Lecture 4 - Hearing - PSYC112/132 - Lancaster University - Nov 2024 PDF

11/11/2024 PSYC112/132: Introduction to Neuroscience Whilst we wait to get started… Week 7: Wednesday 20th November 2024 Dr Abigail Fiske [email protected] 1 Quest...

11/11/2024 PSYC112/132: Introduction to Neuroscience Whilst we wait to get started… Week 7: Wednesday 20th November 2024 Dr Abigail Fiske [email protected] 1 Questions, Comments, Concerns? Please do get in touch – I’m very happy to help [email protected] Office: Fylde C42 Book a meeting with me here Message me on Microsoft Teams Post in the Discussion Forum 2  11/11/2024 Module Part 2: Sensory and Motor Systems 3 Lecture 3: Hearing 4  11/11/2024 Learning Objectives Describe the anatomy of the auditory system Understand how the auditory system converts sound into electrochemical signals in the brain In brief: understand the role of the vestibular system and how damage to the auditory system can result in deafness By the end of the lecture, you will have a basic understanding of the auditory system and the process by which the brain can “hear” sounds. 5 The “Why” Hearing is crucial for communication and interaction with the environment Links between sensory processing and how the brain interprets external sound stimuli Understanding the auditory system lays the groundwork for exploring communication disorders, sensory deficits, deafness (clinical) and hearing research in Psychology 6  11/11/2024 Part I: Sensory Systems 7 Sensory Areas of the Cortex Sensory cortex = brain areas that process sensory input Five main sensory cortices: Auditory (hearing) = temporal lobe Visual (seeing) = occipital lobe Gustatory (tasting) = insular / frontal lobe Olfactory (smelling) = temporal lobe Somatosensory (touch, pressure, temperature, pain) = post central gyrus 8  11/11/2024 Sensory Areas of the Cortex For each sensory area… Primary sensory cortex – receives most of its input directly from the thalamus Secondary sensory cortex – receive most of its information from the primary sensory cortex of from other areas of secondary sensory cortex Association cortex – any area of the cortex that receives input from more than one sensory system 9 Sensory System Organisation Hierarchical: Each level receives its input from lower layers and adds another layer of analysis before passing up the hierarchy Parallel: Information flows through parallel Functional Segregation: components over Each level contains multiple pathways functionally distinct and is analysed areas that specialise in simultaneously in different kinds of 10 each pathway analysis  11/11/2024 Part II: The Nature of Sound 11 The McGurk Effect – Sensory Integration 12  11/11/2024 Auditory System Function of the auditory system is the perception of sound Sound = vibrations of air molecules that stimulate the auditory system Sound travels relatively slowly (~330ms) Auditory system = more than just the outer ear! 13 Dimensions of Sound Sounds are recorded in the forms of waves dB Physical dimension (amplitude, frequency, complexity) Perceptual dimensions (loudness, Hz pitch, timbre) Pure tone (sine wave vibration) is the building block of sound – but don’t exist in the real world! 14  11/11/2024 Amplitude: How loud is loud? 15 Frequency: The “shape” of sound (pitch) Sound waves have different frequencies Frequency range of audible sound (for humans) is 20 Hz – 20,000 Hz Human hearing frequency changes with age Human hearing loss below 8,000 Hz affects everyday perception 16  11/11/2024 Frequency The higher the frequency of vibration, the higher the frequency of the sound waves Change in frequency Same amplitude 17 Timbre Most sounds are “complex” – a Pure tones combination of multiple frequencies Any complex sound wave can be produced by adding together sinusoidal sound waves (pure tones) The amplitudes and frequencies of these components determine the spectrum of the sound 18  11/11/2024 Spectrum of Sound Pressure = propagation (spreading) of sound through air A plot of the simple wave components of a complex sound wave Frequency (x-axis) – number of times a wave repeats itself in one second - Hz Amplitude (y-axis) intensity of a wave (perceived as loudness) - dB 19 Spectrogram Try it yourself! https://musiclab.chromeexperiments.com/Spectrogram/ 20  11/11/2024 Part II: Auditory System 21 Overview of the Auditory System Peripheral auditory system – outer, middle and inner ear where sound is received and converted to electrical signals Central auditory system – transports electrical auditory signals from the cochlea to the brain where they are processed 22  11/11/2024 Peripheral Auditory System – Outer Ear Sound is directed into the ear canal by the pinna Travels through the ear canal to the tympanic membrane (ear drum) Functions of the outer ears include: Filtering sound according to frequency Amplifying auditory signals Providing information about the direction of sound (based on timing of which sound reaches the ear first) Outer Ear 23 Graham, A. S., Ben-Azu, B., Tremblay, M. È., Torre III, P., Senekal, M., Laughton, B.,... & Holmes, M. J. (2023). A review of the auditory-gut-brain axis. Frontiers in Neuroscience, 17, 1183694. Peripheral Auditory System – Middle Ear Middle ear helps to amplify sound Spans from the tympanic membrane (ear drum) to the oval window of the cochlea Three important bones involved in the transmission of sound through the middle ear: Malleus (“hammer”) Incus (“anvil”) Stapes (“stirrup”) Sound is transmitted through the middle ear as a mechanical signal (vibrations) Vibrations reach the three middle ear bones Connects ear with – which cause the oval window to vibrate nose and respiratory system 24 Graham, A. S., Ben-Azu, B., Tremblay, M. È., Torre III, P., Senekal, M., Laughton, B.,... & Holmes, M. J. (2023). A review of the auditory-gut-brain axis. Frontiers in Neuroscience, 17, 1183694.  11/11/2024 Peripheral Auditory System – Inner Ear Mechanical signals are converted to electrical signals in the inner ear As the stapes vibrates, this causes the membrane of the oval window to vibrate This transfers vibrations to the fluid of the cochlea Cochlea is a long, coiled tube with an internal structure running to its tip (organ of Corti) 25 Graham, A. S., Ben-Azu, B., Tremblay, M. È., Torre III, P., Senekal, M., Laughton, B.,... & Holmes, M. J. (2023). A review of the auditory-gut-brain axis. Frontiers in Neuroscience, 17, 1183694. Peripheral Auditory System – Inner Ear: Organ of Corti Organ of Corti consists of several membranes, including: Basilar membrane Tectorial membrane Auditory receptors (hair cells - stereocilia) are mounted in the basilar membrane, and they touch the tectorial membrane Vibrations reaching these receptors cause the hair cells to move, which increases firing in axons of the auditory nerve (translates sound from mechanical to electrical signal) 26 Graham, A. S., Ben-Azu, B., Tremblay, M. È., Torre III, P., Senekal, M., Laughton, B.,... & Holmes, M. J. (2023). A review of the auditory-gut-brain axis. Frontiers in Neuroscience, 17, 1183694.  11/11/2024 Basilar Membrane Basilar membrane (runs the length of the cochlea) is “tuned” so that each place on the membrane responds to a particular frequency of sound Base = high frequency Apex = low frequency This helps to separate out different frequency components of a complex sound 27 Place Coding of Sound Frequency Different frequencies of sound produce activity at different places on the basilar membrane Auditory nerve fibres connect to each place, hence different nerve fibres are sensitive to different frequencies This place coding of frequency (neurons in different places in an array responding to different frequencies) continues up to auditory cortex This spectral information is used by the brain to identify sounds, and to separate out sounds that occur together 28  11/11/2024 29 A brief detour: The Vestibular System A sensory system essential to normal movement and balance Provides information about motion, head position, spatial orientation, balance, posture, stability of head and body during movement Inner ear  vestibular labyrinth (semicircular canals) connected to the cochlea Fluid-filled – when head is moved, fluid moves, causes hair cell movement, generates an action potential 30  11/11/2024 Part III: Transduction and Neural Processing 31 The Inner Ear – Hair Cells Sensory hair cells (auditory receptors) are organised along Inner Hair Cells the basilar membrane Inner hair cells (3,500 per ear) are organised in one row – necessary for auditory transduction Outer hair cells (12,000 per ear) Outer Hair Cells are organised in three rows - act like a frequency tuner Inner hair cells possess stereocilia which are connected to the tectorial membrane 32  11/11/2024 Transduction As the basilar membrane vibrates up and down, the Stereocilia stereocilia (hair cells) are bent from side to side Inner Hair Outer Hair Basilar Cell Cells Membrane 33 34  11/11/2024 Transduction Stereocilia press against the tectorial membrane Tip links are extracellular filaments that connect the stereocilia to each other in the inner ear Tip links connect to ion channels in the cell membrane causing them to open An influx of positively charged potassium ions (K+) enters the cell, causing it to depolarise 35 Transduction The inner hair cells depolarise and release a neurotransmitter – this triggers the process of neural transmission BUT only when stereocilia are bent in one direction (phase locking – synchronised to the vibration) Louder sound = more energy = more vibration = greater movement of hair cells on basilar membrane = more K+ enters stereocilia = more NT release = higher firing rate = more neural activation in auditory nerve 36  11/11/2024 Central Auditory System Auditory nerve is the start of the central auditory system and is where the auditory system and brain meet Carries electrical signals from cochlea to the brainstem Brainstem  superior olivary complex  inferior colliculus  medial geniculate body  auditory cortex White matter tracts connect structures of the central auditory system Damage to peripheral auditory system can have problematic effects in the central auditory system 37 Graham, A. S., Ben-Azu, B., Tremblay, M. È., Torre III, P., Senekal, M., Laughton, B.,... & Holmes, M. J. (2023). A review of the auditory-gut-brain axis. Frontiers in Neuroscience, 17, 1183694. Major integrative centre; pitch may be extracted here Relatively little is understood Binaural - Inputs from about the auditory cortex two ears combined here; sound location 38 determined  11/11/2024 Part IV: Damage to the Auditory System 39 Effects of Damage to the Auditory System Studying damage to the auditory system can tell us more about how the auditory system works and can provide information about the causes and treatment of deafness Deafness is one of the most common human disabilities (~360 million people) Total deafness is rare (~1% of hearing- impaired individuals) 40  11/11/2024 Deafness and hearing impairments Hearing loss can be associated with tinnitus (ringing of the ears) Damage to the ossicles = conductive deafness Damage to the cochlea or auditory nerve = nerve deafness Major cause of nerve deafness is a loss of hair cell receptors If only part of cochlea damaged, people may have deafness only at some frequencies Some people may benefit from cochlear implants 41 HOMEWORK 1. READ CHAPTER 7 OF THE TEXTBOOK (the part on hearing) 2. Check out the short YouTube videos on this topic in the Optional Reading table for Lecture 4 3. Look at the prep work for Lecture 5 ahead of tomorrow’s lecture 42  11/11/2024 Thank you for your attention, engagement and contributions! 43