Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/3724

Title

Efficient mapping of multiple attributes with fMRI and individual variation

Author(s)

Crewther, David P.;  Crewther, Sheila G.;  Foster, Brett L.;  Rutkowski, Jacqueline S.;  Waites, Tony;  Wheaton, Kylie J.

Abstract

Our aim was to produce functional activation landmark maps in an efficient fashion. While our conscious percept seems to be single valued ? that is, we seem to have a single stream of consciousness, it is possible that stimuli containing several different descriptive attributes might simultaneously activate different brain regions. This is certainly true of spatially segregated stimulus regions which can contribute simultaneously to a topographically organized map (see Foster et al HBM2004), however it is not clear whether attributes such as object identity, its motion characteristic and its colour can be ?unbound? in terms of simultaneous activation of the relevant brain regions. To this end we created a series of multi-attribute stimuli which encapsulated attributes in a binary fashion: (face vs jumble face) X (colour vs grey) X (moving vs stationary) X (saccadic eye movements vs fixation), i.e. there were 16 conditions (e.g. a stationary coloured face across which saccadic eye movements were made, or, a moving grey jumble for which the eyes remain focused on a fixed location). The individual attributes were ordered in a pseudo-random fashion such that correlations between stimulus sequences was close to zero (Bartlett's test of sphericity, Chi Square = 1.14, p = 0.999). As a comparison (to create localisers), four scans involving individual pseudorandom sequences of the individual contrasts (face vs jumble face, colour vs grey, moving vs stationary, saccadic eye movements vs fixation) were performed. Each stimulus was presented for 2.5 sec (corresponding to the TR value of the fMRI acquisition). Thus in the multi-attribute scan involving one 5 minute acquisition of 128 volumes, the four separate contrasts were imaged without a loss of statistical power (of the 128 volumes, 64 showed faces and 64 showed jumbles; similarly, 64 were coloured while 64 were grey, etc). The four localisers required 4x128 = 512 volumes to be acquired. Six normal adult subjects volunteered. The T2* images were acquired on the 3T magnet at the BRI/ARMC in Melbourne, and were analysed using Brain Voyager and SPM99. For the Localiser activations, Strong face vs jumble differential activation was observed in fusiform cortex for 3 of the 6 subjects with weaker activation in the others. Similarly, consistent differential activation was observed in the region of V5/MT+ for motion vs stationary stimuli. Eye movement vs fixation produced less consistent activation in frontal cortex across subjects while colour vs grey showed inconsistent activation in extrastriate cortex. For the Multi-Attribute activations, overall activation was, if anything, greater than for the individual localisers for individual subjects. In one subject, significant activations for 3 of the 4 contrasts (face, movement, colour) were clearly identifiable, but eye movement while causing activation in the localiser did not result in a clear activation in the multi-attribute acquisition. For other individuals, the pattern of activation was variable with face and movement the most robust activations. We conclude that multi-attribute mapping is possible, however, the relative activation is variable, perhaps reflecting differences in attribute salience to each individual.

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/