Audition

eardrum, vibrates with sound waves and transmits to bones in middle ear

malleus, incus, stapes stapes vibrates against membrane of cochlea

• part of inner ear • filled with fluid • snail-shaped

• receptive organ inside the cochlea - consists of basilar membrane, hair cells, and tectorial membrane

• auditory receptor cells • contain cilia between basilar membrane and tectorial membrane • vibration causes these membranes to flex back and forth sending “waves” through the inner ear fluid causing cilia to bend (like kelp swaying). Bending in hair cells results in action potential in neurons going to cochlear nerve to auditory nerve (cranial nerve 8)

Tonotopic representation - Different parts of basilar membrane respond to different sound frequencies (tones), low to high Specific parts of the basilar membrane project to specific parts of the brain stem nuclei

Auditory pathways are majority (75%) contralaterally mediated - Auditory nerve to cochlear nuclei and superior olivary complex in medulla, where perception of sound location is processed - From medulla to inferior colliculus - to medial geniculate body in thalamus - to primary auditory cortex (core) in superior temporal lobe in the lateral fissure - to auditory association cortex (belt, parabelt) Auditory input also goes to cerebellum and reticular formation

• primary auditory cortex - divided into 3 zones that receive input from 3 different areas of medial geniculate body

• first level of auditory association cortex • At least 7 divisions • Receives input from primary auditory cortex and medial geniculate body

• “highest level” of auditory association cortex - Receives input from belt and medial geniculate body

• From posterior parabelt to the posterior parietal cortex - mediates sound localization (where)

• From anterior parabelt to anterior temporal and inferior frontal • mediates analysis of complex sounds (what)

• Discriminating the identity of multiple sounds heard simultaneously is based on pattern recognition (we don’t know how) • Pattern recog occurs in primary and association auditory cortex • Different neurons in auditory cortex are arranged in columns (like visual cortex) that respond to different properties of sound stimulus: • onset or cessation of sound, or both • changes in pitch or intensity, sometimes only in one direction • combinations of frequencies (i.e. complex stimuli) • specific frequencies only in certain contexts – i.e. if it occurs at the beginning or end of a sequence

Does not produce deafness Impairs ability to distinguish rapidly/simultaneously occurring sounds - sound location, identity and/or movement a. sound location = dorsal auditory association cortex b. sound identity = ventral auditory association area Auditory agnosia - L lesions result in impaired speech content comprehension - R lesions result in impaired speech prosody comprehension (and comp of non-speech sounds)

Specific parts of the basilar membrane project to specific parts of the brain stem nuclei - which project to specific parts of the inferior colliculus - to specific parts of the medial geniculate body - to specific parts of the primary auditory cortex Different tones are processed in different modules