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Hi Darren, Yes, you are absolutely right - if this is the network structure, you would indeed expect that the MAP estimates for the intrinsic connections S1<->S2, S1->T1 and S2->T2 are zero. Melinda, is this how your connectivity structure looks like? All the best Klaas At 00:15 19/06/2007, Darren G wrote: >Dear Melina > >I wonder about the structure of your DCM. I assume you have >driving, intrinsic and possibly >modulatory connections. From your description below you say the >DCM.A matrix values corresponding >to the sustained -> transient connections are 0, but I wonder if the >DCM.A values for the transient >network connections are 0. My guess is they are not. > >I am probably wrong but here is my suggestion: I wonder if you have >a situation in which you do not >actually propagate or connect your driving inputs into your >sustained network? As an example, see >below (I am ignoring modulatory inputs if any) T means a node in the >transient network and S in >the sustained network. > > > INPUT --> T1 <- S1 > | ^ > | | > v v > T2 <- S2 > >In this case the driving input enters at T1 which is connected to >T2, but S1 and S2 never see this >input since their connections are only backwards. I would expect >DCM.A(T1 > T2) to have some value, >but DCM.A(S1 > T1), DCM.A(S2 > T2) and DCM.A (S1 <> S2) would have >values of 0. > >As I said this may be incorrect and Klaas will correct me if this >would not be expected, but I hope >this helps. > >Darren > >==============Original message text=============== >On Mon, 18 Jun 2007 5:15:50 pm CDT Melina Uncapher wrote: > >Hi Klaas, > >Thanks for your reply. Unfortunately, I'd already checked all those points >and none appeared to be the culprit. The estimation appears normal, with >~10-12 steps, no error messages, manual specification, all data were in >their appropriate spots in the matrices, etc. Even changing the precision of >the printed values made no difference to the values. In fact, if I remove >other connections the values are estimated fine. Has this been encountered >in SPM5? > >Thanks, >~Melina > >***************************************** >Melina R. Uncapher, Ph.D. >Functional NeuroImaging of Memory Group >Center for the Neurobiology of Learning and Memory >Department of Neurobiology and Behavior >University of California at Irvine >http:[log in to unmask] > >-----Original Message----- >From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On >Behalf Of Klaas Enno Stephan >Sent: Monday, June 18, 2007 2:35 PM >To: [log in to unmask] >Subject: Re: [SPM] DCM parameter estimation problem > >Dear Melina, > >This sounds odd, and I am not sure what the problem could be. Here >are a few things that you may wish to check (unless you have already done >so): > >1. How many steps does the estimation take? Does it converge after a >single step? If so, have you double checked that you specified the >driving inputs correctly? Also, do you get any warnings or errors >messages during estimation? >2. Are you sure that the values in DCM.A are really zero, or not >just close to zero? You can check this by printing the values at >higher precision, using something like the sprintf command in Matlab. >3. Did you manually specify the DCM that you are trying to estimate, >or was it created algorithmically? If the latter, have you double >checked whether anything went wrong in transferring the timeseries, >i.e. does DCM.xY.u look like it contains your time series? > >This is all I can think of at the moment. You may also want to try >estimating the model with the code in SPM 5. Generally, I would >always recommend to use SPM 5 for DCM. The code is much more robust >than in SPM 2. > >Best wishes, >Klaas > > > >At 18:57 13/06/2007, you wrote: > >Hi Klaas, > > > >I'm a postdoc working with Mick Rugg in California, and I've an odd (and > >hopefully quick) DCM question for you. In running my fourth set of DCMs, >I'm > >running into a problem I've not encountered before. I'm looking at how > >regions that exhibit sustained activity interact with those showing > >transient activity, but when both sets of regions are included in the same > >model, the parameters in the A matrix corresponding to the connection > >strength from the sustained to the transient regions do not seem to get > >estimated. The DCM.a is appropriate, but the DCM.A contains 0s in the > >relevant cells (yet has appropriate values in the cells for the visual > >region to the transient regions). > > > >I should qualify this by stating I'm still using SPM2, as all my prior DCMs > >have been estimated in SPM2. I've tried to run diagnostics by >systematically > >excluding regions or otherwise changing the A matrix, yet I find no rhyme >or > >reason to when the parameters are estimated and when they're not. Have you > >encountered this before? > > > >Any help would be greatly appreciated. Mick sends his best. > > > >Thanks in advance, > >~Melina Uncapher > > > >***************************************** > >Melina R. Uncapher, Ph.D. > >Functional NeuroImaging of Memory Group > >Center for the Neurobiology of Learning and Memory > >Department of Neurobiology and Behavior > >University of California at Irvine > >http://fnim.bio.uci.edu>[log in to unmask] > > > > >===========End of original message text=========== > > > >-------------------------------- >Darren R. Gitelman, M.D. >Department of Neurology >710 N. Lake Shore Dr. #1122 >Chicago, IL 60611 >Voice: (312) 908-8614 >Fax: (312) 908-5073 >--------------------------------