Why do my BOLD signals end up being the same even I change initial conditions?

[Şiyar Bahadır]

Hey everyone!

I am a surgeon working with TVB to find out a clinical use case. I thought I might try using surface stimulation to target Anterior Cingulate part of cortex trhough some inhibitory signals from different sites that are "surgically more accesible".

So I ran a connectivity analysis on another software (DSI Studio) and selected three surface targets to stimulate and watch the effects. I picked a frontal, temporal and parietal node and pairs and a triplet of these nodes to try and stimulated all sites with a sinusoidal wave.

I run my simulation for 2000 ms and the BOLD signal I get at the end is identical. 

What is the problem with my simulations?

See the screenshots below. 

[WOODMAN Michael]

Hi,

A 2s second simulation is too short a simulation to see a difference with the BOLD monitor, because of its low temporal resolution.  I would suggest first trying this with a 10 second simulation, and using a temporal average monitor first.  You will still be able to visualize the results on the anatomy but without the temporal smoothing of the BOLD monitor.

cheers,

Marmaduke

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[Şiyar Bahadır]

Hi Marmaduke,

Thank you very much for your answer. I just tried what you told and ran a 20 sec simulation with a temporal average monitor. The stimulus sites and the stimulus properties havent changed, but they again converge into the same response. Where there is almost zero change in most of the cortex, and a significant decrease in activation in cingulum. please see the attachments, the images are from around 8 sec mark and the pattern persists at 20 seconds.

So I thought maybe I did a great job picking where to stimulate and that's why it gives me these results, and tried with another parietal stimulus site which do not seem to be overly connected with cingulate cortex, but the results are the same. 

Is there something about my stimulus settings? Am I sending a very high frequency signal that somehow causes the entire system to collapse into a single result? 

Have a great day!

[WOODMAN Michael]

Hi,

Thanks for the screen shots.  Looking back at your model settings, I suspect the value of a=-2.0 for the oscillator is too damped, and d=0.02 results in a relatively slow fluctuation (alpha frequency if I recall correctly).  I would suggest looking at the model with the phase plane tool to adapt the parameters, particularly, increasing both a and d, using the Heun stochastic integrator in the phase plane, you should be able to identify where you get fluctuations which occur easily and on the time scale of interest.   The user guide briefly describes how this page works here

https://docs.thevirtualbrain.org/manuals/UserGuide/UserGuide-UI_Simulator.html#phase-plane

cheers,

Marmaduke

To view this discussion on the web visit https://groups.google.com/d/msgid/tvb-users/24b19d0c-f45e-4814-a532-01fe504cc789n%40googlegroups.com.
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