Dear Mishna, There can be various approaches to selecting timeseries for your DCM such that they are well-standardised across subjects. The fundamental requirement is that across subjects timeseries are chosen such that they reflect the same experimental effect or functional profile (as assessed, for example, by an initial GM). That is, the same contrast at the same threshold should be chosen for selecting timeseries in each individual subject. Often, however, you will want to add additional anatomical constraints. For example, you could take the maximum from the group GLM and use this as a starting point for identifying the strongest local maximum, within each subject, that is located within a radius of X millimetres around the group maximum and that is located within the same anatomically defined structure (e.g. a particular gyrus or sulcus). You can finesse this approach by using probabilistic atlases, e.g. the SPM Anatomy Toolbox. The paper by Heim et al. that Qing mentioned in her previous e-mail has adopted that approach. You can also have a look at Stephan et al. 2007, J Neurosci, where this approach is described in full detail in the supplementary materials. See http://www.jneurosci.org/cgi/content/full/27/13/3512 Best wishes, Klaas ----- Ursprüngliche Mail ---- Von: Qing CAI <[log in to unmask]> An: [log in to unmask] Gesendet: Freitag, den 25. April 2008, 09:48:26 Uhr Betreff: Re: [SPM] Selecting VOIs for DCM Group analysis Dear Mina, I'm not DCM expert but before you get anwers from experts I think this paper could be helpful to answer your questions. Heim S, Eickhoff SB, Ischebeck AK, Friederici AD, Stephan KE, Amunts K (2007) Effective connectivity of the left BA 44, BA 45, and inferior temporal gyrus during lexical and phonological decisions identified with DCM. Hum Brain Mapp. http://www.ncbi.nlm.nih.gov/pubmed/18095285?dopt=Citation Best, Qing Mina Khoshnejad a écrit : > Hello, > > For group analysis in DCM, do we have to select VOI, for each subject > and each run seperately (according to the GLM results for each run)? > It takes a long time to do that, and also there is always variations > across subjects and not all subjects show the excat same pattern. so > the VOI might vary a bit from subject to subject. > > What is the general approach to select VOI for a group DCM? > > Many thanks for your answer in advance. > Mina > > > ------------------------------------------------------------------------ > Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try > it now. > <http://us.rd.yahoo.com/evt=51733/*http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ%20> __________________________________________________________ Gesendet von Yahoo! Mail. Mehr Möglichkeiten, in Kontakt zu bleiben. http://de.overview.mail.yahoo.com