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Neurophysiology of Communication Neurophysiology of Communication Presented by: Neha Sharma MD Date: October 11, 2019 What is Communication? Ø The imparting or exchange of information Ø Auditory, Language, Speech, and Comprehension Ø Focus of presentation – how language and speech are perceived and comprehended by the brain Neurophysiology of Hearing Neurophysiology of Hearing Ø Frequency of sound as speech (sound waves) Ø Frequency of speech is 60-500 Hz Ø Males – 85-180 Hz; Female – 165-255 Hz Ø Ear picks up 20-20,000 Hz Animal Frequencies Animal Vocal Frequency (Hearing Frequency) Elephants 14-24 Hz (14-12,000 Hz) Dogs 1,000-2,000 Hz (67-45,000 Hz) Birds 1,000-8,000 Hz (200-8,500 Hz) Ants 1,000 Hz (500-1500 Hz) Mice/Rats 20,000-100,000 Hz (1,000-100,000 Hz) Cow 70-7,000 Hz (16-40,000 Hz) Bats 50,000-160,000 Hz (2,000-110,000 Hz) Torrent Frog 128,000 Hz (38,000 Hz) Katydid 138,000 Hz-150,000 Hz (15,000-50,000 Hz) Dolphins 175,000 Hz (75-150,000 Hz) Wax Moth 300,000 Hz (300,000 Hz) Auditory Anatomy https://endoplasmiccurriculum.wordpress.com/2012/03/09/internal-ear-anatomy/ Neurophysiology of Hearing Ø Sound waves transmit through the air to the ear Ø Travels through external acoustic meatus to auditory canal to tympanic membrane Ø Oscillate against the ossicles which causes vibration of the oval window Ø Stimulating the cochlea which converts the vibration into electrical signals Ø Hair cells move upwards and forwards causing depolarization of the basilar membrane Ø Due to perturbation of basilar membrane against tectorial membrane Ø Inner hair cells – discriminate frequency Ø Outer hair cells – sound amplification Neurophysiology of Hearing Ø Base of hair cell releases Glutamate after depolarization Ø Stimulates the Vestibulocochlear nerve (Cranial Nerve VIII (CN VIII)) via spiral ganglion of modiolus https://www.studocu.com/en/document/indiana-university/cell-biology-histology/summaries/histology-of-the-ear-notes/1366464/view Auditory Pathway Ø Cochlear nucleus Ø Dorsal cochlear nucleus and Posteroventral cochlear nucleus Ø Sound identification Ø Anteroventral cochlear nucleus Ø Sound localization Ø Efferent to medial superior olive Ø Signal ascends up to inferior colliculus then to medial geniculate body Ø Finally to primary auditory cortex http://www.humanneurophysiology.com/soundhearing.htm Localization of Sound Ø Localization of sound ØLateral sound source stimulates contralateral lemniscus fibers of medial superior olivary nucleus to inferior colliculus Ø Weber test Ø Tuning fork on head – should hear it equally bilaterally Ø Affected ear louder – conductive Ø Unaffected ear louder – sensorineural Ø Rinne test http://www.humanneurophysiology.com/soundhearing.htm Ø Tuning fork on mastoid process – then anterior to acoustic meatus Ø AC>BC – normal Ø BC>AC – conductive hearing loss Neurophysiology of Language and Speech Language Ø Form Ø Syntax – guidelines for combining words into sentences Ø Phonology – guidelines for combining sounds into a pattern of language (laryngeal muscles) Ø Content and use Ø Grammar – guidelines for usage of vocabulary to be combined into sentences Ø Language and speech develop mostly by age 5 Neurophysiology of Language and Speech https://www.researchgate.net/figure/Language-specific-areas-in-the-brain_fig1_317356553 Components of Comprehension Components of Comprehension Ø Frontal lobe Ø Inferior frontal gyrus – Broca's area – planning and production of speech articulation Ø BA 44,45,47 Ø Parietal lobe Ø Angular gyrus – written comprehension (BA 39) Ø Supramarginal gyrus – phonological processing (BA 6) Ø Temporal lobe Ø Wernicke's area – language comprehension Ø Superior temporal sulcus – language comprehension Ø Heschl's gyrus – auditory reception https://www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(14)00170-3 Ø Belt – auditory signal differentiation Ø Parabelt – auditory information processing Ø Corpus callosum – connect both cerebral hemispheres Ø Plays role in language lateralization Components of Comprehension Ø Midbrain Ø Medial geniculate nucleus – auditory relay (part of Thalamus) Ø Inferior colliculus – auditory relay (localizes sound) Ø Thalamus Ø Pulvinar – language relay Ø Medial geniculate nucleus – auditory relay Ø Ventral (BA 41), dorsal (BA 42 and belt) Ø Belt and parabelt project to temporal, parietal and frontal lobes for processing Components of Comprehension Ø Basal ganglia Ø Executive functions, speech motor control, learning Ø Superior olivary nucleus Ø Lateral superior olive Ø Sound intensity and determines location in horizontal space Ø Medial superior olive Ø Frequency for timing of sound and determines location in horizontal space Ø Olivocochlear bundle Ø Efferent auditory pathway, from superior olivary complex to cochlea, allows for discrimination of noise (focus on signal) Components of Comprehension Ø Insular cortex (dominant hemisphere) Ø Speech praxis Ø Pons Ø Cochlear nuclei – first relay to brainstem for auditory Ø Superior olivary complex – auditory localization Ø Periolivary nuclei – efferent auditory system Ø Lateral lemniscus – cochlear nucleus to inferior colliculus auditory tract Ø Striae of Held and Monaco – dorsal nucleus bilateral input; ventral nucleus contralateral input Components of Comprehension Ø Cerebellum Ø Cerebro-cerebellar pathways Ø Corticopontine-cerebellar and cerebellar-thalamic-cortical loops Ø Connect cerebellum with motor, paralimbic and association cortices sub serving cognitive and affective processes Ø Speech timing, pitch discrimination and verbal fluency Ø Cerebellum is part of a sub-cortical pathway Ø Input from Broca's area (BA 44) via the left anterior insula and projects to left primary motor cortex (M 1) via the (left) ventral premotor cortex (PMC) Left side: thought and motor aspect of speech; Right side: auditory comprehension Seikel, J., Konstantopoulos, K., & Drumright, D. (2019). Neuroanatomy and neurophysiology for speech and hearing sciences. Thoughts, Speech, Interpretation Neural Control of Speech Ø Linguistic system in lateral frontal lobe of the dominant hemisphere Ø Grammar in Broca's area, phonetic encoding in left insular cortex and left supramarginal gyrus Ø Motor loops for speech Ø Preparative loop – left dorsolateral prefrontal cortex, anterior insular cortex, supplementary motor area and superior cerebellum Ø Executive loop – motor cortex, thalamus, putamen, caudate, inferior cerebellum Ø Basal ganglia support initiation of speech production and phonological processing Thoughts, Speech, Interpretation Ø Producer of speech Ø Starts as a concept (thought) – formulated into a sound (temporoparietal junction and cerebellum) – articulation (motor movement at Broca's) Ø Supramarginal gyrus and primary sensory cortex (BA 1) interpret articulation and if correction is needed information is sent to cerebellum and premotor cortex Ø Listener of speech Ø Internalization of words then are interpreted to match already learned language Ø Lemma – mental representation reflecting the stage between activating an idea and activating speech to express the idea Ø Use of definitions and syntax for interpretation Bilingualism What is Bilingualism? Ø Bilingual – fluency in two languages Ø One language is dominant, other language is secondary Ø Ability to move from one language to the other Ø Word association model – words can be interchanged from L1 to L2 and vice versa https://www.cambridge.org/core/books/teaching-chinese-as-an-international-language/use-of-english-in-the-teaching-of-chinese-making-the-most-of-the-learners-linguistic-resources/AEAE802107F0737E36E52DBEE8057EF4 Ø Concept mediation hypothesis – L1 needs to refer to concept and with L2 Green's Inhibitory Control Model – how to switch from L1 to L2 to complete a task after goal has been established https://www.researchgate.net/figure/Greens-Inhibitory-Control-Model_fig4_259800186 Bilingual "Code-Switching" Ø Bilingual people can "Code-switch" Ø Switching between language one and language two Ø Common in immigrant families Ø People switch between languages in one conversation or even sentence Ø Hypothesis Ø Left caudate has been shown to be primary site of language switching Ø Damage to left caudate causes person to involuntary switch Bilingual "Code-Switching" Ø Equivalence Constraint Ø Codes are switched when surface structure of language maps overlap Ø Free Morpheme Constraint Ø Codes are switched whenever possible/desired Ø L1-L2 share similar language areas but are not identical Ø Proficiency determines neural composition Bilingual "Code-Switching" Ø Conflicts in grammar and syntax between languages occur and processes need to be inhibited appropriately Ø Basal ganglia, thalamus, anterior cingulate cortex, and frontal lobe control inhibition of language Ø Inhibition is not all or none – hence allowing for sentential switching Ø Abutalebi and Green model features five brain regions at work: left DLPFC, ACC, caudate nucleus, and bilateral SMG Ø Luk et al. model supports the role of left PFC and caudate, doesn't include the ACC and bilateral SMG. Additionally, activations are seen in the pre-SMA, the right precentral gyrus, and the left middle temporal gyrus Bilingual "Code- Figure 1 Switching" L1 and L2 Mixed against control condition showed increased activity in a network of areas including the left IFG, the precentral gyrus, SMA, the left IPG, the bilateral fusiform gyrus extending to the occipital lobe, as well as the subcortical regions including the left caudate, and the right hippocampus Bilingual "Code- Figure 2 Switching" L1 Chinese naming condition showed broadly
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