Laboratory of Sleep Neurobiology, Department of Physiology, School of Medicine, Universidad de la República, Montevideo, Uruguay.
Consciousness and Cognition Laboratory, Department of Psychology, University of Cambridge, Cambridge, UK.
Eur J Neurosci. 2022 Mar;55(6):1584-1600. doi: 10.1111/ejn.15646. Epub 2022 Mar 19.
There is increasing evidence that the level of consciousness can be captured by neural informational complexity: for instance, complexity, as measured by the Lempel Ziv (LZ) compression algorithm, decreases during anaesthesia and non-rapid eye movement (NREM) sleep in humans and rats, when compared with LZ in awake and REM sleep. In contrast, LZ is higher in humans under the effect of psychedelics, including subanaesthetic doses of ketamine. However, it is both unclear how this result would be modulated by varying ketamine doses, and whether it would extend to other species. Here, we studied LZ with and without auditory stimulation during wakefulness and different sleep stages in five cats implanted with intracranial electrodes, as well as under subanaesthetic doses of ketamine (5, 10, and 15 mg/kg i.m.). In line with previous results, LZ was lowest in NREM sleep, but similar in REM and wakefulness. Furthermore, we found an inverted U-shaped curve following different levels of ketamine doses in a subset of electrodes, primarily in prefrontal cortex. However, it is worth noting that the variability in the ketamine dose-response curve across cats and cortices was larger than that in the sleep-stage data, highlighting the differential local dynamics created by two different ways of modulating conscious state. These results replicate previous findings, both in humans and other species, demonstrating that neural complexity is highly sensitive to capture state changes between wake and sleep stages while adding a local cortical description. Finally, this study describes the differential effects of ketamine doses, replicating a rise in complexity for low doses, and further fall as doses approach anaesthetic levels in a differential manner depending on the cortex.
越来越多的证据表明，意识水平可以通过神经信息复杂性来捕捉：例如，与清醒和快速眼动 (REM) 睡眠相比，在人类和大鼠中，麻醉和非快速眼动 (NREM) 睡眠期间，复杂性（通过 Lempel Ziv (LZ) 压缩算法测量）会降低。相比之下，在人类中，在致幻剂的作用下，包括亚麻醉剂量的氯胺酮，LZ 更高。然而，目前尚不清楚这种结果如何受到不同氯胺酮剂量的调节，以及它是否会扩展到其他物种。在这里，我们研究了五只植入颅内电极的猫在清醒和不同睡眠阶段以及亚麻醉剂量氯胺酮（5、10 和 15 mg/kg i.m.）下的 LZ。与之前的结果一致，LZ 在 NREM 睡眠中最低，但 REM 和清醒时相似。此外，我们在一组电极中发现了不同氯胺酮剂量下的倒 U 形曲线，主要在前额叶皮层。然而，值得注意的是，在不同猫和皮层中，氯胺酮剂量反应曲线的变异性大于睡眠阶段数据的变异性，这突出了两种不同方式调节意识状态所产生的局部动态的差异。这些结果复制了之前在人类和其他物种中的发现，表明神经复杂性对清醒和睡眠阶段之间的状态变化非常敏感，同时增加了局部皮质描述。最后，这项研究描述了氯胺酮剂量的差异效应，复制了低剂量时复杂性的增加，并且随着剂量接近麻醉水平，根据皮层的不同，进一步下降。
