Evaluation of activity-dependent functional pH and T response in the visual cortex

Hye Young Heo, John Wemmie, Daniel Thedens, Vincent A. Magnotta

Research output: Contribution to journalArticlepeer-review

Abstract

Recent experiments suggest that T1 relaxation in the rotating frame (T) detects localized metabolic changes in the human visual cortex induced by a flashing checkerboard task. Possible sources of the T signal include pH, glucose, and glutamate concentrations as well as changes in cerebral blood volume. In this study we explored the relationship of the T signal changes related to cerebral blood volume changes by employing inferior saturation pulses. Our hypothesis was that there would be a contribution of cerebral blood volume to the functional T signal, but a majority of the signal would correspond to metabolic changes. In addition, the relationship between T and pH was explored by manipulating the frequency of the flashing checkerboard and imaging with T, BOLD, and 31P spectroscopy. We hypothesized that T and pH changes would be sensitive to the stimulation frequency. To test this hypothesis, we used a full-field visual flashing checkerboard and varied the frequency between 1, 4, and 7Hz. Supporting our hypotheses, we found that approximately 73% of the measured signal change corresponds to metabolism in vivo and that increasing stimulation frequency increased responses measured by all three imaging modalities. The activation area detected by T overlapped to a large degree with that detected by BOLD, although the T response area was significantly smaller. 31P spectroscopy detected a greater acidosis with the higher stimulation frequencies. These observations suggest that, similar to the BOLD response, the magnitude of the T and pH response depends on stimulation frequency and is thus likely to be activity-dependent.

Original languageEnglish (US)
Pages (from-to)336-343
Number of pages8
JournalNeuroImage
Volume95
DOIs
StatePublished - Jul 15 2014

Keywords

  • BOLD
  • Brain activation
  • Brain pH

ASJC Scopus subject areas

  • Neurology
  • Cognitive Neuroscience

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