AUDITORY SYSTEM AND TEMPORAL LOBE FUNCTION

polymodal pathway

- connections from both visual and auditory association areas, goes to the STS - helps with stimulus categorization/classification

transduction of sound

- each hair cell is tuned to a specific frequency - cells tuned to high frequencies are located together at the base of the cochlea and as you move away from the base and towards the apex, you find cells tuned to lower frequencies.

subcortical temporal lobe structures

-Limbic cortex -Amygdala -Hippocampal formation -beginnings of fornix emotion, memory, and taste

temporal lobe functions

1. audition 2. emotion/emotional coloring 3. learning/memory (particularly spatial) 4. visual object (and movement) recognition

boundaries of temporal lobe

1. posterior cingulate gyrus - seperates the ventral parietal lobe and the temporal lobe medially 2. sylvian fissure - boundary between temporal and frontal lobe; also sepereates parietal and temporal

symptoms of temporal cortex lesions

1. problems with speech perception - location: typically left hemisphere, but not always 2. tone perseption and prosody (melody of speech) - location: largely lateralized to the right hemisphere over the left hemisphere, since right is better equipped for pitch, but again not always 3. problems with tone deafness and lack of rhythm (music problems) - location: largely right lateralized for tone issues; debate about where rhythm is lateralized, most likely left 4. auditory hallucinations - will be discussed in later modules 5. learning and memory problems - left: problems verbal material since language is largely left lateralized - right: non-verbal memory- faces/tunes/shapes, etc. 6. Affective problems/emotional processing, including loss of fear (especially if amygdala is impacted) - location: typically right lateralized 7. Difficulty categorizing things such as giving an object a verbal label; largely a language issue - location: probably left bc language processing

speech frequencies

100-8,000 Hz

frequency range

50-16,000 Hz

two streams hypothesis

A model of the neural processing of vision as well as hearing. As visual information exits the occipital lobe and sound leaves the phonological network, it is divided into two streams. 1. The ventral (what) stream goes to the temporal lobe and is involved with object identification and recognition. 2. The dorsal (where) stream goes to the parietal lobe and is involved with processing the object's spatial distance relative to the viewer.

temporal lobe

A region of the cerebral cortex primarily responsible for hearing and language.

basilar membrane

A structure that runs the length of the cochlea in the inner ear and holds the auditory receptors, called hair cells.

dorsal auditory pathway

ACTION STREAM - from auditory cortex to posterior parietal for integration - job to map the auditory sensory representations onto articulatory motor representations. (phonology)

Brodmann's division of the temporal lobe

BA 41, 42, and 22.

ventral auditory pathway

PERCEPTUAL STREAM phonemes are processed posteriorly to syllables and environmental sounds. the information then joins the visual ventral stream at the middle temporal gyrus and temporal pole. Here the auditory objects are converted into audio-visual concepts (semantics)

tympanic membrane

The eardrum. A structure that separates the outer ear from the middle ear. The sound wave vibrates the tympanic membrane, just as percussionists mallet makes the head of a tympani drum vibrate. This vibration is then passed through and amplified by a series of 3 small bones called the ossicles.

Ventral stream of vision

WHAT PATHWAY leaves V1 in the occipital lobe and moves ventrally down into the temporal lobe. travels through BA 37, 21, 20, 38 This pathway is responsible for object identification, including processing stimulus features like color and shape.

Dorsal stream of vision

WHERE PATHWAY leaves V1 and moves in a dorsal direction, up towards and into the parietal lobe. This pathway is responsible for processing the location of objects in space, spatial relationships between objects, and movement through space

fusiform gyrus

brain area of the inferior temporal cortex; it's not just occipital, not just faces - Color processing - Face recognition - Body recognition - Word recognition - Identification of features within each category

Fornix System

bundle of nerve fibers; important output tract of the hippocampus. It is considered as the main connecting tract of the limbic system. Being a part of the limbic system is associated with the processes of memory, emotions and sexual responses.

job of the outer ear

catches sounds

Cochlear Scalae

cochlear chambers - fluid filled canals in which the fluid circulates; fluid pulse in time with the auditory signal (think waves) scala vestibuli scala media - where the magic happens for transduction scala tempani

ear anatomy

complex and designed to capture sound

job of inner ear

convert sounds to action potentials on the auditory pathway going to the brain

inferotemporal cortex

cortex of the inferior temporal lobe - acts to do the ventral and STS stream functions AND also to integrate vision and audition

sensorineural deafness

deafness that usually results from damage to the inner ear or to the auditory nerve (damage to cochlea, CN VIII)

medial temporal projection

from overlying cortex into the hippocampus and maybe amygdala for emotional coloring - memory - Stimulation recognition - The familiar conscious experience of knowing, assimilating, and feeling

tuning curves

graphs of individual auditory nerve fiber responses - show a cell's response to various frequencies - done by fMRI machine, frequency tones played at different frequencies - mostly done in animal models - bottom of each curve is the characteristic frequency, or the frequency the neuron responds to best

auditory receptors

hair cells of the inner ear that receive auditory signals; each cell has a receptive field which is a particular sound frequency, unlike a visual receptor which is a point in space

BA 22

higher order auditory or the parabelt area

sound frequency

how often do we cycle between a period of compressed air and rarified air - the number of peaks per second called frequency of the sound - measured in Hz - low frequency , low pitch - less peaks - high frequency, high pitch - more peaks

echolocalization

identifying and locating objects by bouncing sound waves off them

localization

identifying the source of air-pressure waves

tonotopic representation

in which different points of the basilar membrane represent different sound frequencies, also applies to the auditory cortex: there, too, different locations represent different sound frequencies

cochlea

inner ear which contains the auditory sensory receptors called hair cells; snail shell-shaped structure, behind the tympanic membrane and the ossicles - where transduction happens - has three fluid filled canals/chambers

insular lobe (insula)

is revealed by deflecting the temporal lobe and lies deep in the lateral sulcus

STS stream

leaves V1 and moves into a specific location in the temporal lobe called the superior temporal sulcus (hence the abbreviation, STS). - processes biological motion

amygdala

limbic system structure involved in emotion, especially fear and aggression

tonotopic maps

link brain areas to types of auditory stimuli they process

primary auditory cortex organization

located in the temporal lobe, tucked away in a gap between the outer temporal lobe and the insular cortex- heschl's gyrus - tonotopic: neurons like different tones; it's a gradient - anterior to posterior, neurons get tuned to gradually lower frequencies

long term depression

long-lasting decrease in synaptic effectiveness after low-frequency electrical stimulation

sound

made by compressed and rarified air particles - sound is a wave

temporal cortex lesions

many deficits have to do with sound and hearing, but not all; many are also associated with language, as the temporal lobe is the major hub for language

Semantics

meaning of words and sentences

compressed air particles

means air particles are closed together. - peak in the sound wave

rarified air particles

means the air is spread out - low in the sound wave

auditory degeneration with aging

occurs in the inner ear, auditory nerve, and brain

conductive deafness (middle-ear deafness)

outer and middle ear damage; hearing loss that occurs if the bones of the middle ear fail to transmit sound waves properly to the cochlea

Pinna

outer ear, external structure which acts like a funnel for sound. it catches waves of air pressure and directs them into the external ear canal, which amplifies them somewhat and directs them into the eardrum at its inner end. All the little folds inside your ear are specifically designed to help move sound into the ear canal and to help amplify certain frequencies!!

BA 41

primary auditory cortex (A1)

stria vascularis

responsible for bloodflow and the fluid that travels through the scalae

BA 42

secondary auditory cortex or the belt area

tectorial membrane

sits on top of the hair cells

three ossicles

smallest bones in your body. malleus (hammer), incus (anvil), stapes (stirrup) - also vibrate with tympanic membrane make contact with the oval window and push on it

hair cells

specialized auditory receptor neurons embedded in the basilar membrane

hierarchal sensory pathway

Function: integrate auditory and visual information

Amplitude

Height of a wave, tells us about intensity - high amplitude, high intensity = loud sound - low amplitude, low intensity = quiet sound - loudness of sound measured on dB - pain threshold - 120 dB - damage threshold (which if surpassed can do permanent damage) is actually lower than the pain threshold

Lange & Lappe, 2006

the STS stream responds not just to people or animals, but stick figures and other images that resemble biological motion

audition

the ability to construct perceptual representation from pressure waves in the air, includes localization and echo-localization, as well as the ability to detect the complexity of pressure waves

pitch

the highness or lowness of a sound, affected by the frequency of peaks

oval window

the membrane at the entrance to the cochlea through which the ossicles transmit vibrations

Organ of Corti

the membrane in the cochlea that separates the scala media and scala tempani - complex structure of cells - where transduction takes place - held by the basilar membrane - has inner and outer hair cells

Timbre

the quality of a sound wave that derives from the wave's complexity - is not really measured by the sound wave

primary auditory cortex

the region of the superior temporal lobe whose primary input is from the auditory system

Phonology

the sound system of a language

tone-based hearing tests

will NOT pick up every type of hearing loss!!

central deafness

a hearing impairment in which the auditory areas of the brain fail to process and interpret action potentials from sound stimuli in meaningful ways, usually as a consequence of damage in auditory brain areas (upstream of VIII)

tinnitus

a jingling; ringing or buzzing in the ear -leading service-related disability

Hippocampus

a neural center located in the limbic system; helps process explicit memories for storage

heschel's gyrus

all auditory information is projected here

job of middle ear

amplifies sounds

tonotopic organization

an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency - THIS TYPE OF ORGANIZATION IS NOT EXCLUSIVE TO HUMANS

long-term potentiation

an increase in a synapse's firing potential after brief, rapid stimulation. Believed to be a neural basis for learning and memory.

limbic system

associated with emotions such as fear and aggression and drives such as those for food and sex. Includes the hippocampus, amygdala, and hypothalamus.

frontal lobe projection

auditory and visual cortex to the frontal lobe -movement control -short-term memory -affect