Neurobiology of Hearing… Introduction UCHC-INCYL-USAL 2019 David Pérez González Hearing . Far-range sense: like vision . Omnidirectional Essential for communication of animal and men Sound: quick variations of pressure Compressed air Rarefied air pressure Air One Distance cycle Sound and Sound propagation Wavelength Sound Amplitude pressure Wavelength λ C = λ * ν (~ 330m/s) ν = Frequency = number of cycles/s (Hz) Properties of a sine wave • Frequency: Cycles per second, or Hertz (Hz). • Phase: angle (degrees). • Amplitude: decibels (dB) Sound frequency and intensity Low frequency High frequency Air Air pressure Low intensity High intensity Air Air pressure Distance Distance Sound pressure level 200,000,000 • The difference in amplitudes between the quietest and loudest sounds we can hear is massive • Normal air pressure: 100k Pascals. • We can hear a .000000001% change in pressure. 20 Sound pressure level 140 • The decibel scale: the logarithm of a ratio (relative to 20µPa): 20log 10(p/ 20µPa) 20µPa 0dB SPL 200µPa 20dB SPL 2000 µPa 40dB SPL etc. 0 Decibel Scale • Relative • Logarithmic I p dB SPL = 10 log 10 = 20 log 10 I0 p0 -5 • Reference pressure p0 = 2x10 Pa (hearing threshold 1kHz) Auditory thresholds in humans (dB) Threshold of pain Speech Sound intensity Absolute threshold Sound frequency (kHz) Mammalian audiograms Pure tones and complex sounds aaa Zeit The auditory information arriving at the ears is a mixture of all the sounds in the environment. The individual sound waves are combined into a single, complex sound wave. The peripheral auditory system Function of the Middle Ear Transformation: Pressure p Area: Al : As = 17 : 1 Lever deflexion d : lm : li = 1,3 : 1 combined: d / p = 22 : 1 p / d = z * ω = Impedance * Frequency The Inner Ear (Bony Labyrinth) Vestibular Nerve Cochlea Sacculus Travelling wave in the Cochlea Travelling wave in the Cochlea Low Frequency Travelling wave in the Cochlea High Frequency Frequency Analysis in the Cochlea Pelicula cochlea The cochlea Organ of Corti 30 Detail of the organ of Corti: IHC OHC Hair cells: transduction QUIETSOUND Hair cell depolarization Hair cell depolarization • The movement of the cilia produces changes on the membrane potential Inner and outer hair cells Inner hair cell Outer hair cells Stimulus propagation Amplification Effect of sound on a outer hair cell ¿What is the role of outer hair cells? Hearing loss Hair cell innervation The human auditory brain Kiang and Peake (1988) The cochlear nucleus is the first step into the central auditory system Cochlear nuclei Auditory nerve Cochlea Cytoarchitecture of the cochlear nuclei. Golgi staining Cytoarchitecture of the cochlear nuclei. Golgi staining The cochlear nuclei: parallel processing pathways Superior olivary complex Mechanisms for sound localization in the horizontal plane (azimuth) Time and intensity differences for localizing a sound source Interaural time differences (ITDs) Interaural level differences (ILDs) Mechanisms for sound localization in the vertical plane (elevation) Structure of DC the inferior colliculus CN • Central nucleus (CN) LC • Dorsal cortex (DC) • Lateral cortex (LC) FUNCTIONAL PROPERTIES OF THE INFERIOR COLLICULUS FUNCTIONAL PROPERTIES OF THE INFERIOR COLLICULUS Inputs to the Inferior Colliculus Inputs from Cochlear Nucleus INFERIOR IC COLLICULUS DLL DLL VLL VLL Monaural inputs to IC DCN DCN Monaural inputs to SOC and IC VCN VCN LSO MSO MSO LSO CONTRA IPSI Inputs from SOC INFERIOR IC COLLICULUS DLL DLL VLL VLL ITDONLY DCN ILD DCN - ITD VCN ILD-ITD VCN LSO MSO MSO LSO CONTRA IPSI Inputs from Lateral Lemniscus INFERIOR IC COLLICULUS DLL ILD-ITD DLL VLL VLL Monaural DCN DCN VCN VCN LSO MSO MSO LSO CONTRA IPSI CONTRA Frequency Band Lamina IPSI INFERIOR COLLICULUS DLL VLL Monaural DCN VCN LSO MSO Binaural MSO LSO Inputs Create Functional From Loftus et al (2010) J Neurosci • Zones in the IC 30(40):13396 –13408 The organisation and function of the auditory thalamus From Bear Connors and Paradiso: Neuroscience, Exploring the brain The human auditory system Auditory cortex Medial geniculate body (Thalamus) Inferior Dorsal cochlear colliculus nucleus Ventral cochlear nucleus Lateral lemniscus (Adapted from Bear et al) Cochlea Superior olive Spiral ganglion Medial geniculate body D Auditory cortex Thalamic reticular nucleus M L V MGD IC (dorsal cortex) IC (external cortex) MGM Superior Colliculus VNLL MGV Po DNLL Cochlear nucleus Spinal cord IC (central) Circuits for auditory fear conditioning Auditory cortex Amygdala Central MGM MGV Lateral Defence responses Behaviour Hypothalamus / pituitary Autonomic nervous Conditioned stimulus -tone system The auditory cortex Location of auditory cortex in human brain Planum Temporale Primary auditory cortex: Heschl’s gyrus Neurons and layers of rat auditory cortex Neurons and layers of rat auditory cortex The auditory cortex in mouse and cat Multiple tonotopic maps in the cortex Rostral Caudal Petkov et al 2006 Plasticity in the auditory cortex Plasticity in auditory cortex following stimulation of nucleus basalis in rat Reorganisation of the frequency map in rat A1 following nucleus basalis stimulation Kilgard et al 1997 Science 279 1715 .