Neuroscience 2005 Abstract
| Presentation Number: | 285.8 |
|---|---|
| Abstract Title: | Functional MRI can measure timing of transient increases in neural response with high precision. |
| Authors: |
Harley, E.*1
; Carr, V. A.1
; Viskontas, I. V.1
; Cohen, M. S.2
; Engel, S. A.1
1Psychology, UCLA, Los Angeles, CA 2Psychiatry, UCLA, Los Angeles, CA |
| Primary Theme and Topics |
Sensory and Motor Systems - Vision -- Processing of contrast, orientation, form, and color |
| Session: |
285. Visual Cortex: Temporal Dynamics Poster |
| Presentation Time: | Sunday, November 13, 2005 4:00 PM-5:00 PM |
| Location: | Washington Convention Center - Hall A-C, Board # Y16 |
| Keywords: | IMAGING, FMRI, CONTRAST, TIMING |
Prior studies have used fMRI to measure the onset of neural activity from a stable baseline with a temporal precision on the order of 100 msec. Many important neural processes, however, reveal themselves as increases in activity that lie on top of another neural response. We attempted to determine whether fMRI could measure the timing of an increase that occurred 200 msec after initial response. Subjects viewed stimuli from three conditions. In our baseline condition, a low contrast flickering checkerboard was presented for 600 msec. We added a 400 msec contrast increment to this stimulus either at a 200 msec delay or immediately upon stimulus presentation; thus in the delay condition the low contrast checkerboard increased its contrast after 200 msec and remained high contrast for 400 msec, while in the immediate condition a high contrast flickering checkerboard reduced its contrast after 400 msec and remained low for 200 msec. We acquired BOLD fMR images every 100 msec (TR) while these conditions were presented in a rapid event-related design. We averaged data within primary visual cortex and computed conditional hemodynamic timecourses using standard linear methods and ordinary least-squares. Subtracting the baseline response from the responses to the delay condition and the immediate condition generated difference timecourses that isolated the transient increase in response. The two difference timecourses were similar in shape, and in all three subjects the delay difference timecourse peaked later than the immediate difference timecourse. To quantify the delay in activity, we computed the center of mass of each difference timecourse; the center of mass of the delay difference timecourse was on average 160 msec +- 50 (s.d.) later in time than the center of mass of the immediate difference timecourse. These results demonstrate that fMRI can detect relatively small differences in the timing of increases in neural activity, even when the increases lie on top of a substantial response.
Supported by NIH EY11862
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2005 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2005. Online.
Copyright © 2005-2025 Society for Neuroscience; all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.
