Alterations in brain rheology are increasingly recognized as a diagnostic marker for various neurological conditions. Magnetic resonance elastography now allows us to assess brain rheology repeatably, reproducibly, and non-invasively in vivo. Recent elastography studies suggest that brain stiffness decreases one percent per year during normal aging, and is significantly reduced in Alzheimer's disease and multiple sclerosis. While existing studies successfully compare brain stiffnesses across different populations, they fail to provide insight into changes within the same brain. Here we characterize rheological alterations in one and the same brain under extreme metabolic changes: alive and dead. Strikingly, the storage and loss moduli of the cerebrum increased by 26% and 60% within only three minutes post mortem and continued to increase by 40% and 103% within 45 minutes. Immediate post mortem stiffening displayed pronounced regional variations; it was largest in the corpus callosum and smallest in the brainstem. We postulate that post mortem stiffening is a manifestation of alterations in polarization, oxidation, perfusion, and metabolism immediately after death. Our results suggest that the stiffness of our brain–unlike any other organ–is a dynamic property that is highly sensitive to the metabolic environment. Our findings emphasize the importance of characterizing brain tissue in vivo and question the relevance of ex vivo brain tissue testing as a whole. Knowing the true stiffness of the living brain has important consequences in diagnosing neurological conditions, planning neurosurgical procedures, and modeling the brain's response to high impact loading.

脑流变学的改变越来越被认为是各种神经系统疾病的诊断标志物。磁共振弹性成像现在使我们能够在体内以可重复、可重复和无创的方式评估脑流变学。最近的弹性成像研究表明，大脑僵硬在正常衰老过程中每年会降低 1%，而在阿尔茨海默病和多发性硬化症中则显着降低。虽然现有研究成功地比较了不同人群的大脑硬度，但它们未能深入了解同一大脑内的变化。在这里，我们描述了在极端代谢变化下同一个大脑中的流变学改变：生与死。引人注目的是，死后仅 3 分钟，大脑的储存和损失模量就增加了 26% 和 60%，并在 45 分钟内继续增加了 40% 和 103%。立即尸检僵硬显示出明显的区域差异；它在胼胝体中最大，在脑干中最小。我们假设死后僵硬是死后极化、氧化、灌注和新陈代谢立即发生变化的表现。我们的研究结果表明，与任何其他器官不同，我们大脑的刚度是一种动态特性，对代谢环境高度敏感。我们的研究结果强调了在体内表征脑组织的重要性，并质疑整个体外脑组织测试的相关性。