Retinotopy Stimuli

(This page contains tips for creating retinotopy stimuli)

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 in 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. Depending on your voxel size, field strength, coil array, etc., you could include more cycles and may need to average together multiple runs.

Below are a few nice papers which discuss some of these details relating to phase-encoded retinotopic stimuli.

Sereno & Tootell. Curr Opin Neurobiol. 2005;15(2):135-44. (discusses the use of smoothly varying stimuli)

Tootell et al. J Neurosci. 1997;17(18):7060-78. (discusses the ring/wedge thickness)

Sereno et al. Science. 1995;268(5212):889-93. (discusses the advantages of using both expanding + contracting stimuli)