Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/3727

Title

Efficient retinotopic mapping of occipital cortex through application of a multi-focal paradigm to fMRI

Author(s)

Crewther, David P.;  Crewther, Sheila;  Foster, Brett L.

Abstract

The visual multi-focal evoked potential paradigm, whereby multiple independent responses to spatially separate stimuli are acquired in a single recording, has been thoroughly investigated using electrophysiological modalities. The present study aimed to perform similar measurements using fMRI. Participants (N = 6) viewed a circle divided into 9 regions (comprising of four peripheral and central quadrants and a central foveal region) for 10 minutes. The total stimulus subtended 8 deg of visual field and individual patches were scaled in area, with peripheral patches 16 times the area of the foveal patch. Each region alternated between 'on' (concentric/radial lines) and 'off' (gray) states every TR (2.5s) in a pseudo-random fashion generated via an m-sequence. T2 * weighted images were acquired during the experimental condition at 3T (21 slices). Application of an m-sequence stimulus presentation design allowed for separate analysis of stimulus regions which were presented simultaneous in a single recording session. Statistical analysis showed that each of the large peripheral patches caused highly significantly BOLD responses in primary visual cortex, with significant findings occurring in both group and single subject analysis. Furthermore, significant findings also showed reasonable retinotopic mapping when visualized on an inflated cortical surface. However, smaller central patches did not provide similar significant activations. While the stimulus was designed for approximately equal cortical representation for each patch, we suggest that the lack of significant findings for central patches reflects their greater susceptibility to eye movements (foveal patch subtended only 0.5 deg). In conclusion, the application of multi-focal based stimulus presentation sequences (m-sequence) may be beneficial to other types of stimulus design used in event-related fMRI.

Publication type

Conference poster

Research centre

Swinburne University of Technology. Faculty of Life and Social Sciences

Source

Paper presented at the 10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004), Budapest, Hungary, 13-17 June 2004

Publication year

2004

Publisher

Academic Press

Publisher URL

http://www.conferences.hu/hbm2004/