Investigation of possible high-energy phosphate concentration changes in the visual cortex for different stimulus frequencies
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Many works have reported changes in the visual cortex regarding stimulation with different flickering frequencies using various neuroimaging techniques. Also, many phosphorus functional magnetic resonance spectroscopy (31P-fMRS) studies have reported high-energy phosphate (HEP) changes in the visual cortex during visual stimulation at 8 Hz, compared with rest periods. However, there have been no studies attempting to measure HEP changes during visual stimulation with different flickering frequencies. The aim of this work was to use the 31P-fMRS technique to assess possible HEP changes during visual stimulation experiments with stimuli flickering at 4 Hz or 8 Hz, and compare the results obtained with the different frequencies.
Nineteen subjects participated in the study. Experiments consisted of 31P-fMRS acquisitions in a 3T magnetic resonance scanner while subjects underwent a five blocks Rest/Stimulus protocol, with stimuli flickering at either 4 Hz or 8 Hz. We assessed pH; the alpha and gamma peaks of adenosine tri-phosphate (α-ATP and γ-ATP); the ratios phosphocreatine/inorganic phosphate (Pi), and of the metabolites phosphocreatine, Pi, glycerophosphocholine, phosphoethanolamine, and glycerophosphoethanolamine with respect to α-ATP and γ-ATP; and the linewidth of the phosphocreatine peak.
pH was stable along acquisitions for both 4 Hz and 8 Hz. No significant changes were found for neither α-ATP, γ-ATP, metabolite ratios, nor phosphocreatine linewidth.
This was probably due to the compromise existing between signal-to-noise ratio and temporal/spatial resolutions—the former requires long acquisitions/large voxels which possibly result in missing alterations and partial volume effects regarding changes detected by other techniques such as functional magnetic resonance imaging. These effects may have been amplified by the use of a non-localized sequence.
KeywordsPhosphorus magnetic resonance spectroscopy Functional experiments Brain activation Visual cortex Stimulus frequency
This work was supported by São Paulo Research Foundation (FAPESP, Brazil) (grant numbers 2005/56578-4, 2009/00270-2, 2009/10046-2, 2011/01106-1, 2013/07559-3), National Council of Scientific and Technological Development (CNPq, Brazil) (grant number 500148/2011-2), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil) (Finance Code 001).
Compliance with ethical standards
The project was approved by the Ethics Committee of University of Campinas (CAAE 0568.0.146.000–09), and written informed consent was obtained from all subjects, prior to data acquisition.
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