lecture 6 - auditory/sensory Flashcards
sensory system characterized by (3 things
hierarchical organization
functional segregation
parallel processing
describe hierarchical organization of sensory system
damage to each area?
top down or bottom up flow of info?
- low level processing at primary, move up levels = more complex.
ranked: receptor -> primary -> secondary -> association
organized by functional complexity: simple,general -> complex, specific
damage to low level = loss of function. damage to higher level = specific sensory deficit
sensory info goes bottom up, but can use top-down to hone in on what youre looking for and inhibit detection of things youre not looking for.
sensation vs perception
detecting stimuli = sensation
interpreting stimuli = perception
agnosia
cant ID object but can interact. perceptual problem
functional segregation of sensory systems
different processes/functions processed in different areas.
parallel processing of sensory systems
various systems have overlapping pathways and cross talk between them
- influence behaviour without conscious awareness
- influence behaviour by engaging conscious awareness.
the binding problem
how do we perceive anything as a whole?
all perceptions must be combined somewhere. => claustrum. thin layer of neurons under neocortex. very top of sensory hierarchy.
how do we hear sound?
vibration of air molecules transduced into auditory information
3 important aspects of waves
amplitude = loudness frequency = pitch complexity = timbre
pure tones
one sine wave. not naturally made
cant localize, uncomfortable to listen to
complex sound waves
complex addition of waves.
what is fourier analysis
mathematical breakdown of complex waves in to component sine waves
- theory that auditory system does fourier analysis
perceiving pitch = fundamental frequency or missing fundamental frequency
fundamanteal frequency = the highest frequency of the bunch is the one detected.
missing : beat frequencies present in all sounds. when fundamental is not there, the beat frequency is still present so fundamental fequency can be perceived.
outer ear - transmission of sound waves into ear.
sound waves travel down auditory canal tympanic membrane (eardrum) vibrates. vibration transferred to ossicles - malleus, incus, stapes. stapes knocks oval window (inner ear) - pushes liquid inside cochlea, causing movement in organ of corti inside cochlea.
inner ear
transfers vibrations to perilymph of cochlea (long, coiled tube with internal membrane)
internal organ of corti - holds hair cells = transducers. filled with fluid = endolymph.
organ of corti
2 membranes
basilar membrane: hair cells mounted on this one.
tectorial membrane - rests on hair cells.
round window
dissipates vibrations and the end of the cochlea.
organ of corti - where frequencies fall on organ.
white noise
tonotopic map
higher frequency = hair cells by oval window
lower frequency = by tip of basilar membrane
white noise = all component frequencies at equal amplitude.
tonotopic map - carried by auditory nerve. to temporal. each level of auditory system organized by frequency.
how hair cells respond to sound
on tip of hair cell = cilia. connected to adjacent cilia via tip link which is attached to cation channel.
the cilia increase in length along axis. only tallest touches tectorial membrane. when sound comes thru, tectorial membrane moves ( perilymph above) and shears hair cell. mechanical movement of cilia causes conformation change in tip link opening K influx. K+ influx induced VG-Ca2+ channel to open which releases NT on auditory nerve.
outer hair cells
- attach to tectorial membrane. help mediate auditory attention.
make membrane looser is you dont want to hear frequency. make membrane tighter if you do want to hear frequency.
== top- down control on organ of corti by brain.
essential for normal hearing
endolymph
fluid in organ of corti. rich in K+. energy storage.
ear to A1 pathway
organ of corti -> auditory nerve -> cochlear nucleus (ipsilateral) -> superior olives (combined input), inferior colliculus -> medial geniculate nucelus (thalamus) -> A1
- Lots of auditory processing in brainstem region.
sound localization - lateral and medial superior olives - their functions.
lateral superior olives = notices differences in loudness between info from both ears
medial = responds to difference in time of arrival when comparing info from both ears.
use these two areas to localize sound.
superior olives project to colliculi in the midbrain - inferior & superior
inferior colliculi: high level auditory processing, ID sounds
superior colliculi: coordinates eye movements to orient selves in response to sound.
superior colliculi is retinotopically organized map of auditory space. *info from olives tells where you are, colliculi mediates movement of eyes toward that sound.
A1 and A2
A1 = organized into functional columns. vertical neurons respons to same frequency.
tonotopic map. - fourier analysis probabbly done at this point already
A2 - adjacent to A1. organized by frequency. used to understand speech.
auditory association cortices
PFC
PPC
PFC - anterior auditory pathway. “what” ID sounds.
PPC - posterior auditory path. “where” locate sounds, help prep for action.
auditory and visual interaction - in assoc cortex
PPC - 2-ary for V and A. mutli-modal area. integral in sensory processing
damage to auditory system
auditory cortex damage is rare if it does occur. its hidden in a fissure so its harder to damage.
there are less severe permanent deficits if damaged alone because subcortical circuits are doing a lot of complex things.
deafness = conductive, nerve
damage to inner or middle ear.
conductive deafness = damage to ossicles, eardrum
nerve deafness = originates from nerve damage. ex: loss of hair cell receptors.
cochlear implants
help with deafness = bypass hair cell damage. converts sound to electrical signal and carries directly to auditory nerve.
tinnitus
damage to auditory system . constant, whirr, buzz. not debilitating usually.
continues despite auditory nerve cuts = suggest product of central processing.
somatosensations - define
sensation from body
somatosensory system - 3 systems
exteroreceptive - applied to skin
proprioceptive - monitor position of body
interoceptive - general info on bodily conditions
cutaneous receptors - what are they, what do they do and 4 examples
receptors embedded in skin. skin deforms or changes chemistry of receptor to change ion permeability.
mechanical transduction = mechanical change in cell receptor = transduction
free nerve ending - multimodal: pain,temp
pacinian corpuscle: mechanoreceptor - pressure. rapidly adapting, cannot sense constant pressure
merkels and ruffini: adapt slowly, sense constant pressure.
indentation - merkel. stretch - ruffini
fast vs slow adaptation of cutaneous receptors
fast = after few milisec stop firing to stimulus.
slow - after few milisec continue firing. slower, less frequent but still fire as long as stimulus present.
stereognosis
identify by touch. manipulate object in hands to change stimulation pattern of receptors.
dermatomes
areas of body innervated by dorsal roots on given section of spinal cord.
dermatomes overlap, not a clean line between the 2.
2 major somatosensory pathways.
dorsal column medial lemniscus - carry touch & proprioception.
travel ipsilaterally and decussates on dorsal column nuclei (medulla). synapses on ventral posterior lateral on thalamus then to s1. some neurons bypass s1 and go to s2.
anterolateral system - carry temperature and pain. second order decussate. ascend into brain contralaterally.
anterolateral system has how many tracts?
3 tracts
spinothalamic - project to VPL -> s1
spinoreticular -> to reticular formation -> s1
spinotectal -> to tectum of thalamuc for colliculi, then to nucleus of thalamus.
VPL
receiving input from 3 branches of trigeminal nerve. carry info from contralateral side of face.
lesions of thalamus -
VPL
intralaminar & parafiscular
CPL - receive in put from dorsal system and spinothalamic = less of sensation of touch, sharp pain, temp.
no effect on chronic pain
intralaminar - receive input from spinoreticular - reduce deep chronic pain. risky bc such small area.
no effect on cutanesou sensitivity.
somatosensation in cortex
penfield mapped on post central gyrus. = orgnaized somatotopically. somatosensory homunculus. - distorted. large area dedicated to parts of body with finest tactile discrimination.
columnar organization -somatosensation
4 functional strips
- touch, pressure, heat, pain.
horiontal = prefer all type of tacile stimuli in same part of body
vertical - same part of body, same stimulus.
move antierior to posterior = more complex
s2 - organization, input,
also somatotopic organization. extends into lateral fissue. most input from s1, can receive from thalamus too.
input from both sides of body. goes to PPC
somatosensory processing streams
dorsal: s1 -> PPC.
multi sensory integration. PPC = intention and direction attention. further projects to frontal cortex
ventral: s1 -> s2. perceptions of object by shape.
damage to somatosensory cortex
mild bc ability to by-pass s1. minor contralateral deficits. deficit in stereognosis.
bilateral deficits only if part of s2 is lesioned.
PPC - bimodal neurons
bimodal = respond to activation of 2 different sensory systems. only activate if both present simultaneously.
receptive fields spatially related. if move hand into visual field - activate bimodal neuron from better visual processing.
astereognosia
inability to ID objects by touch. rare – need massive destruction of s1 and s2
asomatognosia
failure to recognize one’s own body parts.
usually unilateral - affect left side = right PPC damage.
component to contralateral neglect.
often have anosognosia as well = failure to recognize own symptoms.
rubber hand illusion
rubber hand and own hand - similar proprioceptively, given same stimulus. evetnually, hammer to rubber hand only = pull away stimulus by participant hand. rapid neuroplasticity.
perception of pain
paradoxical
- adaptive; correct what we’re doing to stop causing potential harm. respond to potentially harmful stimuli.
lack of clear cortical respresentation.
- no special/clear stimulus -> response ; very subjective.
no cortical areas necessary for pain perception.
cortical representations of pain
anterior cingulate cortex (ACC)
likely involved in emotinoal reaction, behavioural adaptations, to pain rather than pain stimuli itself.
descending pain control
pain suppressed by cognitive and emotional factors. top-down process.
suppress in good mood, when distracted. enhance pain when mad/sad
gate control theory of pain - assoc brain region?
ability of cognitive and emotional factors to suppress pain.
stop incoming brain at spinal cord/low brainstem
Periaqueductal grey (PAG) - high endorphin production. close to ventricles = endorphin straight to brain. stimulates raphe nucleus (5-HT area) which projects to dorsal column neurons carrying pain info & inhibits them
neuropathic pain
bad side to neuroplasticity.
severe chronic pain in absence of painful stimuli.
develops after injury, mechanism unknown
chemical senses
smell (airborne) taste (solution in cavity) monitor chemical content in enviro and work together to produce flavour.
other factors invovled in flavour. where is flavour processed?
temp, look, full-ness, texture, past experience.
need smell to taste.
processed in orbital frontal cortex
phermones - in animals and humans
animals: influence phsyiology and behaviour in conspecifics. regulate social interaction. huge in sex.
humans = no real evidence that phermones have effect on us.
olfactory receptors - organization, passage up
randomly organized in mucosa.
dendrites = receptive part. axon - carried thru cribriform plate (porous bone). synapse on glomeruli.
glomeruli in olfactory - organization
glomeruli kinda organized. each olfactory recptor type will synapse on same glomeruli.
how is odour identified?
component processing.
olfactory neuron replacement
replace deteriorated ones every day-few weeks.
chemotopic organization
chemical mapping in brain. symmetry in glomeruli.
different odors produce different spatial patterns of activity in bulb.
olfactory bulb. where does it project.
neurons project thru olfactory tract to amygdala) and piriform cortex = O1 (outside of amygdala)
frontal cortex (orbital frontal cortex)
hypothalamus/amygdala
hippocampus
2 major olfactory pathways
project to limbic system - mediate emotional response to odor
medial dorsal nuclei of thalamus to orbitofrontal cortex - conscious percetption to odors.
gustatory system
taste receptors in oral cavity, lungs, throat, esophagus.
one presynaptic receptor cell in taste bud synapse onto sensory nerve. rest of cells communicate via gap junctions.
replaced every few weeks.
5 tastes
umami - glutamate. 1 GPCR. sweet - 2 GPCR, salt - ion channel. bitter = 30 types of GPCR sour - unclear, maybe proton
gustatory pathways
leave the mouth via cranial nerves. facial vagus glossopharyngeal project to G1 - insula in lateral fissure then to G2 in orbitalfrontal cortex -meet with smell.
broad tuning vs narrow tuning
braod = each taste bud responsds to range of tastes; cortex = many neurons to respond to odor, texture, temp, taste. chemotopically organized. g2 - doesnt fire if satiated.
narrow tuning - specific receptor. each receptor responds to one/few tastes
anosmia
inability to smell. shears olfactory nerves that pass through cribriform plate.
aguesia
inability to taste.
rare bc many parallel pathways. due to damage in facial nerve.
selective attention
- improves perception of stimuli in focus & dampens perception of irrelevant stimuli.
2 ways to focus attention
- endogenous attention: internal cognitive processes. top-down
- exogenous attention: external events. bottom- up.
role of eye movements
covert vs overt attention
helps focus, shift attention
covert = shift attention w/o shift in eye movement
overt = shift in attention with shift in gaze
cocktail party phenomenon
allocation of resources. focus on one convo, brain block other stimuli from conscious awareness, but still unconsciously monitor for important stimuli
change blindness
blind to change (between 2 pics, for example) - no memory of parts we didnt attend to.
what is attention good for? (3)
- save resource. ignore irrelevant stimuuli
- facilitate downstream processing. ignore irrelevant signals
- speed correct output.
neural areas associated with visual attention
PPC
PFC - top down mediation.
plasticity in receptive fields
receptive field shifts towards point in visual field where stimulus should appear.
receptive fields in ventral stream shrink to be size of object of focus
simultagnosia
difficulty attending to more than one object at a time. = damage to dorsal stream
