Spaceflight missions to the International Space Station (ISS) expose astronauts to microgravity, radiation, isolation, and elevated carbon dioxide (CO2), among other factors. Head down tilt bed rest (HDBR) is an Earth-based analog for spaceflight used to study body unloading, fluid shifts, and other factors unrelated to gravitational changes. While in space, astronauts need to use mental rotation strategies to facilitate their adaptation to the ISS environment. Therefore, spatial working memory is essential for crewmember performance. Although the effects of HDBR on spatial working memory have recently been studied, the results are still inconclusive. Here, we expand upon past work and examine the effects of HDBR with elevated CO2 (HDBR + CO2) on brain activation patterns during spatial working memory performance. In addition, we compare brain activation between 30 days of HDBR + CO2 and 70 days of HDBR to test the isolated effect of CO2. Eleven subjects (6 males, 5 females; mean age = 34 ± 8 years) underwent six functional magnetic resonance imaging (fMRI) sessions pre-, during, and post-HDBR + CO2. During the HDBR + CO2 intervention, we observed decreasing activation in the right middle frontal gyrus and left regions of the cerebellum, followed by post-intervention recovery. We detected several correlations between brain and behavioral slopes of change with the HDBR + CO2 intervention. For example, greater increases in activation in frontal, temporal and parietal regions were associated with larger spatial working memory improvements. Comparing the HDBR + CO2 group to data from our previous 70-day HDBR study, we found greater decreases in activation in the right hippocampus and left inferior temporal gyrus for the HDBR + CO2 group over the course of the intervention. Together, these findings increase our understanding of the neural mechanisms of HDBR, elevated levels of CO2 and spaceflight-related changes in spatial working memory performance. Graphical Abstract Top: previous findings regarding spatial working memory performance after bed rest protocols. Citations are presented in the Reference section. Bottom: Summary of findings from the present study showing (A) no differences in spatial working memory behavior performance; (B) decreasing activation in some brain regions suggesting that HDBR + CO2 may reduce subjects’ ability to recruit appropriate working memory networks; (C) positive and negative brain-behavior correlations suggesting adaptive or compensatory brain response to HDBR + CO2.

中文翻译：

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在二氧化碳升高的航天模拟过程中神经工作记忆的变化：一项试点研究

前往国际空间站 (ISS) 的太空飞行任务将宇航员暴露在微重力、辐射、隔离和二氧化碳 (CO2) 升高等因素中。低头倾斜床架 (HDBR) 是一种基于地球的航天模拟，用于研究身体卸载、流体移动和其他与重力变化无关的因素。在太空中，宇航员需要使用心理旋转策略来促进他们对国际空间站环境的适应。因此，空间工作记忆对于机组人员的表现至关重要。尽管最近研究了 HDBR 对空间工作记忆的影响，但结果仍然没有定论。在这里，我们扩展了过去的工作，并检查了 HDBR 与升高的 CO2 (HDBR + CO2) 对空间工作记忆表现期间大脑激活模式的影响。此外，我们比较了 30 天 HDBR + CO2 和 70 天 HDBR 之间的大脑激活，以测试 CO2 的孤立效应。11 名受试者（6 名男性，5 名女性；平均年龄 = 34 ± 8 岁）在 HDBR + CO2 之前、期间和之后接受了六次功能性磁共振成像 (fMRI) 会议。在 HDBR + CO2 干预期间，我们观察到右侧额中回和小脑左侧区域的激活减少，随后干预后恢复。我们通过 HDBR + CO2 干预检测到大脑和行为变化斜率之间的几种相关性。例如，额叶、颞叶和顶叶区域的激活增加与更大的空间工作记忆改善有关。将 HDBR + CO2 组与我们之前 70 天 HDBR 研究的数据进行比较，我们发现 HDBR + CO2 组在干预过程中右侧海马体和左侧颞下回的激活减少更多。总之，这些发现增加了我们对 HDBR 的神经机制、二氧化碳水平升高和空间工作记忆性能与航天相关的变化的理解。图形摘要顶部：先前关于卧床休息协议后空间工作记忆性能的发现。参考文献部分提供了引文。底部：本研究的结果总结显示（A）空间工作记忆行为表现没有差异；(B) 减少某些大脑区域的激活表明 HDBR + CO2 可能会降低受试者招募适当工作记忆网络的能力；