hi anders, the optimal set of stimulus parameters will depend somewhat on what cortical area(s) you are trying to map and on the details of your acquisition. in general, stimulating with both clockwise- and counterclockwise-rotating wedges for polar angle mapping and with both expanding and contracting rings for eccentricity mapping improves the accuracy of the maps, and the proper analysis of this data is implemented fsfast. the width of the wedge or the ring will depend on the cortical area you are trying to stimulate, but you may want to consider a thinner wedge. also, 8 Hz flickering has been shown to activate area V1 more strongly than other frequencies, and smoothly moving stimuli can also help. then, depending on your voxel size, field strength, coil array, etc., you could include more cycles and may need to average together multiple runs.
marty, roger et al. have a few nice papers that i'd recommend that discuss some of these details relating to phase-encoded retinotopic stimuli. Sereno & Tootell. Curr Opin Neurobiol. 2005;15(2):135-44. Tootell et al. J Neurosci. 1997;17(18):7060-78. Sereno et al. Science. 1995;268(5212):889-93. (the '97 paper discusses the ring/wedge thickness, the '95 paper discusses the advantages of using both expanding + contracting stimuli, and the '05 paper discusses the use of smoothly varying stimuli.) hope this helps. were you able to get reasonable looking maps with the stimuli you described below? -jon On Thu, 7 Jul 2011, Anders Hougaard wrote: > Dear freesurfers, > > > Which stimuli do you think provide the best retinotopic maps? > > I have done a retinotopy analysis using the following stimuli: > > Polar angle: > > - 45 deg counter-clockwise rotating wedge > - 8 unique positions > - flickering at 2 Hz > - stimulation period: 36 sec > - no. of cycles: 6 > - TR = 3 > > Eccentricity: > > - expanding ring > - 8 unique positions > - flickering at 2 Hz > - stimulation period: 36 sec > - no. of cycles: 6 > - TR = 3 > > Any suggestions on how to optimize this stimulation? > E.g. different period length, more runs, bi-directional, different TR > > Thank you! > > Best regards, > > Anders > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
