Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 99, Issue 16, Pages 10765-10770Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.132272199
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Funding
- NICHD NIH HHS [P01 HD032573, HD-32573] Funding Source: Medline
- NIDCD NIH HHS [DC-003710, R01 DC003710] Funding Source: Medline
- NIDDK NIH HHS [R01 DK027121, DK-27121] Funding Source: Medline
- NINDS NIH HHS [R01 NS034813, NS-34813, NS-32126] Funding Source: Medline
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Functional MRI (fMRI) is widely assumed to measure neuronal activity, but no satisfactory mechanism for this linkage has been identified. Here we derived the changes in the energetic component from the blood oxygenation level-dependent (BOLD) fMRI signal and related it to changes in the neuronal spiking frequency in the activated voxels. Extracellular recordings were used to measure changes in cerebral spiking frequency (Deltanu/nu) of a neuronal ensemble during forepaw stimulation in the alpha-chloralose anesthetized rat. Under the same conditions localized changes in brain energy metabolism (DeltaCMR(O2)/CMRO2) were obtained from BOLD fMRI data in conjunction with measured changes in cerebral blood flow (DeltaCBF/CBF), cerebral blood volume (DeltaCBV/CBV), and transverse relaxation rates of tissue water (T-2* and T-2) by MRI methods at 7T. On stimulation from two different depths of anesthesia DeltaCMR(O2)/CMRO2 approximate to Deltanu/nu. Previous C-13 magnetic resonance spectroscopy studies, under similar conditions, had shown that DeltaCMR(O2)/CMRO2 was proportional to changes in glutamatergic neurotransmitter flux (DeltaV(cyc)/V-cyc). These combined results show that DeltaCMR(O2)/CMRO2 approximate to DeltaV(cyc)/V-cyc approximate to Deltanu/nu, thereby relating the energetic basis of brain activity to neuronal spiking frequency and neurotransmitter flux. Because DeltaCMR(O2)/CMRO2 had the same high spatial and temporal resolutions of the fMRI signal, these results show how BOLD imaging, when converted to DeltaCMR(O2)/CMRO2, responds to localized changes in neuronal spike frequency.
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