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Dear all,<br><br>I was looking at my lcmv-beamformer maps of ~200 Sec of <br>eyes closed resting state MEG activity and wondering if<br>what I was seeing is the center of sphere artefact.<br><br>The code I used is:<br><br>%filtering of the data<br>cfg = [];<br>cfg.bpfilter = 'yes';<br>cfg.bpfilttype = 'but';<br>cfg.bpfreq = [5 45];<br>cfg.bpfiltord = 4;<br>cfg.bpfiltdir = 'twopass';<br><br>[meg_data] = ft_preprocessing(cfg,meg_data);<br><br>%PCA to extract components with max explained variance<br>[cf,pcs,vexp] = princomp(meg_data.trial{1},'econ');<br>pexp = 100*vexp/sum(vexp);<br>indx = find(cumsum(vexp) <=90);<br>meg_data.trial{1} = (pcs(:,indx)*cv(:,indx)')';<br><br>% computing the covariance matrix<br>cfg = [];<br>cfg.channel = {'MEG'};<br>cfg.covariance = 'yes';<br>cfg.pad = 'maxperlen';<br>cfg.sgncmb = {'MEG' 'MEG'};<br>cfg.removemean = 'yes';<br><br>[cov_data] = ft_timelockanalysis(cfg,meg_data);<br><br>%LCMV beamformer<br>cfg = [];<br>cfg.channel = {'MEG'};<br>cfg.grid = grid_data;<br>cfg.vol = hdm;<br>cfg.method = 'lcmv';<br>cfg.grid.dim = [Nx Ny Nz];<br><br>cfg.lcmv.fixedori = 'no';<br>cfg.lcmv.lambda = '5%';<br>cfg.lcmv.projectnoise = 'yes';<br>cfg.lcmv.keepfilters = 'yes';<br>cfg.lcmv.projectmom = 'no';<br>cfg.lcmv.keepmom = 'no';<br>cfg.lcmv.reducerank = 2;<br>cfg.lcmv.normalize = 'yes';<br><br>[bf] = ft_sourceanalysis(cfg,cov_data);<br><br>%make power unit invariant<br>bf.avg.pow = bf.avg.pow./max(bf.avg.pow);<br><br>Since I don't have enough experience to judge about that<br>I wanted to ask if anybody out there with experience <br>could tell me their opinion.<br><br>The grid was computed using an inwardshift of -0.5 and a grid<br>resolution of 2.5 mm. The head model using the ft_prepare_singleshell.<br><br>Any help,advice, comments or suggestions would be highly appreciated.<br><br>Best,<br>Fred<br><br><br><br>-- <br>Frédéric Roux, PhD student<br>Department of Neurophysiology<br>Max Planck Institute for Brain Research<br>D-60529 Frankfurt am Main<br>Frederic.Roux@brain.mpg.de<br>+49(0)69630183225<br><br><br> </div></body>
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