How are inputs made into motion? We analyze feedback systems in auditory systems in birds.

Motivation

Birds are very good at producing and reproducing songs by moving their vocal cords complexly (sensory motor learning). Birds and Humans do not have much of a common ancestry (last one was fishes). 71% of the birds, both female and male birds sing, for Zebra finch it is a mating behaviour, so only male sing.

Zebra Finches

Zebra Finch’s Song

Both Zebra Finch and humans cannot learn to sing or speak anymore if in the critical period you don’t have a tutor, or somebody that speaks to you. Birds sing naturally (other neuroscientists using mices, they need to train them to do something specific). Scientists have analyzed the development of Zebra Finch singing as they aged using its spectogram, and have seen after some months it has become quite similar to the Tutor’s song.

  • Introductory note
  • Motif (repeated in the same way over and over again)
    • It has some syllables with gaps in between.

Zebra Finch’s necessary conditions

If a bird doesn’t have a tutor they don’t learn to sing properly (not stereotyped, and produce also different kinds of songs), they also need auditory feedback (if they cannot hear feedback, they cannot learn properly, e.g. if you make them deaf).

Isolated tutors on offsprings

Offsprings of isolated tutors are able to relearn after 3-4 generations the Zebra Finch stereotyped song.

Song Learning Theory

Serial Tutoring Paradigm

How can you elaborate a measure of vocal performance error, with respect for its semantics? For example if a baby is trying to say water, but says baba, how can you define such a measure? This measure should also work for birds.

This is where Serial Tutoring comes into place. Birds learn to do it in steps (as they need to learn both transitions source to target and target to source):

Learning singing patterns

Birdsong and Song System-20250327150309146 In nature, we can find animals that learn in steps and then compose these steps to express their final behavior.

In the image, you see a species of bird (Zebra Finch) that sings in regular patterns.
Suppose that initially, it knows how to sing in the pattern ABCABC, and you want to teach it ACBACB.
What happens is that it first learns to sing AC, then CB, and once it can perform BA, it is able to learn to sing ACBACB.

What can they learn

Juveniles match each syllable to the most spectrally similar sound in the target, regardless of its temporal position, resulting in unnecessary sequence errors, that they later try to correct (Lipkind et al. 2017)

They can learn sequence errors. They can also learn to correct pitch errors. They do not refurcate syllables (cannot learn b+ or b- but only one, but can add it into the song, they add the other into the call).

This is a Quadratic assignment problem, which is NP-hard (how they learn first, pitch or sequence error?). If you teach a sequence error and pitch error, the bird will:

  • first learn to change pitch match
  • Then change the position of the syllable.
  • Pitch assignment is greedy (they choose the version that is closer)
    • Every sillable greedily goes to the closest solution.

Learning in adults

  • They try to compensate the error also in adults (they can learn to change it) (little headphones on birds).
  • You can make them learn using trial and error (using small annoying sounds if they are too low for example). (you can make them further and further away from the correct pitch)
    • Also learn for visual feedback, but it is a different direction, they seem to like the light to be off, difference between deaf and hearing birds (these ones do not like the light to be off).
  • They learn from some sort of performance error.

Brain structures in song learning

Structures of Learning

Birds have more neurons per weight (about 2.2 times per unit weight). They recorded neural firing signals during song production, they see some kinds of clustering (in young birds it is quite random, while for adult birds they get more structured, and stereotyped). The following images are from a section called RA neurons. Birdsong and Song System-20250327153454452

Song Pathways

Using systems we studied in The Neuron (glass with thing). Some neurons spike at some specific points in time. Birdsong and Song System-20250328151813932 HVC neurons spike only once (tells you when to play the note), while RA multiple times in a sequence (Tells you the note). If you remove HVC they cannot sing anymore, the subsong is the same, but plastic song is different and also the adult song is different.

Thermal Cooling of HVC

HVC is for stereotypy and producing the songs. If you cool a brain area, you slow down the processes in that area. They observed that by cooling the HVC structure:

  • The song gets longer.
  • Then they sing faster if you remove the cooling and you just learn with the cooling part. This insight has been used in human speech articulation and timing (motor area for speak -> not well comprensible, broca area -> Speak slower).

LMAN circuits in the Bird

LMAN generates variability of the learnt songs. They lesioned LMAN to have this observation.

  • Prevent context-dependent changes to song variability.

  • If you deaf it, the song becomes degraded.

  • If you lesion LMAN before deafness, the song is the same (no plasticity in learned songs).

  • LMAN biases output to avoid punishment: if you deactivate it, it unlearns the just learned thing.

If you lesion Area X, even adult birds cannot learn anymore.

VTA pathway

VTA is a dopaminergic region that projects to Area X, if birds hear the sound the dopamine is lower (worse vs better than expected), if it doesn’t happen then it is a little higher suggesting internal rewards.

Forward models and prediction errors

The motor system is attempting to predict its sensory feedbacks: Birdsong and Song System-20250328153359503

References

[1] Lipkind et al. “Songbirds Work around Computational Complexity by Learning Song Vocabulary Independently of Sequence” Vol. 8(1), pp. 1247 2017