Contributions:CereStim

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Versioning

Blackrock CereStim 96.

Author

Alexander Belsten (belsten@neurotechcenter.org)

Version History

  • 2021/07/21 - R6337 - Initial private release for internal testing.

Source Code Revisions

  • Initial development: 6337
  • Known to compile under: 6340
  • Broken since: --

Functional Description

This output extension integrates the Blackrock CereStim 96 intracranial stimulator with BCI2000. This integration enables automated stimulation of up to 96 electrodes with 15 different stimulation waveforms.

Integration into BCI2000

To enable the use of the CereStim with BCI2000, first enable the extension in your CMake configuration in the Extensions folder of the CMake GUI (enable EXTENSIONS_CERESTIM=On). Then generate the BCI2000 Visual Studio solution in CMake (More details about this can be found on the Configuring BCI2000 for Compilation page). Next, open the solution with Visual Studio and rebuild the BCI2000FrameworkAppModule. Then rebuild any user application module with which you want to use the extension. Once the extension is built into the user application, you can enable it by appending --EnableCereStim=1 to the user application module start executable command in your batch file.

Parameters

The CereStim is configured in the "CereStim" tab. The configurable parameters are:

AppliedVoltage

The CereStim drives current, so the applied voltage fluctuates according to the impedance between the current source (electrode) and drain. This dropdown parameter sets the maximum applied voltage. Note that there will be no notification that this maximum has been met.

AppliedCurrent

This parameter sets the maximum applied current in microamps. Unlike the maximum applied voltage, which fluctuates and therefore may or may not hit the maximum, maximum applied current parameter serves as a safety check for your uploaded stimulation configurations. Setting this parameter to a desired maximum applied current ensures that no stimulation above this current will be applied. If set to auto, the default will be the maximum current at which the CereStim can stimulate.

AppliedPhaseCharge

This parameter sets the maximum applied phase charge, where charge=amplitude*width. Amplitude is the current amplitude in microamps, and width is phase duration in microseconds. If set to auto, this parameter will default to the maximum value.

AppliedFrequency

This parameter sets the maximum frequency that stimulation pulses can have in Hz. If set to auto, this value defaults to the maximum.

StimulationConfigurations

This parameter is where stimulation pulses are defined. You can define up to 15 different stimulation pulses. The pulse shapes are defined according to Fig. 1. For each configuration, if the Cathode first row is 1, then the positive magnitude pulse precedes the negative pulse. If this row is 0, then the negative pulse precedes the positive pulse. The current sink for each pulse is the patient ground, which is the green safety connector on the back of the CereStim. However, suppose you wish to provide bipolar stimulation between two different electrodes within the brain. In that case, you can make two configurations that have the same pulse shape parameters but have reversed Cathode first parameters. These stimulation configurations can be triggered at the same time to approximate a bipolar stimulation pattern. Current can still potentially flow to the patient ground, but if the impedance between the two electrodes is significantly less than the impedance between the electrodes and patient ground, the majority of the current will flow between the two electrodes. Information on how to define these two electrodes can be found in the StimulationTriggers parameter. Note that valid frequencies depend on the phase and interphase duration of the pulse.

StimulationTriggers

This parameter defines when electrodes are stimulated, with what configuration they are stimulated with, and what electrodes are stimulated. The Expression row defines when electrodes are stimulated by specifying a BCI2000 expression. When this expression evaluates true, the electrodes will be stimulated with the pulse shape defined in the Configuration ID row. Note that two columns can have the same Expression, which allows for concurrent stimulation between different electrode locations. The Configuration ID defines the applied pulse shape and corresponds to the column number in the StimulationConfiguration parameter. Lastly, the Electrode(s) row specifies which electrodes will be stimulated. Elements in this row can be single values that specify a single electrode, or an embedded list in which you can specify multiple electrodes (from 1-96).

Note: You can only stimulate up to 15 electrodes concurrently. Concurrent stimulation groups, as defined by their equivalent Expression expression, must also have non-overlapping electrode lists.

DeviceInfo

This parameter is auto-populated with information about the hardware and firmware versions of the CereStim stimulator that is connected. This information will be viewable during offline analysis by opening the resulting .dat file.

States

CereStimStimulation

This binary state is equal to 1 when stimulation is being applied.

Latency

Figure 4: Latency of stimulation is about 17.3ms on average.

Figure 4 shows the latency of stimulation over 220 trials. Stimulation pulses were acquired using a gUSBamp at 38.4kHz and a block size of 50ms.

See also