Frequency Out of Range + Low Frequency Stimulation

The CereStim will claim its minimum frequency as 4 Hz, but there are many cases in which it will not allow the user to deliver a 4 Hz stimulation because the maximum value that can be held in memory is too long to get to that low of a frequency. It is dependent on the length of the stimulation segments and interphase.

A method of bypassing this issue will be detailed at the bottom of the article.

The formula for calculating frequency is:

f = Frequency

Tp = Time period

Time period can be defined as:

The formula for calculating these values is below:

PW1 - Phase width 1

IPD - Interphase delay

PW2 - Phase width 2

IPI - Interpulse Interval*

*Note: Interpulse interval is not defined by the customer directly. This value is determined when the customer inputs values for all of the other variables in the equation:

 

The maximum value that the IPI variable can be is 65535μS (Same maximum value as phase width and interpulse delay). To calculate the lowest possible frequency possible with your waveform parameters, we assume the IPI is set to its maximum value:

Phase Width 1 (PW1) + Interphase Delay (IPD) + Phase Width 2 (PW2) + 65535μS = Max Single Period 
1/Max Single Period = Lowest Frequency Possible 

If you input a low frequency value that would make the IPI exceed its maximum value of 65535μS, you will encounter an error message stating something to the effect of, "Frequency out of range". If you are set on a particular frequency, you will need to change one of the other waveform parameters (PW1, IPD, PW2) to make this possible.

Waveform parameter limitations

Phase width, interphase delay, and interpulse delay minimum values are limited by hardware. The Cerestim requires a fixed period of time to receive and implement instructions (ex. setting waveform parameters). The minimum values imposed for the aforementioned parameters are designed around this consideration. The maximum values for these parameters are limited by the Cerestim's memory.

Low frequency stimulation

It is possible to stimulate on the CereStim with a pulse frequency below 4 Hz with the methods below:

Trigger mode

In Stimmex (CereStim Matlab API) or in StimManager (CereStim GUI), you can set your CereStim to Trigger mode. This will set the Trigger BNC port on the front of the CereStim to look for a TTL high signal (Square wave must have voltage greater than 3.0 V to register as TTL high). Once triggered, the stimulation sequence set in either the API or the GUI will be executed with a latency of 1 μS +-0.1 μS between trigger being received and stimulation output. Send in a low frequency TTL pulse that matches the desired stimulation pulse frequency to achieve the sub 4hz goal.

Matlab Loop

You can break out your stimulation sequence in Matlab to a signal waveform and have it loop X number of times to achieve the desire stimulation pulse frequency. For example, instead of defining a waveform to execute with a frequency to 10 Hz, define the waveform to play once followed by a wait period, then loop the waveform with an if statement. It's worth noting that the latency of Matlab code execution will introduce slight levels of jitter latency into the stimulation (~a few milliseconds).

• Related Articles

• BOSS Was Unable to Start Correctly 0xc0150002

  This error indicates that the PC is missing Microsoft Visual C++ Service Pack 1 2005. You can download it here: http://www.microsoft.com/download/en/details.aspx?id=26347  If you would like to read more about this error, you can below: ...

• Fast Settle Functionality

  Stimulus delivery to recording electrodes or electrodes adjacent to the recording electrodes is likely to cause saturation with stimulation artifacts. Fast settle works to mitigate this, generally providing a shorter recovery from stimulation by ...

• NSP Gets Stuck in Initializing Step 2

  There is a known bug with NSPs with PNs 7530, 9650, and 10411 where their LCD screen shows "Initializing Step 2" and it gets stuck. This is a known issue associated with the NSPIF board (i.e. the PCI board that the fiber optic cable attaches to) that ...

• Noise Troubleshooting

  Introduction Noise troubleshooting is often times seen as an art that is full of unintuitive steps, confusing patterns, and maybe a little bit of magic. The truth is, getting rid of noise can be made to be a scientific and procedural process. The ...

• NEV and NSx File Specifications

  See the attached PDF for the current file specifications. Below you'll find a screenshot of our short summaries for the currently available file specifications in Central 7.0.6: