Map recording system

We recorded multi-unit (MUA) and single-unit (SUA) activity from ventral area V4 (81 MUA, 19 SUA), the thalamic pulvinar (dorsal pulvinar: 102 MUA, 34 SUA; ventral pulvinar: 108 MUA, 12 SUA) and the LGN (89 MUA, 16 SUA) in two adult Rhesus macaques (Macaca mulatta, monkey E and B). Data were recorded during a total of 113 recording sessions (62 monkey E, 51 monkey B) with 4 to 8 microelectrodes simultaneously (Thomas Recording GmbH, Giessen, Germany). Of those sessions, 95 recordings (49 monkey E, 46 monkey B) contained sites that met our inclusion criteria (uninterrupted recordings without drifts, a minimum number of 10 identical trials as well as a minimum mean firing rate of 5 spikes/s) and were considered for analysis. Spiking activity was collected with the MAP recording system (Plexon Inc., Dallas TX, USA). Spike candidates were identified online through RASPUTIN software (Plexon Inc., Dallas TX, USA) on a PC receiving the digitized signals. Waveform thresholds were manually adjusted for each channel before the start of data acquisition. After the experiment, units were isolated in PCA space in the commercially available “Offline Sorter” (Plexon Inc., Dallas TX, USA) and time stamps were saved for further analysis.

During each training session, electrocorticograms (ECoG) and local field potentials (LFP) were recorded with a MAP recording system (Plexon Inc., Dallax, TX, USA) to which the animals were connected via a movable tether. ECoG and field potentials were filtered between 0.7 and 300 Hz and digitized at 1 kHz. Auditory stimuli were generated in MATLAB (Mathworks, Natick, TX, USA) and presented inside the chamber with an audio amplifier and electrostatic speaker (SRM313 and modified SR-307, Stax Ltd., Japan; average free-field sound pressure level amounted to 75 dB). The frequency response of the speaker was flat +/− 3 dB between 0.5 and 2 kHz.

Recordings were performed in a test chamber that was identical to the home-cage. Data were recorded at 40 Khz using a Multichannel Acquisition Processor (MAP) recording system (Plexon, Dallas, TX, USA), as described earlier.^{28 (link)} A 750-μs data sample was stored whenever the signal crossed a preset voltage threshold. Data were clustered and analyzed offline (see below).