The Plexon Stimulator 2.0 is an electrically isolated 16-channel stimulator system with 16 individually programmable constant current sources that share a common return path. Stimulation currents can be defined with 16-bit precision up to ±1 mA and delivered with ±10 V compliance.
The graphical user interface makes it easy to generate bi-phasic rectangular pulses and bursts of pulses repeated at specific rates. In addition, arbitrary waveforms can easily be defined within text files and downloaded to the Stimulator 2.0.The Plexon Stimulator 2.0 delivers stimulation current with microAmp precision and microsecond temporal accuracy.
Stimulator User Interface
The actual current and voltage delivered to any electrode can be conveniently monitored on an oscilloscope using the standard BNC monitor outputs. Note: in order to maintain electrical isolation it is recommended to use an electrically isolated oscilloscope, such as a Tektronics TPS series scope.
Freely programmable waveforms
The stimulator can deliver arbitrary stimulation waveforms. The waveform current values are first defined within a text file and then downloaded to the Plexon Stimulator via the software interface. In this way, biological signals recorded by data acquisition systems or curves derived from mathematical functions can be used as stimulation waveforms. Stimulation pulses can be grouped and looped to generate pulse trains with arbitrary intra- and inter-burst intervals. Different waveform patterns and protocols can be applied to each of the 16 stimulation outputs. Stimulation protocols can be repeated as many times as desired, and then stopped either manually or on a trigger event. The internal 1 MHz clock guarantees precise timing across channels and over time.
Triggering stimulation
Every stimulation pattern can be started and stopped either manually, within the GUI, or with an external digital trigger (TTL). The Plexon stimulator allows you to trigger each of the 16 analog output channels independently. Complex stimulation patterns can be delivered in this way with precise timing based on different triggers. Each channel has a dedicated digital input that may be used in an edge triggered or level triggered (gated) mode to initiate stimulation with microsecond latency. Each channel also has a dedicated digital output to signal to other devices the precise time when stimulation is occurring.
Impedance Testing
The Plexon stimulator v2.0 can function either as a stimulator or as an electrode impedance tester.
In impedance testing mode, the stimulation pattern is a predefined 1 kHz ±100 nA sine wave that is automatically loaded into every channel. Playback of the impedance test waveform on particular channels is initiated from the GUI. The voltage elicited in response to the impedance test current is then observed on the voltage monitor output to determine the electrode impedance. Variable gain steps are provided to resolve a wide range of electrode impedances. To calculate the impedance of the electrode, multiply the peak to peak amplitude observed on the voltage monitor by the Vmon scaling factor.
In a typical experimental situation, the properties of the electrode may not be well known and may vary over time. Characterizing the electrode in saline prior to using it in vivo can provide valuable information about the condition of the electrode. For example, measuring the impedance of the electrode before and after implantation can help determine if the electrode was physically damaged during the implantation process. Likewise estimating the impedance, access resistance, and capacitance of the electrode periodically can provide clues as to the stability of the electrode tissue interface over time.
