AOPI: Pulse Burst Train

The Pulse Burst Train Analog Output Plug-In (AOPI) enables you to generate a pulse pattern: A simple single pulse, a burst of pulses, or even a train of bursts of pulses.

Below we'll explain the individual parameters to set up the plug-in (see image right). This is followed by a few examples to illustrate the use.

• Plug-in parameters:
• Train
• Burst
• Pulse
• How to select a suitable update rate
• Examples:
• Single pulse
• Conditioning burst followed by a single test stimulus (superimposition)

Note: The choice of Update Rate in the general D/A parameters is very important to achieve correct timing of pulses.

The use of the Class and Active controls is equivalent to other plug-ins, The same goes for all general buttons.

Plug-in parameters

Parameters are divided into three groups:

• Train: Defines the train of bursts
• Burst: Defines the burst of pulses
• Pulse: Defines the individual pulse(s)

Let's start by defining the pulse(s).

Pulse parameters

Pulses are defined by these two parameters:

• Amplitude: The amplitude - or height - of the pulse. For negative-going pulses set Amplitude to a negative value.
• Pulse Width: The width of the pulse in seconds.

All pulses in a burst are identical: They have the same amplitude and pulse width. To achieve different amplitudes and/or pulse widths you must superimpose the output of two plug-ins.

Offset is solely controlled via the general parameters of the individual analog output channels.

Burst parameters

A burst is a series of pulses.

The burst can be defined in two equivalent ways depending on the position of the center switch - either (top position):

• Nmb Pulses: The number of pulses in a burst. To achieve a single pulse set Nmb Pulses (as well as Nmb Bursts below) to one
• Pulse Interval: The time interval from the onset of one pulse to the onset of the next. Time interval measured in seconds.

Or (switch in bottom position):

• Burst Length: The duration of the burst measured in seconds: Nmb Pulses * Pulse Interval
• Pulse Freq: Pulse frequency in Hz: 1 / Pulse Interval

Whatever set of parameters you choose to enter, the other set will automatically be calculated and displayed for your information.

Train parameters

A train is a series of bursts. The train may be delayed relative to the analog output trigger - this is set via the Delay control, measured in seconds.

The train can be defined in two equivalent ways depending on the position of the center switch - either (top position):

• Nmb Bursts: The number of bursts in a train. To achieve a single pulse set Nmb Bursts (as well as Nmb Pulses above) to one
• Burst Interval: The time interval in seconds from the onset of one burst to the onset of the next.

Or (switch in bottom position):

• Train Length: The duration of the train in seconds: Nmb Bursts * Burst Interval
• Burst Freq: Burst frequency in Hz: 1 / Burst Interval

Whatever set of parameters you choose to enter, the other set will automatically be calculated and displayed for your information.

How to select a suitable update rate

The analog output is updated at a fixed rate, which is set via the general D/A parameters, Update Rate. This update rate also specifies the time resolution of the analog output, and therefore the precision in timing of pulses in this plug-in.

Here are a few hints on how to select an update rate - update interval in seconds is the reciprocal of the update rate in Hz, Tupd = 1/Fupd:

• Pulse width must be an integer multiple of the update interval, i.e. a pulse width of 1 ms requires an update rate of at least 1 kHz (Tupd=1 ms; 2, 3 or 4 kHz will do as well).
• Also the pulse interval minus the pulse width (the pulse-off period, Toff) must be an integer multiple of the update interval, i.e. a pulse frequency of 20 Hz (pulse interval 50 ms) and pulse width of 1 ms requires that (50 - 1) = 49 ms is a multible of Tupd; a 1 kHz update rate is still OK.
• The update rate must be a multiple of the burst frequency as well. The factor depends on the number of pulses in a burst, etc. A burst frequency of 3 Hz, a pulse frequency of 20 Hz and a pulse width of 1 ms can be achieved with an update rate of e.g. 3 kHz (neither e.g. 300 Hz nor 1.5 kHz would be sufficient to produce the pulse width of 1 ms).

In order to keep the work load on the computer low, a low - but sufficient - update rate is recommended. Some single burst examples of optimal update rates follow:

It's a good idea to check the timing of pulses with an oscilloscope. If timing is not as you expect, please check all settings incl. the update rate.

Also the amplitude of pulses can be checked with an oscilloscope. Don't forget, that the analog output is scaled by the sensitivity of the individual analog output channel as well as it may be offset. The voltage resolution of most MIO-boards is 20 V / 4096 = 4.88 mV.

Examples

A few Examples to illustrate the use of this plug-in: One very simple and one advanced…

Single pulse

In order to generate only a single pulse for each sweep, first set both Nmb. Bursts in Train and Nmb Pulses in Burst to one.

Then set Active, Delay, Amplitude and Pulse Width to suit your purpose.

Repeat this for each defined class, or use the Edit All feature. The Active parameter is pt. not available through Edit All.

Conditioning burst followed by a single test stimulus

Assume you want a conditioning burst of stimuli pulses followed by a single test stimulus from the same stimulator. The test stimulus may require other characteristics than the conditioning stimuli:
In this example we'll go for a burst of five electrical stimuli with an amplitude of 0.8x some threshold and applied at a 20 Hz rate. These stimuli should be 0.2 ms wide and followed by a single stimulus 500 ms after burst onset with an amplitude of 1.5x the threshold, 1 ms wide.

This is possible only if the stimulator can be controlled by an analog signal. The NoxiStim-stimulator supports this.

This set-up involves superimposition of two plug-ins: One to generate the conditioning burst and one to generate the single test pulse. Choosing the First AO Channel set Active to Superimpose.

For the SMI-stimulator in analog ext. scaled mode a +10 V input will result in a stimulus current equal to the amplitude value set on the stimulators front panel. I.e. setting Sensitivity to 100E-3 V allows you to set pulse amplitudes in the range 0-100% of the stimulators setting - which in this example should be adjusted to 1.5x threshold.

To achieve a 0.2 ms wide pulse in the burst, the Update Rate must be at least 5 kHz, which is fine for all other demands in this example.

Conditioning burst of stimuli

Load the AOPI Pulse Burst Train for the Primary PlugIn 1, and configure it as follows (assuming no classification):

The burst should start immediately so Delay will be zero. Only one burst is applied per sweep so Nmb. Bursts will be one - other Train parameters are irrelevant.

In the Burst section first set Pulse Freq to 20 Hz or Pulse Interval to 0.050 s. Then set Nmb. Pulses to five.

Pulse Amplitude will be 0.8/1.5x100=53.33 % (as we set the 1.5x to match 100 %). Pulse Width is 0.0002 s.

Single test stimulus

Load the AOPI Pulse Burst Train for the Secondary PlugIn 1, and configure it as follows (still assuming no classification):

The single test stimulus should be delivered 500 ms after the onset of the conditioning burst: Set Delay to 0.500 s. Nmb. Bursts will be one - other train parameters are irrelevant.

In the Burst section set Nmb. Pulses to one - other parameters are irrelevant.

Pulse Amplitude will be 100.00 % and Pulse Width 0.0010 s.

Classification

Classification may be used to vary e.g. the time interval between conditioning and test (Delay parameter in the single test stimulus set-up), and/or test stimulus amplitude (Amplitude in the single test stimulus set-up).