1. 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 things (i.e. olfaction).

2. 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:
Syllables: Consist of the basic elements of song for a species. They develop and crystallize during song learning Some types of syllables
harmonic stacks
frequency sweeps
high-pitch notes
broadband sounds
Motifs: Consist of a number of introductory notes followed by sequences of syllables: these sequences are crystallized
Bouts: Consist of a sequence of motifs that is not necessarily stereotyped even in the adult
In adult birdsong, syllables may also be demarcated by intervals of relative silence or sharp frequency modulation changes

3. Zebra Finches female

4. Nuclei of the avian song learning and production pathways
Red: Anterior forebrain pathway
(learning pathway)
Blue: (production/output pathway)
cHV: Hyperstriatum Ventrale
NCM: Neostriatum Caudo-Medial nucleus
NCM
HVc: High Vocal Center (Hyperstriatum Ventralis pars caudalis)
NIf: interfacial nucleus of the neostriatum
MMAN: Medial nucleus Magnocelularis of the Anterior Neostriatum
RA: Robust nucleus of the Archistriatum
LMAN: Lateral Magnocellular nucleus of the Anterior Neostriatum
DLM: Dorso-Lateral division of the Medial thalamus
Uva: nucleus Uvaeformis of the thalamus
X: Area X of the paraolfactory lobe
nXII: nucleus of the 12th cranial nerve
DM: Dorso-Medial subdivision of the intercollicular nucleus
VL medulla: VentroLateral medulla
AVT: Area Ventralis of Tsai

5. Lateralization of birdsong production: Hypoglossal dominance
White crown sparrows chaffinches and canaries are left dominant
Severing the left hypoglossal nerve (XII cranial nerve) has a more profound effect on song production than severing of the right.
Zebra finches are right dominant.
Swamp sparrows show no lateralization

6. Lateralization of birdsong production: Hemispheric dominance
Lesion experiments of HVc: High Vocal Center (Hyperstriatum Ventralis pars caudalis) in canaries:
Left HVc lesions produce profound disruption of song production
Right HVc lesions have modest effects on song production
Lesioning effects on either side were largely reversible (recuperation takes months)
Requires auditory feedback.
Bilateral lesions of HVc produce permanent and profound loss of song production.

7. 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.
Cells in the…
LMAN Area X
RA nXIIts …
…accumulate testosterone or testosterone metabolites: these chemicals can directly influence cell proliferation (neurogenesis) and 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 (pair bonding)
Stress, diet parasite load
Season: light/dark cycles, temperature
Weather: barometric pressure, temperature

8. Hormone levels mediate sexually related differences in size of song production nuclei
Comparative analysis establishes that dimorphic singing is related to relative brain dimorphism

9. Hormones and neurogenesis: The development of new neurons
One limitation of most central nervous system neurons: Once development is complete, neurogenesis ends.
Notable exceptions in vertebrates:
bird song system which seasonally expand based on neurogenesis.
olfactory receptor cells which regularly turn over
GNRH cells in some fishes
Testosterone flux in songbirds appears to rekindle neurogenesis
Can result in as much as a doubling in structure size/cell count
True in males and females
Males either seasonally or by injections
Greatest effect in juvenile vs. adult males
Results in male song production out of season
Females by injection (but to a lesser extent than in males).
Injection of testosterone alone in females affects song production in some species but not others.
Thus in both males and females there is a direct correlation between:
Increased testosterone
Increased cell proliferation in LMAN, Area X, RA and nXIIts
Overall size of these areas
Increased number of syllables produced

10. Hormones and neurogenesis: The development of new neurons
Estrogen:
Developing male gonads produce estrogen
Blockade of estrogen during development in males results in loss of song production as adults.
Is not reversible with testosterone injections as adults
In females, estrogen injection during development followed by testosterone injection as adults results in song production.
Generally more effective than testosterone injections alone
This tells us that estrogen mediates the development of normal bird song centers in adults and testosterone regulates the expression of song in normal adults

11. Its not just neurogenesis: Gene expression in song in the zebra finch learning pathway
Experiment:
Hypothesis: learning is mediated in the caudal part of the neostriatum (NCM) and of the hyperstriatum ventrale (cHV).
Procedures:
Zebra finch males were reared without their father/song and exposed to a tape-recorded song during the sensory period for song learning.
Placed in sound isolation cages for sensory motor period. As sound production began recordings were made of the juvenile song to confirm learning from tutor.
At the start of the crystallization period, they were re-exposed to the tutor song but in the dark so that they would not sing.
Matched control experiments also used canary song.
Other controls received the same treatment but were not re-exposed to tutor song.
Measured expression of the protein products of the immediate early genes egr-1 (ZENK) and c-fos: these are indicators of neural activity

12. Results:
Only males exposed to within species tutor song showed increased staining for immediate early genes egr-1 (ZENK) and c-fos in the cell bodies of:
NCM
cHV
Males did not show increased ZENK or c-fos in any other conventional "song-production/learning nuclei.“
Subsequent studies show that even playback of different species song will not induce ZENK or c-fos
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.

13. Counts of stained cells reveal relative differences in ZENK & c-fos between experimental and controls
c-Fos
ZENK
experimental
control

14. 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
Stained nuclei per sq mm
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