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NPB162-L7

3 min read

📗 -> 01/28/25: NPB162-L7

[Lecture Slide Link]

🎤 Vocab

❗ Unit and Larger Context

All of these notes are specific to the Barn Owl, not necessarily humans

✒️ -> Scratch Notes

Interaural Timing Difference (ITD)

Interaural Intensity Difference (IID)

In barn owls, Posterior Lemniscal Nucleus

  • In human, the equivalent is Lateral Superior Olive (LSO)
  • Its where IID is computed
  • Received excitatory input from the contralateral angular nucleus (NA, +) and inhibitory input from the contralateral posterior lateral lemniscal nucleus (itself on the other side)
  • Ratio of excitation/inhibition determines the IID

Left sound - High activity in right LLDp
Center - Zero activity in right LLDp
Right Sound - Zero activity in right LLDp

Inferior Colliculus (Spatial Map)

Inferior colliculus is divided into three main regions

  • ICC core: core of the central nucleus of the IC
  • ICX: IC external nucleus of the IC
  • ICCIs: Lateral shell of the central nucleus of the IC

ICC core

Receives input from the contralateral laminar nucleus (timing)
The ICC core presents a tonotopic organization on one axis and an ITD topographic organization on the perpendicular axis.
Individual neurons present ITD tuning with phase ambiguous responses.

  • No IID/ILD, but sharp frequency tuning

Lateral shell of the central nucleus (ICCIs?)

  • Most neurons respond to IID and ITD
  • Phase ambiguity is still present
    • Is the ITD really the same, or is it just a perfect phase shift?

External Nucleus of IC (ICX)

Phase ambiguity is not present in ICX. This is the result of convergence of multiple inputs from ICCls with similar (but not identical) frequency preference but with same ITD tuning. This improves ITD tuning but widens frequency tuning curves.

  • The first center that eliminates ambiguity

  • Topographic space map (one of the 1 things discovered about Owls?)

  • Neurons are space-specific, only respond to natural sound coming from a well-defined region of real-world space

  • Respond well to sounds in space, according to topographic space map. ICX neurons were robust against:

    • Intensity
    • Clicks, noises, and tone bursts
    • High-frequency of owl’s audible range (5-8.7 kHz)

  • Both the time difference and intensity difference must fall within the range to which the neuron is tuned for (ITD and ILD tuning must be specific to the neuron)

Optic Tectum: An auditory-visual map

  • Similar to our (humans) superior colliculus, but ours don’t receive as much visual input

  • The optic tectum is the homologous of the mammalian superior colliculus.

  • Neurons in this area respond to both auditory and visual stimuli arising from the same area in space.

Plasticity in the Optic Tectum: Prism Experiments

  • Site of plasticity for the adaptation seems to be the ICX

  • Develop 2 different maps of the world, if they develop the maps young enough and practice they can switch between them (like a prism world and normal world)

    • Used as a model for switching between languages for bilinguals
    • Also used as an example of plasticity as adults, and as kids. Adults not able to adapt to prism glasses as well.
      • They wouldn’t shift unless they were given a reward - given the chance to hunt they saw adaption (compared to just flashing lights)

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