillyard (1980) 33 P600 From Osterhout et al. 1994, p. 790 (Fig. 2) 34 Integrating Theory, Methods, and Techniques • MEG recordings are chunked into epochs for analysis • MEG-measured brain activation that results from a stimulus are referred to as event related fields (ERFs) • Spatial resolution is better than EEG (but not as good as any hemodynamic technique) 35 Decomposing the N400 with MEG From Pylkkänen & Marantz 2003, p. 188 (Fig. 1) 36 In Summary… • Based on foundational work by Broca and Wernicke, we have conceptualized a modular organization of the brain • Current neurolinguistic research uses hemodynamic and electrophysiological techniques • Hemodynamic techniques (e.g. fMRI) give better spatial resolution • Electrophysiological techniques (e.g. EEG, MEG) give better temporal resolution • Classical findings in the electrophysiological literature (ELAN, N400, P600) give us the basic neural correlates of language processing 37 Bonus! What about bilinguals? From Bemis & Pylkkänen 2011 38 Bonus! What about bilinguals? 39 Bonus! What about bilinguals? 40.