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Characterization of the functional response in the human spinal cord: Impulse-response function and linearity
Giovanni Giulietti1, Federico Giove, Girolamo Garreffa
1MARBILab, Museo storico della fisica e Centro di studi e ricerche Enrico, Fermi, 00184 Roma, Italy.
Neuroimage
|July 5, 2008
Summary
Functional magnetic resonance imaging (fMRI) of the human spinal cord shows a delayed, larger signal than in the brain for motor tasks. This technique reveals linear behavior for longer stimulations but deviates during short ones.
Area of Science:
- Neuroimaging
- Spinal Cord Physiology
- Functional Magnetic Resonance Imaging
Background:
- Functional magnetic resonance imaging (fMRI) is a key tool for brain function studies.
- Applying fMRI to the human spinal cord has yielded controversial results due to poorly characterized functional contrast and debated origins.
Purpose of the Study:
- To characterize the temporal features of the functional signal in the human spinal cord during motor tasks.
- To investigate the linearity and physiological basis of spinal cord fMRI signals.
Main Methods:
- Utilized time-locked averaging of functional time series of varying durations.
- Defined an impulse-response function (irf) to model the spinal cord's functional response.
- Compared spinal cord fMRI signal characteristics to those observed in the brain.
Main Results:
- An impulse-response function explained spinal cord motor responses for stimulation durations of 15-42 seconds, indicating linearity.
- Functional signals were undetectable or below linear predictions for shorter stimulations (3-9 seconds), suggesting non-linear behavior.
- The spinal cord impulse-response function was slower than the brain's, peaking around 9 seconds.
- Observed contrast in the spinal cord was larger than in the brain (approx. 5.4% at 1.5 T).
Conclusions:
- The physiological origin of T(2)-weighted functional imaging appears similar in the spinal cord and brain.
- Spinal cord fMRI exhibits distinct temporal dynamics compared to the brain, with linearity observed for longer motor task durations.
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