The influence of moderate hypercapnia on neural activity in the anesthetized nonhuman primate

Nikos Logothetis, A. C. Zappe, K. Uludaǧ, A. Oeltermann, K. Uǧurbil, N. K. Logothetis

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    Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO2 is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO2) by measuring cerebral blood flow and blood-oxygenation-level-dependent (BOLD) signal. Such methods, however, assume that hypercapnia has no direct effect on CMRO 2. In this study, we used combined intracortical recordings and fMRI in the visual cortex of anesthetized macaque monkeys to show that spontaneous neuronal activity is in fact significantly reduced by moderate hypercapnia. As expected, measurement of cerebral blood volume using an exogenous contrast agent and of BOLD signal showed that both are increased during hypercapnia. In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by ∼15% during inhalation of 6% CO2 (pCO2 = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO 2 inhalation of 3% (pCO2 = 45 mmHg). This suggests that CMRO2 might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal. © 2008 The Authors.
    Original languageEnglish
    Pages (from-to)2666-2673
    Number of pages7
    JournalCerebral Cortex
    Issue number11
    Publication statusPublished - Nov 2008


    • Cerebral cortex
    • Extracellular recording
    • fMRI
    • Macaque
    • Metabolism
    • Neurovascular coupling
    • Striate cortex


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