Howdy-

Well, 3dNetCorr is not built for that per se. One typically enters an ROI map and a 4D time series dataset in the same space, and then the program calculates the average time series in each ROI, and makes a correlation matrix out of that (with extra functionality like doing Fisher Z transform if you want, as well as being able to calculate whole brain correlation maps for each average ROI time series, and probably some other things I am forgetting...). It is certainly possible to select subsets/intervals of a time series for calculating the correlations, but...

... I don't know that it is practical to calculate the correlation of just specific event responses (or, depending on the study design, even if it is possible). Firstly, most event related responses are quite short: by definition, event-related designs have a very short stimulus, and the actual blood response time will be probably be something like 8-15 s long in total (depending on what kind of hemodynamic response is appropriate for modeling). For the TR used in most FMRI studies, that would be something in the range of 2-7 time points, and calculating correlation between that few time points is not meaningful (the uncertainty would be sooo large, and it would likely be dominated by noise). Event related HRFs tend to be quite noisy (which is why people tend to have many repeated events in a stimulus paradigm, for improved statistics). I would think that a single HRF would be pretty meaningless to correlate, purely due to the noise present (FMRI is very noisy). Finally, in most event-related designs I have seen, there is expected overlap of HRFs due to stimuli-- that is, the events are *not* typically spaced far enough apart to have a brain response start and finish before another event has started.

Another consideration, even if you want to take the whole time series (not just one stimulus) and make correlation matrices: often, event-related designs have randomized timings across subjects, so I am not sure if calculating correlation matrices to compare across subjects would be meaningful.

Please let me know your thoughts about these thoughts.

--pt