Subject Interface Stimulation

The Subject Interface Module (SIM) is the control object for the SI2, SI4, and SI8 devices. It connects to a DSP-M or optical QDSP card in your RZ processor. The Subject Interface is configurable with stimulator cards (IZV), analog amplifier cards (PZA), or digital headstage interface cards (PZD). Because of the diversity in functionality of this device, each card type has its own "Sub-HAL" object within Synapse that is used to configure those cards. The acquisition and stimulation all happen within the Sub-HALs, which are all independent objects in the Processing Tree.

Tip

See the Electrical Stimulation Guide for help with experiment design.

IZV Stimulator

The IZV can split the available boards into sub-stimulators which are completely isolated from one another. It is typically controlled by the Electrical Stim Driver gizmo.

IZV Block Diagram

IZV Options

IZV Stimulator Configure Tab Options

When using Sub Stimulators, each sub-stimulator must be configured independently. Each sub-stimulator has its own multi-channel input signal. For example, the first sub-stimulator uses the gizmo input called "VoiceIn-A", the second sub-stimulator uses "VoiceIn-B" gizmo input, and so on. It is generally expected that this signal comes from an Electrical Stim Driver gizmo so that it has the proper format. The format is a multi-channel signal where the odd channels contain the actual stim waveforms and the even channels contain the target stim channel. For an input that has 4 unique stim signals, it will be an 8-channel signal where channels 1, 3, 5, 7 are the stim signals and channels 2, 4, 6, 8 are the corresponding target stim channels.

Important

The sub stimulators must be ordered from highest to lowest bank count. For example, if you want a 2 bank stimulator and a 4 bank stimulator, then Sub Stimulator 1 should have 4 banks and Sub Stimulator 2 should have 2 banks.

Each physical IZV board has 4 unique hardware voices that can be routed to its 16 output channels.

The data table at the bottom shows the mapping between the gizmo input voices and the physical hardware voices. The first column is the voice of the "VoiceIn" for this sub-stimulator. The middle column is the board number within the sub- stimulator that it uses and the hardware voice on that board it uses (a, b, c, d). The last column is the range of channel numbers that the VoiceIn stim channels should address.

Check the Switching Headstage option only if you are using a ZC-SW switching headstage. If the electrode has a reference site, you may want to short reference to ground in the headstage to help with stimulation artifacts. See Using a Switching Headstage for more information.

Caution

The switching headstage only supports up to ±15 V per channel and can NOT be used in Serial Output Mode.

Option	Description
Output Type	Select whether this sub amp is current-controlled or voltage-controlled. AC Mode adds a DC block to the output signal (an in-line 20 MOhm resistor and 22 uF capacitor in parallel).
Output Mode	The settings in this group determine how the input VoiceIn signals are mapped to a particular hardware voice on a board of the sub-stimulator. It handles this channel mapping for you, so the stim channels you give it from the Electrical Stim Driver gizmo make sense for how the headstage is physically connected. Parallel assumes boards in this sub-stimulator are wired in parallel, so you can get more than 4 unique voices per 16 channels or up to 4 higher current voices per 16 channels. The VoiceIn input to the sub-stimulator must contain enough voices/channels. Serial assumes channel 16 on all sub-stimulator boards is physically shorted together. Allows one channel of bipolar stimulation with a higher compliance range. Repeated repeats the same input voices on all boards of the sub-stimulator.
Number of Boards	Number of boards in sub-stimulator
Current Doubling	None - all four hardware voices on each board are unique. By two - connect pairs of hardware voices together on each board to achieve 2x max current compliance. By four - connect all four hardware voices together on each board to achieve 4x max current compliance.
Voices per Board	How many unique stim signals for each stimulator board
Range per Board	How many channels are available to stim on each board

IZV Stimulator Compliance and Safety Tab Options

Option	Description
Safety Mode	If enabled, IZV checks total output current and will disarm if system is outside specs. The device requires arming before it will operate. To arm, run your experiment and make sure no stim presentation is sent to the device. The physical IZV card will light all LEDs red if it is not ready to be armed. It will like all LEDs green when it is ready to be armed. When armed, it will light the LEDs on the stimulation channels during stimulation.
Remote Arming	Enable this to force the user to arm the device via the SIM touchscreen interface. Otherwise, the user can arm the device via a button in Synapse at run-time.
Max Output Voltage	Set the maximum allowed output voltage for this sub-stimulator. Max is 15-18 V, depending on the current battery level. If Safety Mode is Enabled and any channel goes beyond 1 V of this maximum, a Fault occurs and disarms the device.
Grounding	Isolated - each bank of 16 uses its own ground connection for return path. Shared - all banks in sub-stimulator share the same ground return path (ground on first bank of sub-stimulator). To Banana Jack - connect sub-stimulator ground to the external banana jack on physical SIM device. Caution: When using multiple sub-stimulators make sure they aren't all sharing the External Ground connection or else they won't be isolated!
Monitoring	Off - disable compliance voltage monitoring. View Only - visualize the compliance voltage for each voice in the Flow Plot at runtime but do not save it to disk. Store - visualize and save the compliance voltage for each voice. The voltage data is scaled by 1000 and saved as 16-bit integers at the system sampling rate.
Impedance Check	Enable run-time impedance check
Save to CSV	Log impedance values into CSV file stored within the block folder whenever an impedance check runs

See the SIM section of the System 3 Manual for more information about configuring and using the IZV interface.

Runtime Interface

States of the IZV Runtime Interface

If Safety Mode is enabled on the Safety and Compliance Tab, then an LED will show the state of the compliance monitor. If Remote Arming is disabled, the Arm/Disarm button is shown and the device can be armed when ready.

The system can only Arm if the fiber is connected and a zero current command is sent to the SIM device, so make sure the gizmo controlling stimulation (typically an Electrical Stim Driver) is muted.

Impedance Checking

When Impedance Checking is enabled, a user interface appears at runtime.

IZV Impedance Checking Interface

The IZV tab provides an interface for impedance checking on all channels. The display represents the stimulation channels divided into banks of eight channels, broken up by sub-stimulator. Channel numbers are labeled above and below the bank column in the diagram.

In the area above the probe diagram, you can set test signal frequency and amplitude, and define the high and low impedance threshold targets for visualization below the diagram.

Running the Check

Run an impedance check on the selected sub-stimulator. The test signal (sine wave of frequency defined by Freq (Hz) parameter and amplitude defined by Target (uA) parameter) is presented iteratively on each channel in the currently selected sub-stimulator for 500 ms and the impedance is measured.

Check All. Run an impedance check for all channels on all sub-stimulators by cycling through each bank of channels using the test signal as described above.

Stop Checking. Stops the impedance checking prematurely.

Results of impedance check are indicated by color: below low impedance threshold (green), above high impedance threshold (red), between low and high impedance thresholds (yellow). The actual impedance values (in kOhm) are displayed beneath each indicator.

Double-click on an individual LED indicator to run the impedance check on just that channel.