Triggerring 2 MEAs simultaneously

Dear MCS users,

I am trying to run 2 MEAs simultaneously in a two-pathway LTP experiment. I attempted to use the SynchOut signal from one of the STGs and feed it into "Trigger In" socket of the other STG. However, while the first signal from SynchOut starts the other STG, the second signal effectively shuts the other STG down. So it acts like an alternating "1" and "0" signal for the triggerred STG.

My stimulation protocols are identical for both STGs as follows:

First line (first signal):
Channel 1: -60 uA; 40uS; 60 uA; 40 us; 0 uA; 24920 uS
Channel 2: 0 uA; 40uS; 0 uA; 40 us; 0 uA; 24920 uS

Second line (second signal):
Channel 1: 0 uA; 40uS; 0 uA; 40 us; 0 uA; 24920 uS
Channel 2: -60 uA; 40uS; 60 uA; 40 us; 0 uA; 24920 uS

SynchOut pulses are always set to:
first line 1; 40 uS; 1; 40 uS; 0; 24920 uS
second line 1; 40 uS; 1; 40 uS; 0; 24920 uS


When using just one MEA, I get alternating activation of control pathway (channel 1) and test pathway (channel 2) every 25 s with the above protocol.

Could the reason for sequential "1" and "0" signals be in the fact that the value of the TTL pulse is dependent on the value of the amplitude of the Channel 1 pulse? It alternates between -60 and 0.

I was able to solve the problem partially. Having uploaded identical continuous stimulation protocols to both STGs, I would start STG1, which in turn triggerred STG2. I would then disconnect the BNC cable from the STG2 trigger-in socket before the second ("0") signal arrives from the STG1. In this case, STG2 would run seemingly normally repeating the alternating activation pattern of the STG1. However, I still had to specify a trigger for MC Rack recording and display. As STG1 and STG2 are effectively disconnected, the trigger signal would come from only one of STG. I tried both Analog input or stimulus artefact-based trigger. As it turned out that in the MEA that did not supply the signal for the Display/Recording trigger, the stimulation time point slowly drifted away from trigger time "0".
In other words, despite both STGs were initially triggerred exactly simultaneously, their subsequent generation of signals was slightly asynchronous. The drift was about 1 ms in app. 5 min, which is probably not much. Hovewer that means that Analyzer ROI, measuring EPSP amplitude has to be constantly shifted for the "drifting" MEA. It is not possible during the recording and since LTP experiments are quite long, even 1 ms in 5 min is much.

Could you please suggest the way out of this situation? I am sorry for a lengthy description, but I tried to be as detailed as possible.

Many thanks,

Max

Dear Max

The jitter of the two internal clocks of the two STGs is only 3*10 E-6, which is quite small and cannot be further improved, though I understand that it is a problem for your current setup with two separate STG1002s.

I hope we understood your experiment correctly: You have two stimulating electrodes each on two MEAs, and use an alternating stimulus protocol on all four electrodes, right?

I believe the problem can be solved if you use the Sync Out outputs of both STGs, connect each to an analog input (A1 and A2, for instance), and implement two Trigger Detectors in MC_Rack, one based on A1 and the other on A2. You can then add two Analyzers triggered by STG 1 and 2 in your virtual rack, and analyze the parameters of both MEAs separately.

As an alternative to disconnecting the two STG from each other after the start, you could also build a small box with a switch and connect that to both trigger inputs to remote control both STGs simultaneously. On page 37 of the current version of the STG 1000 series user manual, you will find a suggested circuit diagram for building such a switch.

Does that solve the problem? Please ask if you have any additional questions.

Best regards, Christine (MCS)

Dear Christine,

Thank you for your prompt reply! As for the option 1, that you suggest, there still will be a problem with the Recorder. I usually record raw EPSPs and analyze them after replay, i.e. I do not save parameter date in the file. It seems that you suggest to record the EPSP measurements from the "lagging" MEA in the file which is OK, but the actual EPSP traces will be shifted further and further in the Display window because of the increasing jitter.

I have a question about the external trigger (option 2). Won't it do the same thing, what my SynchOut pulse does, i.e. switch the other STG on and off all the time? I would really appreciate the option of triggerring several (ideally 4) MEAs simultaneously for both channels. Can it be done with a Digital Output?

Thank you for your patience and care!

Max

Dear Max,

>Thank you for your prompt reply! As for the option 1, that
>you suggest, there still will be a problem with the
>Recorder. I usually record raw EPSPs and analyze them after
>replay, i.e. I do not save parameter date in the file. It
>seems that you suggest to record the EPSP measurements from
>the "lagging" MEA in the file which is OK, but the actual
>EPSP traces will be shifted further and further in the
>Display window because of the increasing jitter.

I meant that you could analyze both MEAs separately, that is, base the Analyzer 1 for MEA 1 on the Sync Out of STG 1 and the Analyzer 2 for MEA 2 on the Sync Out of STG 2. Then, the jitter would not matter, because each Analyzer is triggered separately by the internal clocks of the STGs. You could do this either online or offline afterwards.
For recording, you could select a longer window time, so that the jitter does not matter. Or will this increase your file size too much?

A perhaps more elegant way would be to use the digital port as the trigger input. In this case, you could configure the Trigger Detector such that if the Sync Out of STG 1 OR STG 2 is active, the recording sweep is started. A 3 BNC input slot for the digital input channel is available as an accessory. The options are explained in the MC_Rack Help under More Details > Trigger Detector. Please ask if something remains unclear.

>I have a question about the external trigger (option 2).
>Won't it do the same thing, what my SynchOut pulse does,
>i.e. switch the other STG on and off all the time?

No, my intention was that you activate this switch just once at the beginning of the stimulation, to start both STGs via the trigger inputs of the STG. This has the advantage, that you do not need to use the Sync Out output of one STG for triggering the second. You have then both Sync Outs free for triggering the MC_Card, and you would not have to disconnect the STGs manually after the start.

In summary, the ideal setup for two STGS in my opinion would be: A custom switch for starting both STGs, connected to Trig In of both STGs. Sync Out 1 connected to bit 0 of the digital port, Sync Out 2 connected to bit 1 of the digital port. The trigger detector based on the digital input channel with the settings "> both bits LOW", meaning
that the trigger is active if either STG 1 or 2 is active. I hope that I understood your application correctly. This is only a suggestion, of course, you would not need the digital port for the triggering. Everything would be a bit easier if you had a 4-channel STG :-)

>really appreciate the option of triggerring several (ideally
>4) MEAs simultaneously for both channels. Can it be done
>with a Digital Output?

Sorry, I am not quite sure what you mean. Do you mean triggering of the stimulation or the recording? What's exactly the question?

I hope this information is helpful for you. Please ask if something remains unclear.

Best regards, Christine

Dear Max

>really appreciate the option of triggerring several (ideally
>4) MEAs simultaneously for both channels. Can it be done
>with a Digital Output?

I just had another thought, maybe you meant that, too. You could use the digital output of the MC_Card for triggering both STGs:
You connect two digital output bits of the MC_Card with the two Trigger IN inputs of the STGs. A digital in/out extension with 16 BNC connectors for the inputs and 16 BNC connectors for the outputs is available as an accessory.
You then define an internal trigger with the trigger detector in your rack, time based at time = 0. You then trigger the Digital Output with this internal trigger.
So, when you start your rack, the STGs are started automatically. You then can use the Sync Outs of the STGs to trigger the MC_Card for data acquisition as suggested in my previous posting.

Best regards, Christine

Hi, Christine!

In your last posting, you described exactly the configuration I meant. I apologise for my vague English. As you probably guessed it is not my native language :-). How can I get a quote about the digital in/out extension with 16 BNC connectors?

Also, we do have an STG 1004 with 4 output channels, which I could use shortly. However, how should I configure the MC Stim software? At present, I use MC Stim 2.0.6. for STG 1002 and I upload the protocols to two different STGs 1002 via MEA Select. I noted you have MC Stim II v. 1.0.1.0 on the website. Would it work with STG 1004?

Thank you very much for your help!

Max

Dear Christine,

I just checked our 4-channel amplifier: it has 4 digital trigger-in and outputs and a USB connection to PC. However on the front panel it is called STG 1004. Its serial number is STG 1004 4056. I wonder if it isn't the STG 2004 after all?...I shall address this question to MCS support team also.

Many thanks for your assistance!

Max

Dear Max

The STG you are speaking of is an upgraded version to STG 2004. This instrument gives you a lot of flexibility in your protocols and triggering. The MC_Stimulus II program is the graphical user interface for controlling the 2000 series of STGs. You can use your old protocols from the MC_Stimulus program. You simply combine the two protocols for controlling the two STG 1002 to one file (you could do that by copy paste).

A new MC_Stimulus II version will be released soon, with nice new features. Please check whether you have registered to our mailing list, so that you will be informed of the free software upgrade. If not, you can register on the following page.

http://www.mcs-download.com/contact/contact.htm

You can get a quote for all MCS stuff from your local retailer. Please see the Sales Info on the web site.

http://www.mcs-download.com/salesinfo/distributors.htm

Best regards, Christine