Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 102, Issue 10, Pages 3822-3827Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0407789102
Keywords
barrel cortex; blood oxygenation; intrinsic signals; optical imaging
Categories
Funding
- NCRR NIH HHS [P41 RR014075, P41 RR 14075] Funding Source: Medline
- NIBIB NIH HHS [R01 EB 00790, R01 EB000790] Funding Source: Medline
- NINDS NIH HHS [R01 NS044623, NS 44623] Funding Source: Medline
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Accurate interpretation of functional MRI,(fMRI) signals requires knowledge of the relationship between the hemodynamic response and the neuronal activity that underlies it. Here we address the question of coupling between pre- and postsynaptic neuronal activity and the hemodynamic response in rodent somatosensory (Barrel) cortex in response to single-whisker deflection. Using full-field multiwavelength optical imaging of hemoglobin oxygenation and electrophysiological recordings of spiking activity and local field potentials, we demonstrate that a point hemodynamic measure is influenced by neuronal activity across multiple cortical columns. We demonstrate that the hemodynamic response is a spatiotemporal convolution of the neuronal activation. Therefore, positive hemodynamic response in one cortical column might be explained by neuronal activity not only in that column but also in the neighboring columns. Thus, attempts at characterizing the neurovascular relationship based on point measurements of electrophysiology and hemodynamics may yield inconsistent results, depending on the spatial extent of neuronal activation. The finding that the hemodynamic signal observed at a given location is a function of electrophysiological activity over a broad spatial region helps explain a previously observed increase of local vascular response beyond the saturation of local neuronal activity. We also demonstrate that the oxy- and total-hemoglobin hemodynamic responses can be well approximated by space.-time separable functions with an antagonistic center-surround spatial pattern extending over several millimeters. The surround negative hemodynamic activity did not correspond to observable changes in neuronal activity. The complex spatial integration of the hemodynamic response should be considered when interpreting fMRl data.
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