The periaqueductal gray (PAG) is a small midbrain structure that surrounds the cerebral aqueduct, regulates brain–body communication, and is often studied for its role in "fight-or-flight" and "freezing" responses to threat. We used ultra-high-field 7 T fMRI to resolve the PAG in humans and distinguish it from the cerebral aqueduct, examining its in vivo function during a working memory task (N = 87). Both mild and moderate cognitive demands elicited spatially similar patterns of whole-brain blood oxygenation level-dependent (BOLD) response, and moderate cognitive demand elicited widespread BOLD increases above baseline in the brainstem. Notably, these brainstem increases were not significantly greater than those in the mild demand condition, suggesting that a subthreshold brainstem BOLD increase occurred for mild cognitive demand as well. Subject-specific masks were group aligned to examine PAG response. In PAG, both mild and moderate demands elicited a well-defined response in ventrolateral PAG, a region thought to be functionally related to anticipated painful threat in humans and nonhuman animals—yet, the present task posed only the most minimal (if any) "threat," with the cognitive tasks used being approximately as challenging as remembering a phone number. These findings suggest that the PAG may play a more general role in visceromotor regulation, even in the absence of threat.

导水管周围灰质（PAG）是一种小型中脑结构，围绕脑导水管，调节大脑与身体的交流，并且经常因其在“战斗或逃跑”和“冻结”威胁反应中的作用而被研究。我们使用超高场 7 T fMRI 解析人类 PAG，并将其与脑导水管区分开来，检查其在工作记忆任务期间的体内功能 ( N = 87)。轻度和中度认知需求都会引发空间相似的全脑血氧水平依赖性（BOLD）反应模式，而中度认知需求会引发脑干中广泛的 BOLD 增加至基线以上。值得注意的是，这些脑干的增加并不显着大于轻度需求条件下的脑干增加，这表明轻度认知需求也发生了阈下脑干的大胆增加。将特定受试者的掩模进行分组以检查 PAG 反应。在 PAG 中，轻度和中度的需求都会在腹外侧 PAG 中引起明确的反应，该区域被认为在功能上与人类和非人类动物的预期疼痛威胁相关 - 然而，目前的任务仅提出了最小的（如果有的话）“威胁”，所使用的认知任务大约与记住电话号码一样具有挑战性。这些发现表明，即使没有威胁，PAG 也可能在内脏运动调节中发挥更普遍的作用。