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

Zappe AC, Uludağ K, Oeltermann A, Uğurbil K, Logothetis NK - Cereb. Cortex (2008)

Bottom Line: Such methods, however, assume that hypercapnia has no direct effect on CMRO(2).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 approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg).A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg).

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute for Biological Cybernetics, Spemannstrasse 38, 72076 Tübingen, Germany. aczappe@tuebingen.mpg.de

ABSTRACT
Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO(2) is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO(2)) 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 approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg). This suggests that CMRO(2) might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal.

Show MeSH

Related in: MedlinePlus

The averaged time course of gamma and MUA electrophysiological responses after the onset of 6% CO2 inhalation. In 2 out of 5 sessions, the amplitude of change was much stronger for MUA than for gamma range, which was still visible in the group average. The beta band was noisier and thus not included in the figure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2567427&req=5

fig3: The averaged time course of gamma and MUA electrophysiological responses after the onset of 6% CO2 inhalation. In 2 out of 5 sessions, the amplitude of change was much stronger for MUA than for gamma range, which was still visible in the group average. The beta band was noisier and thus not included in the figure.

Mentions: The first 6 min of gamma and MUA activity directly after the onset of 6% CO2 inhalation are depicted in Figure 3 (transient hypercapnia phase). For display purposes, the time course of beta activity is not shown. The beta band showed the same trend as the gamma and MUA bands, but the time course has lower signal-to-noise ratio (compare Fig. 2A). In particular, the time courses vary greatly from session to session and over electrodes within a session. In 2 out of 5 sessions the decrease was found to be stronger for MUA than for the gamma range. In the remaining sessions the changes were of comparable size. For the onset of 3% CO2 none of the 3 bands showed significant decreases.


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

Zappe AC, Uludağ K, Oeltermann A, Uğurbil K, Logothetis NK - Cereb. Cortex (2008)

The averaged time course of gamma and MUA electrophysiological responses after the onset of 6% CO2 inhalation. In 2 out of 5 sessions, the amplitude of change was much stronger for MUA than for gamma range, which was still visible in the group average. The beta band was noisier and thus not included in the figure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2567427&req=5

fig3: The averaged time course of gamma and MUA electrophysiological responses after the onset of 6% CO2 inhalation. In 2 out of 5 sessions, the amplitude of change was much stronger for MUA than for gamma range, which was still visible in the group average. The beta band was noisier and thus not included in the figure.
Mentions: The first 6 min of gamma and MUA activity directly after the onset of 6% CO2 inhalation are depicted in Figure 3 (transient hypercapnia phase). For display purposes, the time course of beta activity is not shown. The beta band showed the same trend as the gamma and MUA bands, but the time course has lower signal-to-noise ratio (compare Fig. 2A). In particular, the time courses vary greatly from session to session and over electrodes within a session. In 2 out of 5 sessions the decrease was found to be stronger for MUA than for the gamma range. In the remaining sessions the changes were of comparable size. For the onset of 3% CO2 none of the 3 bands showed significant decreases.

Bottom Line: Such methods, however, assume that hypercapnia has no direct effect on CMRO(2).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 approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg).A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg).

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute for Biological Cybernetics, Spemannstrasse 38, 72076 Tübingen, Germany. aczappe@tuebingen.mpg.de

ABSTRACT
Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO(2) is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO(2)) 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 approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg). This suggests that CMRO(2) might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal.

Show MeSH
Related in: MedlinePlus