Rp2.1 real time processor

Recordings were performed in a sound-attenuating chamber (Type 400, Industrial Acoustic Company, North Aurora, IL, USA) with the animal stabilized in a custom-made stereotaxic apparatus positioned on a vibration-isolated table. Animal’s temperature was kept at 37°C with a feedback-controlled heating pad. Acoustic stimuli were digitally generated using custom-written Matlab functions (version 7.5, The MathWorks Inc, Natick, MA, USA, RRID:SCR_001622). The stimuli were transferred to a D/A converter (RP2.1 real-time processor, 97.7 kHz sampling rate, Tucker-Davis Technologies, Alachua, FL, USA) and delivered through custom-made earphones (acoustic transducer: DT 770 pro, Beyer Dynamics) fitted with plastic tubes (length 35 mm, diameter 5 mm) which were positioned in the outer ear canal ~4 mm in front of the eardrum.

ABRs were collected within one week before electrophysiological recording experiments. Rats were anesthetized with ketamine (100 mg/kg) and xylazine (3 mg/kg) and placed in a sound-attenuated chamber. White noise bursts and pure tone pips, both of 5-ms duration, were delivered through an electrostatic speaker (ES1, Tucker Davis Technologies) placed 2.5 cm from the right ear. ABRs were recorded with two subdermal recording electrodes, one placed above the vertex of the skull, one placed behind the right pinna, and one subdermal ground electrode placed at the base of the tail. The electrodes were connected to a 2400A extracellular preamplifier and headstage (Dagan Corporation), or a RA16PA preamplifier and collected on an RP2.1 real-time processor (Tucker Davis Technologies). Signals were digitized and averaged across 512 trials, and bandpassed between 50 and 3000 Hz. ABR thresholds were estimated as the lowest sound level producing a peak in the signal at 3–5 ms following the sound onset.

Acoustic stimuli were digitally synthesized and controlled with custom software and delivered through an open-field speaker (FF-1 with SA1 amplifier and RP2.1 Real Time-Processor; Tucker-Davis Technologies) positioned ∼3 cm in front of the left ear. For calibration [sound pressure level (SPL), in dB re: 20 μPa] a microphone (model 4939 and Nexus amplifier; Bruel and Kjaer) was positioned in place of the animal at the tip of the left earbar. For mapping A1, tones were 100 ms in duration with 5-ms linear rise and fall ramps (range 5–40 kHz and 0–70 dB SPL). For determining ABR threshold, white-noise stimuli (10 ms duration, 3 ms rise/fall ramps) were delivered at 2/s for 100 repetitions and repeated at 0–70 dB SPL. For multiprobe recordings, 10 ms tones (3 ms rise/fall ramps) were delivered at 2, 5, 10, 20, and 40 Hz for 1 s trials in sets of 25 trials at 30 dB above threshold.