Zebra Finch : The machine behind the mouth (or beak)
General facts about Zebra Finches:
•The common and widespread in Australia (particularly drier areas), Timor and the
Lesser Sunda Islands.
•Live year round in social flocks of up to 100 or more birds.
•Feed on grass seed and insects.
•One of the most common “caged birds” selectively bread for a number of traits.
•Considered to be one of the best model systems for basic biomedical research of
learning and memory.
•Also used as a model system to study many other thing (i.e. olfaction).
The syrinx: The song machine
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located at the point where the trachea branches into the two primary bronchi.
Sound is generated when:
Air from air sacs is forced through the bronchi & syrinx
the air molecules vibrate as they pass through the narrow passageways between the
external labia & the tympanic membrane.
Because there are 2 separate passageways and membranes, some birds are able to
generate multiple sounds (harmonics) at the same time:
Basic harmonic stack
clay-colored thrush
Zebra Finch Song : Unique because of its harmonic characteristics and complexity
The song of the zebra finch as of other birds can be broken down into 3 hierarchical levels:
1. Syllables: Consist of the basic elements of song for a species. They develop and crystallize
during song learning Some types of syllables
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harmonic stacks
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frequency sweeps
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high-pitch notes
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broadband sounds
2. Motifs: Consist of a number of introductory notes followed by sequences of syllables: these
sequences are crystallized
3. Bouts: Consist of a sequence of motifs that is not necessarily stereotyped even in the adult
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In adult birdsong, syllables may also be demarcated by intervals of relative silence or
sharp frequency modulation changes
Zebra Finches female
Zebra finch hearing
•The most sensitive hearing thresholds of zebra finches are still not quite
as good as those of humans.
•Zebra finches can discriminating among complex harmonic sounds such
as detecting the mistuning of a single harmonic in a harmonic stack.
Nuclei of the avian song learning and production pathways
Red (learning pathway)
Blue (production pathway) is the song output pathway
cHV: Hyperstriatum Ventrale
NCM: Neostriatum Caudo-Medial nucleus
HVc: High Vocal Center (Hyperstriatum Ventralis pars caudalis)
NIf: interfacial nucleus of the neostriatum
MMAN: Medial nucleus
Magnocelularis of the Anterior
Neostriatum
NCM
RA: Robust nucleus
of the Archistriatum
LMAN: Lateral Magnocellular
nucleus of the Anterior
Neostriatum
nXII: nucleus of the
12th cranial nerve
X: Area X of the paraolfactory lobe
DLM: Dorso-Lateral division
of the Medial thalamus
AVT: Area Ventralis of Tsai
VL medulla: VentroLateral medulla
Uva: nucleus Uvaeformis of the thalamus
DM: Dorso-Medial subdivision of the intercollicular nucleus
Hormones control brain structure size… controls acquisition/singing behavior
Learning and production systems also change size, complexity or protein profiles with
changing hormonal levels.
There is evidence that song production and learning are hormone-dependent.
EG:
Cells in the…
LMAN
RA
nXIIts …
…accumulate testosterone or testosterone metabolites: these chemicals can
directly influence cell proliferation: nuclei size
Male produced estrogen and melatonin are necessary for normal development of HVC--RA pathway.
Known environmental mediators of hormone levels:
•Social interactions: territorial battles, sex, child
bearing, love
•Stress, diet parasite load
•Season: light/dark cycles, temperature
•Weather: barometric pressure, temperature
Hormone levels mediate sexually related differences in song production nuclei
Experiment:
Localized neuronal activation in the zebra finch brain is related to the strength of song learning
Rational:
1. It is not known where in the brain the memories of these learned sounds are stored.
2. Song perception in songbirds may involve neuronal activation in brain regions that have not
traditionally been implicated in the control of song production or song learning.
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Hypothesis: learning is mediated in the caudal part of the neostriatum (NCM) and of the
hyperstriatum ventrale (cHV).
Procedures:
1. Zebra finch males (Taeniopygia guttata castanotis) were reared without their
father/song and exposed to a tape-recorded song during the sensitive period for
song learning.
2. Placed in sound isolation cages 76-142 days when sound production began
recordings were made of the juvenile song to confirm learning from tutor.
3. At 250 days (when song begins crystallization) adults, they were reexposed to
the tutor song but in the dark so that they would not sing.
4. Controls received all of the same treatment except they were not reexposed to
tutor song.
5. Measured expression of the protein products of the immediate early genes egr1 (ZENK) and c-fos: these are indicators of neural activity
Results:
The males showed increased staining for immediate early genes egr-1 (ZENK)
and c-fos in the cell bodies of:
1. NCM
2. cHV
Males did not show increased ZENK or c-fos in any other region. conventional
"song-control nuclei."
Photomicrographs of the zebra finch brain at the level of the NCM, showing egr-1 (ZENK)-like immunostaining. The
sections are from a bird in the control (a) and of a bird in the experimental group (b) that both showed a high degree of
song learning. V, ventricle; Hp, hippocampus.
Counts of stained cells reveal relative differences in ZENK & c-fos between
experimental and controls
c-Fos
ZENK
experimental
control
Stained nuclei per sq mm
Furthermore: Strength of ZENK and c-fos staining in NCM and cHV
correlates to the number of song elements that the birds had copied from the
tutor song
ZENK
C-fos
Fraction shared song elements
Exp
Exp
Cont.
Cont.
Conclusion: These results show localized neural activation in response to tutor
song exposure that correlates with the strength of song learning. This suggests
that the memory for tutor song is stored in NCM and cHV
Ultimate explanation for bird song: parasite resistance
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Females prefer males with higher quality song and higher quality plumage.
Healthy males in heavily parasitized species may result in extravagant trait expression (i.e. elaborate
song and fancy feathers.
Conclusion: parasite load influences phenotype which in turn influences mate choice decisions. Thus,
song complexity could be driven by parasite resistance.
Garamszegi et al. (2003)