Similarities & Differences Between Senses

Question 1

SCHNUPP & CARR (2009); LADICH & SCHULZ-MIRBACH (2016)

Answer 1

• tympanic ears evolved eat least 5 times in vertebrate line
• bony fish ears contain sensory maculae that respond to underwater sound in directional fashion; during transition from water-land, tympanic middle ears capable of receiving airborne sound evolved separately

Question 2

MAMMALIAN EAR STRUCTURE

Answer 2

• sound arrives at tympanum; amplified in middle ear
• cochlea (inner ear) contains auditory receptor cells
  1. external ear (pinna)
  2. middle ear = ossicles; tympanic membrane (eardrum)
  3. inner ear = oval window; round window; vestibulocochlear nerve (VIII)
  4. cochlea = scala vestibuli (vestibular canal); scala media (middle canal); scala tympani (tympanic canal); oval/round window; VIII

Question 3

TONOPIC ARRANGEMENT OF HAIR CELLS

Answer 3

• aka. unrolling of cochlea
• relative amplitude of movement
• high frequencies displace basilar membrane in cochlea base
• low frequencies displace basilar membrane in apex of cochlea

Question 4

BASILAR MEMBRANE

Answer 4

• location defines which hair cells (auditory receptor cells) respond to dif sound frequencies
• cross section of Organ of Corti (aka. inner ear) = ca 20k hair cells along basilar membrane
• inner hair cells = 95% of afferent projections
• tallest stereocilia in contact w/tectorial membrane

Question 5

FETTIPLACE & HACKNEY (2006)

Answer 5

• stereocilia displaced; K+ channels stretch open; influx of K+ into hair cell
• depolarisation = receptor potential
• opening of Ca2+ channels
• influx of Ca2+ triggers neurotransmitter release to first-order auditory interneuron

Question 6

MANLEY (2000)

Answer 6

• highly schematic representation of amniote phylogenetic tree over 400 million years to illustrate approximate time of origin of particular features of auditory systems
• mammals = IHC/OHC (inner/outer hair cells); lizards = high/low frequency hair cells; birds/crocs = THC/SHC (tall/short hair cells)
  THC/SHC & IHC/OHC PARALLELS
• THCs/IHCs less specialised; receive strong afferent innervation
• OHC innervated by relatively few efferent fibers (=5%); SHC receive no afferent innervation at all

Question 7

WHY/HOW DO VISION VS HEARING DIFFER?

Answer 7

PHOTORECEPTORS
- axon terminals
- axon
- accessory structure = light-sensitive receptor molecules in membrane
INNER HAIR CELLS
- accessory structure = stereocilia w/ion-channels in membrane
- no axon/axon terminals
BOTH
- cell body w/nucleus (w/DNA)

Question 8

KONISHI (1973)

Answer 8

• sound = movement of air particles set in motion by vibrating structure
• wave characteristics of sound = alternate waves of compression/rarefaction of air; molecules move back & forth from regions of high pressure to low
• measures of sound = frequency (reciprocal of wavelength)/amplitude
• most birds hear up to 5-6kHz; barn owl = exceptional high-frequency hearing w/characteristic frequencies of 9-10kHz
• more than half of auditory neurons = sensitive in 5-10kHz range

Question 9

HEFFNER & HEFFNER (2007)

Answer 9

• audiograms = measured behaviourally; threshold for tone when correctly selected = >50%
• SPL = sound pressure level (set at 0 for 1kHz)

Question 10

DENT (2017)

Answer 10

• psychoacoustics = psychophysics subfield
• audiograms = most common assessment of animal hearing
• measurement of detection thresholds = stimuli varied in frequency/intensity played back to animal; if it responds in majority of trials correctly, stimulus = above threshold
• ie. budgies learn to peck key to start variable waiting interval; trained w/rewards/range of loud signals to respond correctly; during testing, other signal variations = interspersed; hearing = right key; if not = withhold

Question 11

MANN ET AL. (2007)

Answer 11

• electrophysiology = AEP measurements as non-invasive method for studying hearing functions
• AEP = auditory evoked potentials to determine sensitivity threshold for dif sound frequencies
• faster; no need to train animal to auditory stimuli; audiograms generated from AEPs instead of ratios of correct beh responses
• hearing in 8 Canadian freshwater fish = best in fish w/connection between inner ear/swim bladder
• dif impacts of anthropogenic noise pollution

Question 12

SUMMARY

Answer 12

• light/sound propagate as waves that differ in frequency/intensity; light = absorbed by photoreceptors as quanta; sound vibrates internal structures of ear
• spatial relations of simuli in outer world = coded through retinotopic mapping in visual pathways; spatial relations in hearing pathways = largely lost; to use sound for accurate sound source location, these need to be reconstructed in brain
• audiograms demonstrate tuning & sensitivity ranges; allow comparisons between species to determine how hearing can be adapted to dif tasks/needs

Question 13

RESEARCH IN BIRDS: INTRO

Answer 13

• research in birds contributed to fundamental demonstration of neural mechanisms relevant to human hearing
• auditory pathways have parallel/serial connections similar to vision; tonotopic maps result from arrangements of sensory interneurons in cochlea aka. important binaural comparisons & reconstruction of spatial locations relative to body

Question 14

HILL ET AL. (2010)

Answer 14

• owl moves its head to face visual/sound target
• movement in space can be represented by angular deviation in 2 directions:
  1. AZIMUTH (horizontal)
  2. ELEVATION (vertical)

Question 15

KNUDSEN, BLASDEL & KONISHI (1979)

Answer 15

• how do owls localise sound sources?
• search coil on top of owl’s head lies at intersection of horizontal/vertical magnetic fields; movememnt induces current in search coil
• first viewing direction = fixated w/sound from zeroing speaker
• head movement towards sound from target speaker = measured; accuracy determined
• head flick delay = 100ms BUT sounds of 75ms also elicit flick (open-loop condition)
• localisation accuracy = function of position of target speaker
• target speaker in front = error < 2 degrees

Question 16

KNUDSEN (2002)

Answer 16

• auditory cue values & locations in space
• precise prey localisation requires both ears
• sound waveform in right ear = delayed & attenuated relative to left ear
• correspondence of interaural timing dif (ITD) & interaural lvl dif (ILD) values w/locations in space for 6kHz sound
• spatial pattern changes for other frequencies

Question 17

OPTIC TECTUM IN BIRDS

Answer 17

• located in midbrain
• sensory info conveyed through midbrain to thalamus & further to cerebrum
• auditory midbrain = located on inner side of optic tectum (MLD aka. mesencephalicus lateralis dorsalis)

Question 18

AUDITORY PATHWAY

Answer 18

CN: cochlear nucleus
SO: superior olive
LLD: lateral lemniscus/dorsal nucleus
LLI: lateral lemniscus/intermediate nucleus
LLV: lateral lemniscus/ventral nucleus
MLd: dorsal lateral nucleus of mesencephalon
HVC: hgh vocal centre
NCM: caudal medial nidopallium
Nif: interfacial nucleus of nidopallium
RA: robust nucleus of arcopallium
E: entopallium
OB: olfactory bulb
CSt: caudal striatum

Question 19

CARR & KONISHI (1988)

Answer 19

• measuring interaural time dif (ITD) in cochlear nucleus (CN)
• axonal delay lines for time measurement in owl’s brainstem
• Jeffress model = sound location computed from difs in delay/intensity between 2 ears
• study confirmed basic premises with work on barn owls

Question 20

PARALLEL PROCESSING OF TIME (ITD) & INTENSITY (ILD)

Answer 20

• sensory neurons code both arrival time & intensity of particular sound frequency:
  1. coding of sound as spikes in sensory neurons (inner ear)
  2. separation of time/intensity data (magnocellular/angular nucleus)
  3. map of ITDs (laminar nucleus)
  4. map of ILDs (anterior/posterior lateral lemniscus aka. lateral lemniscus/hindbrain)
  5. convergency of time/intesity pathways (auditory midbrain)
  6. formation of auditory space map (external nucleus of MLD)

Question 21

LOCATION OF SOUND SOURCES

Answer 21

• mapped in 2 dimensions on MLD (midbrain & optic tectum)
• spatial reconstruction of auditory space in front of owl (L/R = azimuth degrees; +/- = elevation degrees) from ITD/ILD coding pathways converging in MLD
• inner part of auditory region neurons = organised in tonotopical layers (mapping of interneurons according to frequency tuning); outer part = interneurons tuned to 6-8kHz aka. highest sensitivity range

Question 22

GROTHE, PECKA & MCALPINE (2010)

Answer 22

• spatial mapping = projected to cortical areas aka:
  1. auditory cortex
  2. medial geniculate
  3. inferior colliculus
  4. cochlear nucleus
  5. superior olivary nucleus
  6. brainstem
  7. cochlea

Question 23

JARVIS (2019)

Answer 23

• basic auditory pathway comparison between birds & mammals
  BOTH
  hair cells -> cochlear ganglion -> cochlea nuclei -> lemniscal nuclei …
  BIRDS
  … MLd -> ovoidalis -> L2 in caudomedial pallium -> L3/L1 -> NCM & CM -> Ai & CSt
  MAMMALS
  … interior colliculus -> medial geniculate -> layer 4 cortex in caudolateral pallium -> layers 2/3 -> layers 5/6 & CSt

Question 24

SUMMARY (1)

Answer 24

• sensory systems = much in common BUT alos important difs depending on physical nature of sensory info/prevalence/variation/distribution in natural environment
• sensory info has dif sources in environment & spatio-temporal characteristics = integral
• sensory systems evolved to preserve (ie. retina) or enable recovery (ie. cochlea) spatial aspects when info = captured by sensory receptors located either in 1 (ie. elaborate sensory organs)/various body parts; provides brain w/egocentric spatial reference framework anchoring other allocentric frameworks where they might be needed for dif beh execution

Question 25

SUMMARY (2)

Answer 25

- we find organised feature/action maps of specialised neurons across sensory organs/dif brain areas - in sensory systems (where they preserve spatial info as it reaches retina of eye) such organisation = retinotopy - where mapping = organised along spectral content (wavelength) of sounds = tonotopy - parallel pathways = frequently found across otherwise sequentially-organised hierarchical pathways/networks in brain - sensory pathways = well studied & understood aka. good egs for such brain organisation