Mind-wandering has become a captivating topic for cognitive neuroscientists. By now, it is reasonably well described in terms of its phenomenology and the large-scale neural networks that support it. However, we know very little about what neurobiological mechanisms trigger a mind-wandering episode and sustain the mind-wandering brain state. Here, we focus on the role of ascending neuromodulatory systems (i.e. acetylcholine, noradrenaline, serotonin and dopamine) in shaping mind-wandering. We advance the hypothesis that the hippocampal sharp wave-ripple (SWR) is a compelling candidate for a brain state that can trigger mind-wandering episodes. This hippocampal rhythm, which occurs spontaneously in quiescent behavioural states, is capable of propagating widespread activity in the default network and is functionally associated with recollective, associative, imagination and simulation processes. The occurrence of the SWR is heavily dependent on hippocampal neuromodulatory tone. We describe how the interplay of neuromodulators may promote the hippocampal SWR and trigger mind-wandering episodes. We then identify the global neuromodulatory signatures that shape the evolution of the mind-wandering brain state. Under our proposed framework, mind-wandering emerges due to the interplay between neuromodulatory systems that influence the transitions between brain states, which either facilitate, or impede, a wandering mind.

This article is part of the theme issue ‘Offline perception: voluntary and spontaneous perceptual experiences without matching external stimulation'.

走神已经成为认知神经科学家的一个迷人话题。到目前为止，它的现象学和支持它的大规模神经网络已经得到了相当好的描述。然而，我们对哪些神经生物学机制会触发走神发作并维持走神大脑状态知之甚少。在这里，我们关注上行神经调节系统（即乙酰胆碱、去甲肾上腺素、5-羟色胺和多巴胺）在塑造走神中的作用。我们提出了这样一个假设，即海马尖波波纹 (SWR) 是一种令人信服的候选大脑状态，可以触发走神发作。这种海马节律在静止行为状态下自发发生，能够在默认网络中传播广泛的活动，并且在功能上与回忆、联想、想象和模拟过程。SWR 的发生在很大程度上取决于海马神经调节张力。我们描述了神经调节剂的相互作用如何促进海马 SWR 并引发走神发作。然后，我们确定了塑造走神大脑状态演变的全局神经调节特征。在我们提出的框架下，由于影响大脑状态之间转换的神经调节系统之间的相互作用而出现了走神，这促进或阻碍了走神。然后，我们确定了塑造走神大脑状态演变的全局神经调节特征。在我们提出的框架下，由于影响大脑状态之间转换的神经调节系统之间的相互作用而出现了走神，这会促进或阻碍走神。然后，我们确定了塑造走神大脑状态演变的全局神经调节特征。在我们提出的框架下，由于影响大脑状态之间转换的神经调节系统之间的相互作用而出现了走神，这会促进或阻碍走神。

这篇文章是主题问题“离线感知：没有匹配外部刺激的自愿和自发的感知体验”的一部分。