Neural data processing

A single tungsten microelectrode with impedance about 1MΩ was used to record neuronal activity from a cockroach restrained firmly on a plastic disk. This plastic disk was located in a faraday cage to reduce the effects of electromagnetic interference. After an initial amplification using a preamplifier, analog neural data was amplified by the main amplifier with a gain of 2000 and band-passed filtered in the range of 0.3-3 kHz. The analog data were digitized using a National Instrument ADC card (30K samples/s). All procedures, including data acquisition and analyses, were controlled by a user-written program in the Labview environment (Version 8.6, National Instruments, USA). Recorded data was up-sampled (up-sampling factor= 2) to increase the number of data points and reduce the alignment error [15]. Using an automatic amplitude thresholding strategy, spikes were extracted. The labeling process for extracted spikes was performed by 3 experts. In the first stage two experts (1 neurologist and 1 neuroscientist) labeled the extracted spikes; however, to resolve any conflicts the third person (a neuroscientist) finalized the labeling procedure. There was 93% agreement between the first two experts.