Laboratory Amplifier / Audio System (LabAmp-02)

Description

TREC AC Main Amplifier (LabAmp-02) is a single-channel, differential main amplifier for neurophysiological applications (e.g. extracellular recording with microelectrodes). This Instrument is designed to work with high impedance metal microelectrodes and preamplifiers in research and teaching applications. Extracellular neurophysiological recordings with high impedance microelectrodes can easily be done from excitable tissues such as nerve and muscle. The Instrument is not intended for clinical measurements using human subjects. 

Figure 1: Differential input preamplifier DPA-4

The single channel of the LabAmp-02 contains a high-gain, low-noise differential amplifier stage followed by low frequency and high-frequency filters. The amplifier has two different filter amplifiers, a single unit activity (SUA) filter –amplifier and a local field potential (LFP) filter amplifier, both are connected parallel in the signal path. Record Mode offers two levels of signal gain (x10, x100) in a first stage and 4 additional levels (x5, x10, x25 and x50) in a final amplifier stage (see figure 2).

Each amplifier has different bandpass characteristics for single unit activity (SUA) 500Hz…20kHz and local field potentials (LFP) 0,1Hz…140Hz. An audio monitor and a window discriminator is integrated in the device. The window discriminator is an instrument for the separation of single neural spike trains from a multiunit recording containing more than one neural element. The window discriminator of the LabAmp-02 produces a window in amplitude. The window can be adjusted in height, above or below baseline. The trigger point is set by a continuously adjustable level control for either positive or negative slope detection. The signal and both window levels are multiplexed so that only one channel of the oscilloscope is necessary.

A reliable description of the activity pattern of a single, well-isolated neuron is the key to many important experiments in neurophysiology. Once the quality of the recorded signal has been optimized and enhanced by the proper microelectrodes, amplification, and bandpass filtering of the SUA-filter/amplifier module in the LabAmp-02, the yield is determined by the power and flexibility of the spike discrimination and processing system. The TREC modular signal conditioners have been optimized for this purpose.

Figure 2: Block diagram of the laboratory main amplifier LabAmp-02

The figure 2 shows the proper inter-connections for discrimination and visual on-line inspection of extracellular unit records. The multiplexed output of the window discriminator is viewed on one trace of an oscilloscope triggered by the threshold trigger output discriminator. Small bars in the multiplexed signal, indicating the precise upper and lower bounds of the discrimination, set by the user to coincide with the portion of the waveform most distinctive from others exceeding the trigger level.

The LabAmp-02 has an integrated audio monitor with loudspeaker. This unit provides audio reproduction of electrophysiological signals. The unit combines an audio amplifier in a compact, rugged package. This is especially suited to monitoring neural firing and muscle contractions. The audio monitor input is internally connected to the SUA-Filter amplifier output.

Table 1: Technical Data of the LabAmp-02