Bird Song & hearing

746 - Lecture 1

Aim Outline the physiology of hearing and

vocalisations seasonal variation developmental processes the way this leads to dialects

hearing in owls role in prey capture

Birdsong What is a sonogram?

time on x axis; frequency on y axis intensity shown by colour / black

intensity/time

sonogram

time

freq

uenc

y

Birdsong Each species has its own song

Dialects White-crowned sparrow

Isolated from sound juveniles hear no sound will sing in

spring

Play song to juveniles (I)

Played another species song only Record next spring song

Play song to juveniles (II)

Summary so far Dialects in many passerines Juveniles learn father’s song

Prefer own species song develop their own

Next: how is this achieved in brain?

Song brain map

controls song

only in song birds

auditory inputto area L

Brainstem (bilateral coordination)

During singing need

HVc RA

HVc activity precedes song by 50ms

Stimulate HVc and disrupt singing

Stimulate RA and disrupt singing

HVc can generate pattern on own

During learning forebrain essential

LMAN X

LMAN carries “jitter” needed in learning process

HVc neuron - own song

intensity

sonogram

total count of spikes

spike replicates

HVc neuron-synthetic song

intensity

sonogram

total count of spikes

spike replicates

Another synthetic song

intensity

sonogram

total count of spikes

Summary of HVc expt HVc is sensitive

to own song selective

During singing network via UVA &

NIF acts a delay produces efference

copy comparison with

acoustic input Check that birds is

singing “correctly”

Seasonality Canaries add/replace syllables annually HVc grows/shrinks annually

new neurons! testosterone causes

more growth in males singing in females and

castrati

Summary so far Bird song is complex behaviour Many songs learnt

initial learning as juvenile used as adult

HVc controls motor output responds to song pattern possible site of song learning

Major impacts: Neurons added to brain Focused nuclei affected during

learning Male and female radically different

Owl hearing Problem

locate mouse 1) how far away 2) which direction

implies ability to locate mouse in x,y coordinates

Going ... Total darkness Infra-red picture

Behaviour Method

elevation

azimuth

mount high frequency coil on head in magnetic field

Results Error less than 5o

for most angles

Owl ears are hidden behind facial ruff

Owl ears are asymmetric

Left up Right down

Sound at the 2 ears has:

Time difference gets to further away

ear later ITD

Intensity difference quieter in auditory

shadow IID

How so accurate? both ears contribute to L/R and U/D

Neurons respond... only to one point in space

count of spikes to sound

2-d tonotopic map

Map generated from ? IID

intensity coded by spikes; summate at synapse

ITD Jeffress hypothesis:

axon conduction delay leads to coincidence

Jeffress hypothesis

N. laminaris

Time delay coincidence detection

Pathways

IID pathway: orange

ITD pathway: blue

Local anaesthetic used to show separate pathways

Summary Asymmetry of ears allows

ITD IID

Separation of intensity and time delay in CNS allows tonotopic map align to visual cortex

Catch mouse