Cyberamp 380

For mapping A1, stimulus-evoked local field potentials (LFPs) were recorded with a glass micropipette filled with 1 M NaCl (∼1 MΩ at 1 kHz). ABR and LFP recordings were filtered and amplified (1–1000 Hz, AI-401, CyberAmp 380; Axon Instruments), digitized, and stored on a computer (AxoGraph software). LFPs for CSD profiles were recorded using a 16-channel silicon multiprobe (∼2–3 MΩ at 1 kHz for each 177-μm² recording site, 100-μm separation between recording sites; NeuroNexus Technologies), filtered and amplified (1 Hz to 10 kHz, AI-405, CyberAmp 380), digitized and stored on a computer.

Recording sessions lasted 1-8 h, depending on the animal's response and vitality. Analog voltage was recorded at 10 kHz using two four-channel differential amplifiers (model 1700, AM systems, Carlsborg, WA, USA), a signal conditioner (cyberamp 380, Axon Instruments, Union City, CA, USA), and a 16 bit A-D converter (Digidata 1322A, Axon Instruments, Union City, CA, USA). The signal was recorded and played back in real time using Axoscope software (Molecular Device, Sunnyvale, CA, USA) and processed using DataView software (W.J. Heitler, University of St. Andrews, Scotland). Data were chosen for analysis based on two criteria: (i) recorded bouts showing simultaneous rhythmic activity [as defined in Pearson and Iles (1970) (link)] in at least two hemiganglia, for at least five cycles; and (ii) instantaneous frequencies calculated between bursts recorded in the two nerves had to be consistent throughout the entire recording bout (variation <25%). Bursts were only included if they comprised four spikes or more, and were terminated at spike i, when: f (i) <10 Hz, or when: f (i+1)

Animals were implanted under anesthesia with 1.5% isoflurane in 100% oxygen an electrode of nickel-chromium (140 microns) in prefrontal cortex (1.5 mm rostral, 1.5 mm lateral and 1 mm ventral to bregma), a second electrode in the CA1 region of hippocampus (-2.4 mm rostral, 1.5 mm lateral, 1.5 mm ventral), two stainless steel screws in the pre-frontal region, for ground and indifferent references, and a silver plate in the muscles of the neck for emg recording. Recovery took place in their cage in a sound attenuated chamber under 12:12h ld regime with a light intensity of 95 Lux and 0 Lux during the darkness phase, constant temperature 22–24°C and ad libitum access to food and water. Nine days after surgery, mice were transferred to a circular cage and the implanted cap fixed to a rotating anti-gravitational connector allowing free movements; ld regime was not changed (see S1 Fig). After a period of habituation of 72 h, 24 h of uninterrupted recording were acquired. eeg of the cortex, hippocampus and emg signals were filtered from 0.5 Hz to 200 Hz, amplified (x5000-10,000) (Cyberamp 380, Axon Instruments) and digitized at 1 kHz (Axon CNS Digidata 1440).

The IC LFP was amplified (10k gain) and filtered (from 1 to 2 kHz bandpass filter) by a signal conditioner (Cyberamp 380, Axon Instruments). The reference soundtrack was also recorded on a different channel (same filters but no amplification) to obtain the exact time of the sound stimuli. Data were sampled at 10 kHz for both channels using an A/D converter (National Instruments Inc., mod NIDAQ 6023E) and stored on a computer hard disk for offline analyses.