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Consistency and variability in functional localisers

Authors
Journal
NeuroImage
1053-8119
Publisher
Elsevier
Publication Date
Volume
46
Issue
4
Identifiers
DOI: 10.1016/j.neuroimage.2009.03.014
Keywords
  • Fmri
  • Reading
  • Object Recognition
  • Posterior Fusiform Gyrus
  • Functional Localiser
  • Occipito-Temporal Cortex
Disciplines
  • Design

Abstract

Abstract A critical assumption underlying the use of functional localiser scans is that the voxels identified as the functional region-of-interest (fROI) are essentially the same as those activated by the main experimental manipulation. Intra-subject variability in the location of the fROI violates this assumption, reducing the sensitivity of the analysis and biasing the results. Here we investigated consistency and variability in fROIs in a set of 45 volunteers. They performed two functional localiser scans to identify word- and object-sensitive regions of ventral and lateral occipito-temporal cortex, respectively. In the main analyses, fROIs were defined as the category-selective voxels in each region and consistency was measured as the spatial overlap between scans. Consistency was greatest when minimally selective thresholds were used to define “active” voxels ( p < 0.05 uncorrected), revealing that approximately 65% of the voxels were commonly activated by both scans. In contrast, highly selective thresholds ( p < 10 − 4 to 10 − 6 ) yielded the lowest consistency values with less than 25% overlap of the voxels active in both scans. In other words, intra-subject variability was surprisingly high, with between one third and three quarters of the voxels in a given fROI not corresponding to those activated in the main task. This level of variability stands in striking contrast to the consistency seen in retinotopically-defined areas and has important implications for designing robust but efficient functional localiser scans.

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