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On Nov 26, 2007, at 1:51 PM, [log in to unmask] wrote: > > > Hi Vince, > > To answer your question, I do have a temporal regressor design > that corresponds to the spike locations, but I have not used it in > GIFT to do a temporal sort. Is the temporal sort a feature in one > of the GIFT menus that I am unaware of? I can tell you that at > each interictal spike identified on the EEG, a canonical > hemodynamice response function model was implemented as a model for > the HR following an interictal spike. In the results that I sifted > through, one component clearly stands out (the one I sent) > regarding the spatial locations of activation I am expecting. > However, the corresponding time course is showing BOLD signal > decreases at the appropriate times, not increases. I am puzzled by > this. Any advice would be helpful. > > Thank you. > > Todd Penney > > Quoting Vince Calhoun <[log in to unmask]>: > >> Hi Todd, >> It's hard to tell the sign without seeing your model for spikes. >> Have you tried creating a regressor that corresponds to the spikes >> and use >> this to perform a temporal sort in GIFT? Joe, to answer your >> comment, the >> sign/factor score is reflected in the time course that is >> plotted. Seeing >> both the timecourse and the image give you the sign in the >> original data. >> >> Regards, >> >> Vince >> >> P.s. This might be best addressed if you e-mail the GIFT listserv >> ([log in to unmask]). >> >>> -----Original Message----- >>> From: SPM (Statistical Parametric Mapping) >>> [mailto:[log in to unmask]] On Behalf Of Dien, Joseph >>> Sent: Friday, November 23, 2007 7:07 PM >>> To: [log in to unmask] >>> Subject: Re: [SPM] independent component analysis of fMRI data >>> >>> I'm having a little trouble decoding the images due to issues >>> with the labeling on the scales but one possibility is that >>> the sign of an activation (or a factor score if using PCA >>> terminology) is arbitrary. The only thing that has a >>> meaningful relationship to the original data is the product >>> of the loading times the activation (factor score). Are the >>> loadings at the voxels of interest positive or negative? >>> >>> Cheers! >>> >>> Joe >>> >>> -----Original Message----- >>> From: SPM (Statistical Parametric Mapping) on behalf of Todd Penney >>> Sent: Fri 11/23/2007 12:55 PM >>> To: [log in to unmask] >>> Subject: [SPM] independent component analysis of fMRI data >>> >>> >>> >>> Hello all, >>> >>> I have a question regarding some ICA results I received on >>> a series >>> of fMRI images from an epileptic patient who underwent a continuous >>> EEG-fMRI scan. The patient was scanned for interictal epileptiform >>> activity that occurred on her EEG. >>> >>> I performed spatial ICA and found one component that I am >>> convinced >>> is related to the interictal epileptic spikes. The timing of >>> the BOLD >>> response corresponds to that of the epileptic spikes and the >>> activations are occurring in what looks like the temporal lobe (the >>> patient was diagnosed with right temporal lobe epilepsy). However, >>> the activations have a positive z-score but the BOLD response is >>> showing a DECREASE at each of the spike locations in the >>> spatial brain >>> maps (shown by the large signal discharges in the attached images). >>> This is puzzling to me as I am expecting a BOLD signal increase and >>> positive spatial weights. I have attached two .jpg files >>> showing the >>> brain maps of the component. Is it possible that perhaps the BOLD >>> signals are INCREASING because of the sign ambiguity when doing ICA >>> and that the spatial weights should be DEACTIVATIONS with the same >>> z-scores (which means all I have to do is multiply the time >>> course and >>> spatial weights by negative 1)? If not, how is it that I am getting >>> positive spatial weights with a declining BOLD response at >>> each spike? >>> These results are output from the GIFT ICA program. >>> >>> Thank you. >>> >>> Todd Penney >> >> > > ------------------------------------------------------------------------ -------- Joseph Dien Assistant Professor of Psychology Department of Psychology 419 Fraser Hall (by the coke machine) 1415 Jayhawk Blvd University of Kansas Lawrence, KS 66045-7556 E-mail: [log in to unmask] Office: 785-864-9822 (note: no voicemail) Fax: 785-864-5696 http://people.ku.edu/~jdien/Dien.html