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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:
- Two separate experiments were performed. The first experiment was a recapitulation of the classical
- song-specific adaptation experiment [Chew et al., 1995b]. 4 standard songs (with motifs of 4 or 5
- syllables each) were presented to the bird over 2 epochs. During the first epoch, each song was
- presented for 25 bouts of 5 motifs each, with inter-motif intervals of 30ms and inter-bout intervals
- of random length, uniformly distributed between 7 and 13 seconds. After each of the 4 songs was presented
- during the first epoch, songs were repeated (in the same order) during the second epoch, for 10 bouts each.
- The second experiment involved 4 distinct epochs, during which 1 standard song (consisting of 5 syllables)
- and 18 variations on that song were presented. The 18 variations were composed of (whole syllable versus
- intra-syllable perturbations), (per- turbations of syllable b, d or e), and (harmonic stack insertions,
- spectrally matched noise insertions, or silence insertions), for a total of (2 x 3 x 3 = 18) distinct
- perturba- tions. During the first epoch (baseline phase 1), each of the 19 different motifs (18 perturbed
- motifs plus 1 standard motif) were presented in a random order, 25 times each. Motifs were separated by a
- random inter-motif interval, uniformly distributed between 0.5 and 1.5 seconds. During the second epoch
- (oddball phase), 3-6 standard motifs (uniformly distributed) were followed by a single perturbed motif,
- with 30ms between motifs. There were 25 such trials for each of the 18 perturbed motifs. During the third
- epoch (habituation phase), the standard motif was presented in 80 bouts of 5 motifs each. Motifs were
- separated by 30ms, and bouts were separated by 2-4 seconds (uniformly distributed). The fourth and final
- epoch (baseline phase 2), was an exact repetition of the first epoch (baseline phase 1).
- AUDITORY STIMULATION:
- Auditory stimuli were synthesized using custom MATLAB code and stimulus com- ponents 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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