Abstract
Because of well-known nonlinearities in fMRI, responses measured with rapid event-related designs are smaller than responses measured with spaced designs. Surprisingly, no study to date has tested whether rapid designs also change the pattern of responses across different stimulus conditions. Here we report the results of such a test. We measured cortical responses to a flickering checkerboard at different contrasts using rapid and spaced event-related fMRI. The relative magnitude of responses across contrast conditions differed between rapid and spaced designs. Modeling the effect of the rapid design as a scaling of stimulus strength provided a good account of the data. The data were less well fit by a model that scaled the strength of responses. A similar stimulus scaling model has explained effects of neural adaptation, which suggests that adaptation may account for the observed difference between rapid and spaced designs. In a second experiment, we changed the stimulus in ways known to reduce neural adaptation and found much smaller differences between the two designs. Stimulus scaling provides a simple way to account for nonlinearities in event-related fMRI and relate data from rapid designs to data gathered using slower presentation rates.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 651-660 |
| Number of pages | 10 |
| Journal | NeuroImage |
| Volume | 34 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jan 15 2007 |
Bibliographical note
Funding Information:The authors wish to thank Mark Cohen for helping with fMRI. For generous support of the UCLA Brain Mapping facility, the authors also wish to thank John Mazziotta, the Brain Mapping Medical Research Organization, Brain Mapping Support Foundation, Pierson-Lovelace Foundation, The Ahmanson Foundation, William M. and Linda R. Dietel Philanthropic Fund at the Northern Piedmont Community Foundation, Tamkin Foundation, Jennifer Jones-Simon Foundation, Capital Group Companies Charitable Foundation, Robson Family and Northstar Fund. The facility is supported by Grant Numbers RR12169, RR13642 and RR00865 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH); the paper's contents are solely the responsibility of the authors and do not necessarily represent the official views of NCRR or NIH. This work was supported by NIH EY11862 to S.E., NSF graduate fellowship to G.H., and NIH MH015795.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.