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Constant Current or Voltage Linear Isolated Stimulator

The Constant Current and Constant Voltage Isolated Linear Stimulator (STMISOLA) will connect to any analog output signal drive (±10 V input) and provides considerable flexibility in stimulation protocols:

Voltage and current stimulator (unipolar or bipolar)—the STMISOLA connects directly to the STM100C (50 output port) or the UIM100C (Analog Output 0 or 1 port) associated with the MP1X0 system. The STMISOLA can also connect directly to an MP36.

Linear stimulatorthe STMISOLA can be used to generate stimulation signals that can have arbitrary waveshape. Typically, stimulators can only generate simple unipolar or bipolar pulses. The STMISOLA, however, can output unipolar or bipolar arbitrary waves such as pulse (single or train), square, sine, triangle, exponentially decaying, modulated envelopes, and fully user-specified types.

The STMISOLA can output either voltage or current waveforms.

        Voltage (V) mode—the STMISOLA multiplies the Control Input Voltage by a factor of 20, to present that amplified signal at the STMISOLA output.

            In the case of a maximum ±10 V Control Input Voltage, the STMISOLA will output a ±200 V signal, with an output impedance of either 100 ohms or 1 K ohms. These output impedance settings will act to limit the available output current.

        Current (I) mode—two settings:

        The STMISOLA provides two options for output current mode.

    1. High current mode (Zout switch set to 100 ohms), provides a gain factor of 10 ma/volt.
    2. Low current mode (Zout switch set to 1 K ohms), provides a gain factor of 1 ma/volt. Low current mode permits much improved control for currents less than 10ma.

The STMISOLA multiplies the Control Voltage by the factor indicated (K in ma/V) to present that associated output current at the STMISOLA output.

In the case of a maximum ±10 V Control Input Voltage, for:

Zout = 100 ohms, K=10 ma/V:  the STMISOLA will output ±100 ma

Zout = 100 ohms, K=1 ma/V:  the STMISOLA will output ±10 ma

In both cases, the voltage compliance is ±200 V.

Isolation characteristicsThe STMISOLA isolates the Control Input Voltage signal from the stimulus output to 1500 VDC HiPot and approximately 1000 pF of coupling capacitance.

This very high degree of input/output isolation helps ensure subject safety and helps considerably to substantially reduce, or eliminate, stimulus artifact.

Stimulus artifact results when some percentage of electrical current from the stimulation site is directed to the recording site due to electrical leakage paths intrinsic to the stimulation/recording equipment. In the case of the STMISOLA, the leakage conductance and capacitance that permit this artifact to occur are reduced to very small values.

Power ON SafetyWhen you Power ON the STMISOLA, you must also hold Reset for at least 3 seconds. This forces the unit into an "operational but no output state" and protects the subject if accidentally connected to electrodes on power up.

IMPORTANT Comprehensive Safety Guidelines for Performing Electrical Stimulation on Subjects: read Application Note 257 - Safe Use of Electrical Stimulators

The STMISOLA is well-suited for transcranial direct current stimulation (tDCS or HD-tDCS), a form of neuro-stimulation which employs the use of low level (typically under 2 ma) constant, unipolar, direct current. The STMISOLA will support arbitrarily long, constant, non-varying, direct output currents, so long as the associated voltage compliance is 100 VDC or less. The tDCS level is adjusted by holding a stable voltage to the control voltage input of the STMISOLA. The control voltage can be set in AcqKnowledge, to be output to STMISOLA via MP150 analog output.

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MP Systems Hardware Guide
AcqKnowledge 4 Software Guide
MP Research System User List
AcqKnowledge 3.9 Software Guide
Application Note: tDCS with STMISOLA
Reference Article - The Relationship between Energy, Phase Charge, Impedance, and Perceived Sensation in Electrotactile Stimulation
MP Research Catalog
BioNomadix Wireless Physiology Catalog
New Products Catalog
MRI Catalog
VR and Stimulus Presentation Catalog
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