fMRI Retinotopic Mapping—Step by Step

Abstract

fMRI retinotopic mapping provides detailed information about the correspondence between the visual field and its cortical representation in the individual subject. Besides providing for the possibility of unambiguously localizing functional imaging data with respect to the functional architecture of the visual system, it is a powerful tool for the investigation of retinotopic properties of visual areas in the healthy and impaired brain. fMRI retinotopic mapping differs conceptually from a more traditional volume-based, block-type, or event-related analysis, in terms of both the surface-based analysis of the data and the phase-encoded paradigm. Several methodological works related to fMRI retinotopic mapping have been published. However, a detailed description of all the methods involved, discussing the steps from stimulus design to the processing of phase data on the surface, is still missing. We describe here step by step our methodology for the complete processing chain. Besides reusing methods proposed by other researchers in the field, we introduce original ones: improved stimuli for the mapping of polar angle retinotopy, a method of assigning volume-based functional data to the surface, and a way of weighting phase information optimally to account for the SNR obtained locally. To assess the robustness of these methods we present a study performed on three subjects, demonstrating the reproducibility of the delineation of low order visual areas.

Visual Topography of Human Intraparietal Sulcus

“…We generated cross-session phase estimates by first weighting the real and imaginary phase components of each session by the within-session F ratio, multiplied by the number of runs in the session. This weighting is proportional to the square of the within-session signal-to-noise ratio (SNR), which is the least-squares optimal weighting for a combined phase estimate at moderate to high SNR (Warnking et al, 2002). The resulting weighted real and imaginary components were then summed vertexwise over the cortical surface, and the final vector sum at each vertex was converted back into an angular phase measurement.…”

Spatial resolution of EEG cortical source imaging revealed by localization of retinotopic organization in human primary visual cortex

“…motor/sensory-related tasks (Darvas et al, 2004) and tonotopic organization of human auditory cortex (Talavage et al, 2004). In particular, the retinotopic activity in the human visual cortex (Sereno et al, 1995;DeYoe et al, 1996;Engel et al, 1997;Warnking et al, 2002;Grill-Spector and Malach 2004) has been well studied. The retinotopic maps constructed using fMRI have been frequently applied to visual ERP studies in order to identify functional or anatomical locations of the localized ERP sources Di Russo et al, 2005).…”

Shift-invariant multilinear decomposition of neuroimaging data

“…the right and left hemisphere. These delays corresponded to the delays obtained from a traditional voxelwise DFT analysis (Sereno et al, 1995;Engel et al, 1997;Warnking et al, 2002). DFT assumes the time series for the delay modeling is sinusoidal and constant in strength over the epochs.…”