1 Psychology 304: Brain and Behaviour Lecture 27

2 Announcement Please note that course evaluations are available online. If you have not received an directing you to the evaluations for this course, you may provide your evaluation at: Course evaluations will be available until December 5 th. Your feedback is extremely valuable—both to the Psychology Department and to me. 2

3 From last class …. (a) primary somatosensory cortex (SI): Contralateral processing. (b) secondary somatosensory cortex (SII): Bilateral processing. (d) somatosensory association cortex (posterior parietal lobe): Vision and touch, as illustrated by “asomatognosia.” Functions of the:

4 The Auditory System 1. What is the structure of the ear and where are the receptors for sound? (continued) 2. How is information about sound relayed to the brain? 3. What are the major areas of the brain that are associated with the perception of sound?

5 By the end of today’s class, you should be able to: 1. describe the structural and functional features of the outer, middle, and inner ear. 2. explain how an action potential is generated in the afferent nerve fibres of the auditory system. 3. review the pathway by which auditory information is transmitted from receptors to the brain.

6 4. identify the locations and functions of the primary cortex, secondary cortex, and association areas for the auditory system.

7 What is the structure of the ear and where are the receptors for sound? (continued) The organ of Corti contains the receptors for sound.

8 The Receptors for Sound

9 Cochlea Slice

10 Hair Cells Images Cilia of Outer Hair CellsCilia of Inner Hair Cells

11 Inner Hair Cells Outer Hair Cells Inner and Outer Hair Cells

12 Hair Cell Contact with the Tectorial Membrane Auditory nerve

13 Tip Links 13

14 Place theory and volley theory have been proposed to explain the how sound receptors facilitate the perception of pitch. Tonotopic organization is found at all levels of the auditory system (e.g., cochlea, inferior colliculi, auditory cortical regions).

15 Tonotopic Organization

16 When hair cells are stimulated, action potentials are triggered that pass down axons of the auditory nerve—a branch of cranial nerve VIII. The vibrations of the cochlear fluid are ultimately dissipated by the round window.

17 The Structure of the Ear

18 How is information about sound relayed to the brain? Sound information is relayed to the brain via a network of auditory pathways.

19 Pathways of the Auditory System

20 What are the major areas of the brain that are associated with the perception of sound? The majority of thalamic neurons that receive sound information subsequently project the information to the primary auditory cortex. Thereafter, information is projected to the secondary auditory cortex (SII) and association areas.

21 Auditory Areas of the Brain

22 Current theory suggests two large areas of auditory association cortex: the prefrontal cortex and the posterior parietal cortex. The anterior auditory pathway leading to the prefrontal cortex is thought to be involved in identifying sounds (“what”); the posterior auditory pathway is thought to be involved in locating sounds (“where”).

23 Pathways to Auditory Association Cortex

24 The Auditory System 1. What is the structure of the ear and where are the receptors for sound? (continued) 2. How is information about sound relayed to the brain? 3. What are the major areas of the brain that are associated with the perception of sound?