Neuroscience 2003 Abstract
| Presentation Number: | 548.7 |
|---|---|
| Abstract Title: | Functional MRI of human primary olfactory cortex, rate-encoding versus temporal-encoding. |
| Authors: |
Johnson, B. N.*1
; Mainland, J. D.2
; Bensafi, M.2
; Khan, R. M.2
; Sobel, N.1,2,3
1BioEngin., Univ. of California at Berkeley, Berkeley, CA 2Helen Wills Neurosci., Univ. of California at Berkeley, Berkeley, CA 3Psychology, Univ. of California at Berkeley, Berkeley, CA |
| Primary Theme and Topics |
Sensory Systems - Chemical senses -- Olfaction: Olfactory coding |
| Session: |
548. Olfaction II Slide |
| Presentation Time: | Tuesday, November 11, 2003 9:30 AM-9:30 AM |
| Location: | Morial Convention Center - Room 268 |
| Keywords: | OLFACTION, CODING, FMRI, FUNCTIONAL MRI |
Functional magnetic resonance imaging (fMRI) of primary olfactory cortex (POC) has yielded inconsistent results. Odorant-induced POC activity is present at times and absent at others even within the same lab using the same task. Most statistical models used to analyze fMRI data rely on two assumptions: 1. a monotonic transform from stimulus magnitude to neural activity quantity, and 2. a linear transform from neural activity quantity to MR signal magnitude. Whereas the latter has been demonstrated for MR (Boynton et al 1996), the former has not been demonstrated for POC. An equally viable alternative to a rate-encoding model is a temporal-encoding model. Models of temporal-encoding imply no monotonic transform from stimulus magnitude to neural activity quantity. Thus, fMRI is a potentially invalid measure of POC activity under temporal-encoding models. To address this issue we set out to quantify the stimulus magnitude dependence in POC in thirty subjects. An olfactometer generated low, medium and high concentrations of the odorants valeric acid, phenethyl alcohol, and propionic acid in an event-related design (4T, T2* GEMS, TE=28ms, TR=1sec, 192mm FOV, 8 slices, 0.5mm skip, 3x3x3.5mm voxel, ISI=30sec, stimulus repetition=27). The initial 6 subjects of propionic acid had significant activation overall in lateral orbital fronal cortex (p<.05) and in POC (F(3,20)=3.44, p<.03). The relationship between increased signal and increased stimulus concentration in POC was monotonic but not linear (approximately logarithmic). We will test if this finding is the nature of POC encoding or is the consequence of another factor. For example, in several of these initial subjects the signal in POC appeared to be confounded by individual sniff dynamics. Final data analysis will include regressors based on individual sniffs to reduce this variability.
Supported by SOSI & NIH-NIDCD R03-DC05141-2
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2003 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2003. Online.
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