Effects of changes in end‐tidal PO 2 and PCO 2 on neural responses during rest and sustained attention

Figures

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  FIGURE 1. Methods (a) participant instrumentation. Participants were fitted with EEG electrodes, transcranial Doppler ultrasound, ECG, and a respiratory mask connected to a dynamic end‐tidal forcing system. (b) Schematic example of the behavioral task. During the “task” phase, participants monitored a centrally presented circular annulus that alternated between red and green. A button‐press response was made when a slightly longer duration target (10% of trials) was detected. A large checkerboard pattern was presented in the background with a contrast pattern that reversed every 8.33 Hz in order to drive a steady‐state response in the cortex. (c) Gas challenge protocol. Each gas challenge condition began with 5 min of air breathing to establish steady‐state breathing, followed by a 3‐min isocapnia‐euoxia baseline period, and then 5 min at the desired gas concentration to achieve steady‐state conditions before beginning the attention rest/task protocol. Participants then alternated between 45 s of rest (fixating on a white dot presented at the center of the screen) and 45 s of the behavioral task. After completing eight full cycles (12 min total), participants then breathed room air for 10…

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  FIGURE 2. Behavior (a) proportion of “hits” (correctly detected targets). A dashed horizontal line represents chance performance. (b) RTs to correctly detect targets. There was no significant effect of gas condition on hits or RT. Error bars represent ± SEM

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  FIGURE 3. End‐tidal traces. Mean Peto 2 and Petco 2 traces are plotted, collapsed across all eight 90 s rest (0–45 s)/task (45–90s) cycles for each gas challenge condition, and averaged over all participants. Error bars represent ± SEM

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  FIGURE 4. Cerebral blood flow and electroencephalographic activity over rest/task cycle. (a) Middle cerebral artery velocity (MCAv) and (b) posterior cerebral artery velocity (PCAv) were measured over a full 90 s rest/task cycle. (c) Alpha power computed over a full cycle (lines represent mean of PO/O electrode activity). Each line represents data averaged over all participants and trial blocks. Error bars represent ± SEM

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  FIGURE 5. Cerebral blood flow analyses. (a) Middle cerebral artery velocity (MCAv) and (b) posterior cerebral artery velocity (PCAv) averaged over the final 15 s of rest (R) and task (T) phases. (c) Percent change in CBF velocity (CBFv) in PCA (P) and MCA (M) from rest to task phase (normalized to the final 15 s of rest phase). (d) MCA cerebrovascular conductance (MCAcvc) and (e) PCA cerebrovascular conductance (PCAcvc) averaged over the final 15 s of rest (R) and task (T) phases. (f) Percent change in CBFcvc in PCA (P) and MCA (M) from rest to task phase (normalized to the final 15 s of rest phase). Error bars represent ± SEM

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  FIGURE 6. Spectral electroencephalographic and neurovascular coupling analyses. (a) Spectral power during rest and task phases. Data represent the mean of PO/O electrodes. The shaded area represents alpha frequencies used for subsequent calculations. (b) Distribution of alpha across the scalp during rest and task phases. (c) Alpha power (mean of PO/O electrodes). (d) Distribution of steady‐state visual evoked potential (SSVEP) activity [second harmonic; 16.67 Hz] across the scalp during the task phase. (e) SSVEP amplitude (mean of PO/O electrodes). (f) Alpha power regressed against posterior cerebral artery velocity and middle cerebral artery velocity at 1 s intervals across a full rest/task epoch (horizontal line at the base of plot indicates time points, where p null < 0.05). Error bars represent ±SEM

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  FIGURE 7. Event‐related electroencephalographic data analyses. (a) Event‐related potentials (ERPs) were computed using mean activation over central, parietal, and parieto‐occipital electrodes for correctly detected target trials. Plots reveal a robust P3 ERP component emerging ~300 ms after the onset of the target period (0 ms). Thick horizontal black and blue bars represent significant ANOVA and pairwise comparisons (p null < 0.05). (b) Distribution of P3 ERP activity across the scalp between 400 and 600 ms during correctly detected target trials. (c) Event‐related spectral perturbations (ERSPs) plots show the time course of spectral activation during standard trials in the task phase. Each plot represents activation averaged across parietal and parieto‐occipital and occipital electrodes. Black rectangles denote time–frequency regions that are significantly different according to the ANOVA tests. (d) Bars represent mean activation for regions highlighted in the ERSP plots. Pairwise comparisons indicate that differences in the time–frequency plots are driven by reduced theta and alpha in Hpo relative to IsoEu (*p null < 0.05). Error bars represent ±SEM

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  FIGURE 8. Control analyses. Behavioral performance and physiologic responses were recorded during the isocapnic hyperventilation control condition (Hv) and compared with the hypocapnia condition (Hpo). (a) Proportion of “hits” (correctly detected targets). A dashed horizontal line represents chance performance. (b) RTs to correctly detect targets. (c) Mean Peto 2 and Petco 2 traces are plotted, collapsed across all eight 90 s rest (0–45 s)/task (45–90 s) cycles for the Hv condition. (d–f) Middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv), and alpha power (mean of PO/O electrodes), respectively. (g) MCAv and (h) PCAv averaged across the final 15 s of rest and task phases. (i) Percent change in CBFv in PCA and MCA from rest to task phase (normalized to the final 15 s of rest phase). (j) MCA cerebrovascular conductance (MCAcvc) and (k) PCA cerebrovascular conductance (PCAcvc) averaged across the final 15 s of rest and task phases. (l) Percent change in cerebral blood flow cerebrovascular conductance (CBFcvc) in PCA and MCA from rest to task phase (normalized to the final 15 s of rest phase). Error bars represent ±SEM

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  FIGURE 9. Spectral electroencephalographic and neurovascular coupling control analyses (a) Mean spectral power during rest and task phases. Lines on plot represent the mean of PO/O electrodes. The shaded area represents the alpha frequency band (9–12 Hz). (b) Topographic plots reflect the distribution of alpha activity (9–12 Hz) across the scalp during rest and task phases. (c) Bars represent mean alpha amplitude in each condition (mean of PO/O electrodes). (d) Distribution of steady‐state visual evoked potential (SSVEP) activity (second harmonic; 16.67 Hz) across the scalp during the task phase. (e) SSVEP amplitude (mean of PO/O electrodes). (f) Plots represent alpha power regressed against posterior cerebral artery and middle cerebral artery at 1 s intervals across a full rest/task epoch (horizontal line at the base of plot indicates significant results at p null < 0.05). Error bars represent ±SEM

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  FIGURE 10. Event‐related electroencephalographic control data analyses. (a) Event‐related potentials (ERPs) were computed using the mean of central, parietal, and parieto‐occipital electrodes for correctly detected target trials. Plots reveal a robust P3 ERP component in both gas conditions. 0 ms represents the onset of the target period. Horizontal bars depict significant statistical tests (p null < 0.05). (b) Distribution of P3 ERP activity across the scalp between 400 and 600 ms during correctly detected target trials. (c) Event‐related spectral perturbations (ERSPs) plots show the time course of spectral activation during standard trials in the task phase, averaged across parietal, parieto‐occipital, and occipital electrodes. Black boxes highlight significant differences in theta and alpha activation. (d) Bars represent mean spectral time–frequency activation for regions highlighted in the ERSP plots. Error bars represent ±SEM