Structural, neural and mental underpinnings of rat ticklishness

本提案的主要目的是确定老鼠挠痒的结构、神经和心理基础。挠痒痒，一种奇特而有趣的社交接触形式，已经被哲学家和科学家讨论了两千多年。尽管历史上对挠痒痒这个话题很感兴趣，但一些基本问题仍未得到解答：为什么挠痒痒会引起笑声？为什么身体部位的挠痒程度不同？为什么我们不能给自己挠痒痒？我们之前的研究表明，躯干体感皮层第5层的活动可能足以引起大鼠的瘙痒。在这些发现的基础上，我们将牢记三个主要目标。(i)我们将利用药理学和光遗传学阻断技术进一步证实躯干体感皮层第5层含有易痒的神经基质。（ii）我们将识别介导挠痒的微电路，并试图理解为什么某些身体部位优先易痒。（iii）我们会问，从神经学的角度来看，是什么让挠痒痒变得有趣？我们将研究大鼠是否会自愿地自我管理电挠，即微刺激或体感觉皮层的光遗传激活。我们的电/光遗传脑刺激方法将允许在没有外部线索的情况下施加相同的大脑活动，在存在弱线索（静止的手）或存在强线索（假装触摸的手）的情况下。通过这种方式，拟议的实验将阐明老鼠是如何产生挠痒因子的想法的，这是一种极大地影响挠痒感觉的心理结构。

The primary objective of this proposal is to determine the structural, neural, and mental underpinnings of rat ticklishness. Tickling, a peculiar and amusing form of social touch, has been discussed by philosophers and scientists for more than two millennia. Despite a historical interest in tickling as a topic, fundamental questions remain unanswered: Why does tickling induce laughter? Why do body parts differ in ticklishness? Why can we not tickle ourselves? Our previous work suggests that activity in layer 5 of trunk somatosensory cortex might be sufficient for evoking ticklishness in rats. We will build on these findings with three main goals in mind. (i) We will further corroborate that layer 5 of trunk somatosensory cortex harbors the neural substrate of ticklishness using pharmacological and optogenetic blocking techniques. (ii) We will identify the microcircuits mediating ticklishness and attempt to understand why some body parts are preferentially ticklish. (iii) We will ask, in neural terms, what makes tickling fun? We will investigate if rats will voluntarily self-administer electric tickling, i.e. microstimulation or optogenetic activation of the somatosensory cortex. Our electrical/optogenetic brain stimulation approach will allow imposing the same brain activity without external cues, in the presence of a weak cue (a still hand) or in the presence of a strong cue (a hand pretending to touch). This way the proposed experiments will elucidate how rats generate the idea of a tickling agent, a mental construct that greatly affects ticklish sensations.