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- These experiments were conducted as follows...
- SUBJECTS:
- Electrophysiological recordings were carried out in 6 adult zebra finches (Taeniopygia guttata) from the
- MIT zebra finch breeding facility. Birds ranged from 120-400 days post-hatch in age.
- Craniotomies were performed and headposts implanted on birds in order to prepare birds
- for head-fixation and electrophysiological recordings.
- HEAD FIXATION AND E-PHYS RECORDINGS:
- In advance of recording, birds were gradually habituated to the recording setup over the course of 3 days.
- Neuropixel probes (Phase 3a [Jun et al., 2017]) were used together with OpenEphys software
- (https://open-ephys.org/) for data acquisition, aloing with the PXIe system (National Instrument
- NI-PXIe-1071). Extracellular signals were amplified and filtered (0.3-10 kHz) to obtain action potential
- data. Craniotomies were made so that the center of the cranial aperture was centered above NCM (see
- surgery protocol), and the probe was lowered approximately 2000 𝜇m below the surface of the brain, until
- auditory responses were visible up to the 200th contact from the bottom of the probe (approximately
- 1500 𝜇m from the probe tip).
- Experiments took place on an optical table, surrounded by a home-made sound- reduction enclosure.
- EXPERIMENTAL STRUCTURE:
- This experiment involved 3 distinct songs presented in 2 distinct epochs. The songs each consisted
- of 5 syllables, and were repeated in bouts of 5 repetitions each. During the first epoch, the bouts
- are all separated by a standard inter-bout interval (called 𝜏0). This was 100ms for the first song,
- 1000ms for the second song, and 10000ms for the third song. This standard inter-bout interval was
- presented for 25 bouts. During the second epoch, inter-bout intervals were randomly chosen to be
- between 0.5 and 1.5 times 𝜏0, uniformly distributed. The experiment was performed so that each both
- epochs were completed with the first song before the second song was played. Then, both epochs were
- completed with the second song before the third song was played.
- AUDITORY STIMULATION:
- Auditory stimuli were synthesized using custom MATLAB code and stimulus components from the
- Tchernikovskii lab zebra finch song archive [Tchernichovski et al., 2004],
- http://ofer.sci.ccny.cuny.edu/songs. Perturbations were introduced by inserting harmonic stacks
- (in the case of harmonic stack substitution), eliminating all sound (in the case of silence
- substitutions), or inserting spectrally matched noise (in the case of noise substitution). All
- substitutions were made using cosine-squared ramps to minimize edge artifacts. Spectrally-matched
- noise was generated by randomizing the phase of the standard, unperturbed birdsong. Sound amplitudes
- were matched so that substitutions (aside from silence) were as loud as the standard song piece that
- they replaced.
- Sounds were played through a PyleDriverPro speaker, with SPL of 75 dB at 20 cm. This intensity was
- matched to the sound level of an adult zebra finch singing at the same distance.
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