1. Slide 1 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Bear: Neuroscience: Exploring the Brain 3e Chapter 11: The Auditory and Vestibular Systems

2. Slide 2 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Introduction Sensory Systems Sense of hearing, audition Detect sound Perceive and interpret nuances Sense of balance, vestibular system Head and body location Head and body movements

3. Slide 3 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Nature of Sound Sound Audible variations in air pressure Sound frequency: Number of cycles per second expressed in units called Hertz (Hz) Cycle: Distance between successive compressed patches Range: 20 Hz to 20,000 Hz Pitch: High and Low Intensity: Difference in pressure between compressed and rarefied patches of air

4. Slide 4 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Structure of the Auditory System Auditory System

5. Slide 5 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Structure of the Auditory System Auditory pathway stages Sound waves Tympanic membrane Ossicles Oval window Cochlea fluid Sensory neuron response Brain stem nuclei output Thalamus to MGN to A1

6. Slide 6 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Components of the Middle Ear The Middle Ear

7. Slide 7 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Sound Force Amplification by the Ossicles Pressure: Force by surface area Greater pressure at oval window than tympanic membrane, moves fluids The Attenuation Reflex Response where onset of loud sound causes tensor tympani and stapedius muscle contraction Function: Adapt ear to loud sounds, understand speech better The Middle Ear

8. Slide 8 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Inner Ear Anatomy of the Cochlea Perilymph: Fluid in scala vestibuli and scala tympani Endolymph: Fluid in scala media Endocochlear potential: Endolymph electric potential 80 mV more positive than perilymph

9. Slide 9 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Physiology of the Cochlea Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out The Response of Basilar Membrane to Sound Structural properties: Wider at apex, stiffness decreases from base to apex Research: Georg von Békésy Endolymph movement bends basilar membrane near base, wave moves towards apex The Inner Ear

10. Slide 10 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Organ of Corti and Associated Structures The Inner Ear

11. Slide 11 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Transduction by Hair Cells Research: A.J. Hudspeth. Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward The Inner Ear

12. Slide 12 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Innervation of Hair Cells One spiral ganglion fiber: One inner hair cell, numerous outer hair cells Amplification by Outer Hair Cells Function: Sound transduction Motor proteins: Change length of outer hair cells Prestin: Required for outer hair cell movements The Inner Ear

13. Slide 13 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Central Auditory Processes Auditory Pathway More synapses at nuclei than visual pathway, more alternative pathways Anatomy Dorsal cochlear nucleus, ventral cochlear nucleus, superior olive, inferior colliculus, MGN, lateral lemniscus, auditory nerve fiber Primary pathway: Ventral cochlear nucleus to superior olive to inferior colliculus to MGN to auditory cortex

14. Slide 14 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Response Properties of Neurons in Auditory Pathway Characteristic frequency Frequency at which neuron is most responsive Response More complex and diverse on ascending auditory pathway in brain stem Central Auditory Processes

15. Slide 15 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Encoding Sound Intensity and Frequency Encoding Information About Sound Intensity Firing rates of neurons Number of active neurons Stimulus Frequency, Tonotopy, Phase Locking Frequency sensitivity: Basilar membrane Frequency: Highest at base, lowest at cochlea apex Tonotopy: Systematic organization of characteristic frequency within auditory structure

16. Slide 16 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Phase Locking Consistent firing of cell at same sound wave phase Encoding Sound Intensity and Frequency

17. Slide 17 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Techniques for Sound Localization Horizontal: Left-right, Vertical: Up-down Localization of Sound in Horizontal Plane Interaural time delay: Time taken for sound to reach from ear to ear Interaural intensity difference: Sound at high frequency from one side of ear Duplex theory of sound localization: Interaural time delay: 20-2000 Hz Interaural intensity difference: 2000- 20000 Hz Mechanisms of Sound Localization

18. Slide 18 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Sensitivity of Binaural Neurons to Sound Location Monaural: Sound in one ear Binaural: Sound at both ears Superior olive: Cochlear nuclei input to superior olive, greatest response to specific interaural delay Mechanisms of Sound Localization

19. Slide 19 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Mechanisms of Sound Localization Delay Lines and Neuronal Sensitivity to Interaural Delay Sound from left side, activity in left cochlear nucleus, sent to superior olive Sound reaches right ear, activity in right cochlear nucleus, first impulse far Impulses reach olivary neuron at the same time  summation  action potential Localization of Sound in Vertical Plane Sweeping curves of outer ear

20. Slide 20 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Acoustic Radiation Axons leaving MGN project to auditory cortex via internal capsule in an array Structure of A1 and secondary auditory areas: Similar to corresponding visual cortex areas Neuronal Response Properties Frequency tuning: Similar characteristic frequency Isofrequency bands: Similar characteristic frequency, diversity among cells Auditory Cortex

21. Slide 21 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Principles in Study of Auditory Cortex Tonotopy, columnar organization of cells with similar binaural interaction The Effects of Auditory Cortical Lesions and Ablation Lesion in auditory cortex: Normal auditory function Lesion in striate cortex: Complete blindness in one visual hemifield Different frequency band information: Parallel processing, localization deficit Auditory Cortex

22. Slide 22 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Importance of Vestibular System Balance, equilibrium, posture, head, body, eye movement The Vestibular Labyrinth Lateral line organs Small pits or tubes Function Sense vibration or pressure changes The Vestibular System

23. Slide 23 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Otolith Organs The Vestibular System

24. Slide 24 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Vestibular System The Semicircular Canals Function: Detect head movements Structure Crista: Sheet of cells where hair cells of semicircular canals clustered Ampulla: Bulge along canal, contains crista Cilia: Project into gelatinous cupula Kinocili oriented in same direction so all excited or inhibited together Semicircular canals: Filled with endolymph

25. Slide 25 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Push-Pull Activation of Semicircular Canals Three semicircular canals on one side Helps sense all possible head-rotation angles Canal: Each paired with another on opposite side of head Push-pull arrangement of vestibular axons: Rotation causes excitation on one side, inhibition on the other The Vestibular System

26. Slide 26 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Central Vestibular Pathways The Vestibular System

27. Slide 27 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Vestibulo-Ocular Reflex (VOR) Function: Line of sight fixed on visual target Mechanism: Senses rotations of head, commands compensatory movement of eyes in opposite direction Connections from semicircular canals, to vestibular nucleus, to cranial nerve nuclei  excite extraocular muscles The Vestibular System

28. Slide 28 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins The Vestibular System Vestibular Pathology Drugs can damage vestibular system Effects: Trouble fixating on visual targets Walking and standing difficult

29. Slide 29 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Concluding Remarks Hearing and Balance Nearly identical sensory receptors (hair cells) Movement detectors: Periodic waves, rotational, and linear force Auditory system: Senses external environment Vestibular system: Senses movements of itself

30. Slide 30 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins Concluding Remarks Hearing and Balance (Cont’d) Auditory Parallels Visual System Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code Convergence of inputs from lower levels  Neurons at higher levels have more complex responses

31. Slide 31 Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins End of Presentation