| 幸福大叔 |
2022-07-16 08:56 |
Electrical experiments with plants that count and communicate
植物有大脑活动吗?
I'm a neuroscientist, and I'm the co-founder of Backyard Brains, and our mission is to train the next generation of neuroscientists by taking graduate-level neuroscience research equipment and making it available for kids in middle schools and high schools.
00:15
And so when we go into the classroom, one way to get them thinking about the brain, which is very complex, is to ask them a very simple question about neuroscience, and that is, "What has a brain?" When we ask that, students will instantly tell you that their cat or dog has a brain, and most will say that a mouse or even a small insect has a brain, but almost nobody says that a plant or a tree or a shrub has a brain. And so when you push -- because this could actually help describe a little bit how the brain actually functions -- so you push and say, "Well, what is it that makes living things have brains versus not?" And often they'll come back with the classification that things that move tend to have brains. And that's absolutely correct. Our nervous system evolved because it is electrical. It's fast, so we can quickly respond to stimuli in the world and move if we need to. But you can go back and push back on a student, and say, "Well, you know, you say that plants don't have brains, but plants do move." Anyone who has grown a plant has noticed that the plant will move and face the sun. But they'll say, "But that's a slow movement. You know, that doesn't count. That could be a chemical process." But what about fast-moving plants?
01:30
Now, in 1760, Arthur Dobbs, the Royal Governor of North Carolina, made a pretty fascinating discovery. In the swamps behind his house, he found a plant that would spring shut every time a bug would fall in between it. He called this plant the flytrap, and within a decade, it made its way over to Europe, where eventually the great Charles Darwin got to study this plant, and this plant absolutely blew him away. He called it the most wonderful plant in the world. This is a plant that was an evolutionary wonder. This is a plant that moves quickly, which is rare, and it's carnivorous, which is also rare. And this is in the same plant. But I'm here today to tell you that's not even the coolest thing about this plant. The coolest thing is that the plant can count.
02:18
So in order to show that, we have to get some vocabulary out of the way. So I'm going to do what we do in the classroom with students. We're going to do an experiment on electrophysiology, which is the recording of the body's electrical signal, either coming from neurons or from muscles. And I'm putting some electrodes here on my wrists. As I hook them up, we're going to be able to see a signal on the screen here. And this signal may be familiar to you. It's called the EKG, or the electrocardiogram. And this is coming from neurons in my heart that are firing what's called action potentials, potential meaning voltage and action meaning it moves quickly up and down, which causes my heart to fire, which then causes the signal that you see here. And so I want you to remember the shape of what we'll be looking at right here, because this is going to be important. This is a way that the brain encodes information in the form of an action potential.
03:09
So now let's turn to some plants. So I'm going to first introduce you to the mimosa, not the drink, but the Mimosa pudica, and this is a plant that's found in Central America and South America, and it has behaviors. And the first behavior I'm going to show you is if I touch the leaves here, you get to see that the leaves tend to curl up. And then the second behavior is, if I tap the leaf, the entire branch seems to fall down. So why does it do that? It's not really known to science. One of the reasons why could be that it scares away insects or it looks less appealing to herbivores. But how does it do that? Now, that's interesting. We can do an experiment to find out.
03:52
So what we're going to do now, just like I recorded the electrical potential from my body, we're going to record the electrical potential from this plant, this mimosa. And so what we're going to do is I've got a wire wrapped around the stem, and I've got the ground electrode where? In the ground. It's an electrical engineering joke. Alright.
04:13 (Laughter)
04:14
Alright. So I'm going to go ahead and tap the leaf here, and I want you to look at the electrical recording that we're going to see inside the plant. Whoa. It is so big, I've got to scale it down. Alright. So what is that? That is an action potential that is happening inside the plant. Why was it happening? Because it wanted to move. Right? And so when I hit the touch receptors, it sent a voltage all the way down to the end of the stem, which caused it to move. And now, in our arms, we would move our muscles, but the plant doesn't have muscles. What it has is water inside the cells and when the voltage hits it, it opens up, releases the water, changes the shape of the cells, and the leaf falls.
04:52
OK. So here we see an action potential encoding information to move. Alright? But can it do more? So let's go to find out. We're going to go to our good friend, the Venus flytrap here, and we're going to take a look at what happens inside the leaf when a fly lands on here. So I'm going to pretend to be a fly right now. And now here's my Venus flytrap, and inside the leaf, you're going to notice that there are three little hairs here, and those are trigger hairs. And so when a fly lands -- I'm going to touch one of the hairs right now. Ready? One, two, three. What do we get? We get a beautiful action potential. However, the flytrap doesn't close. And to understand why that is, we need to know a little bit more about the behavior of the flytrap. Number one is that it takes a long time to open the traps back up -- you know, about 24 to 48 hours if there's no fly inside of it. And so it takes a lot of energy. And two, it doesn't need to eat that many flies throughout the year. Only a handful. It gets most of its energy from the sun. It's just trying to replace some nutrients in the ground with flies. And the third thing is, it only opens then closes the traps a handful of times until that trap dies. So therefore, it wants to make really darn sure that there's a meal inside of it before the flytrap snaps shut. So how does it do that? It counts the number of seconds between successive touching of those hairs. And so the idea is that there's a high probability, if there's a fly inside of there, they're going to be quick together, and so when it gets the first action potential, it starts counting, one, two, and if it gets to 20 and it doesn't fire again, then it's not going to close, but if it does it within there, then the flytrap will close.
06:33
So we're going to go back now. I'm going to touch the Venus flytrap again. I've been talking for more than 20 seconds. So we can see what happens when I touch the hair a second time. So what do we get? We get a second action potential, but again, the leaf doesn't close. So now if I go back in there and if I'm a fly moving around, I'm going to be touching the leaf a few times. I'm going to go and brush it a few times. And immediately, the flytrap closes. So here we are seeing the flytrap actually doing a computation. It's determining if there's a fly inside the trap, and then it closes.
07:08
So let's go back to our original question. Do plants have brains? Well, the answer is no. There's no brains in here. There's no axons, no neurons. It doesn't get depressed. It doesn't want to know what the Tigers' score is. It doesn't have self-actualization problems. But what it does have is something that's very similar to us, which is the ability to communicate using electricity. It just uses slightly different ions than we do, but it's actually doing the same thing. So just to show you the ubiquitous nature of these action potentials, we saw it in the Venus flytrap, we've seen an action potential in the mimosa. We've even seen an action potential in a human.
07:49
Now, this is the euro of the brain. It's the way that all information is passed. And so what we can do is we can use those action potentials to pass information between species of plants. And so this is our interspecies plant-to-plant communicator, and what we've done is we've created a brand new experiment where we're going to record the action potential from a Venus flytrap, and we're going to send it into the sensitive mimosa.
08:15
So I want you to recall what happens when we touch the leaves of the mimosa. It has touch receptors that are sending that information back down in the form of an action potential. And so what would happen if we took the action potential from the Venus flytrap and sent it into all the stems of the mimosa? We should be able to create the behavior of the mimosas without actually touching it ourselves.
08:37
And so if you'll allow me, I'm going to go ahead and trigger this mimosa right now by touching on the hairs of the Venus flytrap. So we're going to send information about touch from one plant to another.
08:54
So there you see it. So --
08:57 (Applause)
09:03
So I hope you learned a little bit, something about plants today, and not only that. You learned that plants could be used to help teach neuroscience and bring along the neurorevolution.
09:12 Thank you.
09:14 (Applause)
JIE LEI, Translator
Cissy Yun, Reviewer
我是位神经学家， Backyard Brains的联合创始人， 我们的使命是 培养下一代的神经学家， 通过将研究生运用的研究设备 融入到初高中课程中。
00:15
开始上课的时候， 我们让他们开始思考关于大脑， 这个十分复杂的物体的一个方法， 就是向他们提出一个非常简单的 关于神经科学的问题， “什么东西具有大脑“？ 当我们提问的时候， 学生们会马上告诉你 他们的猫或狗有大脑， 大多数学生会说一只老鼠 甚至一只小昆虫有大脑， 但几乎没人会说一棵植物或者树， 或者一株灌木有大脑。 所以当你进一步启发他们—— 因为这实际上可以帮助描述 大脑是如何运作的—— 所以当你继续问 “是什么让有些生物拥有大脑， 而有些则没有？” 他们往往会分类作答， 那就是移动的物体拥有大脑。 这绝对是正确的。 我们的神经系统因电流而进化。 它们速度很快， 在我们需要的情况下 使我们能快速对 外界刺激做出反应。 但是你可以引导学生逆向思维， “很好，你说植物没有大脑，” “但它们可以移动啊。” 任何养过植物的人 都会注意到植物可以移动， 并且趋光。 但他们会说， “这是一个缓慢的过程。” “这不算，那可能是一种化学过程。” 但如果是快速运动的植物呢？
01:30
在1760年，北卡罗莱纳州的 皇家总督亚瑟▪多布斯 发现一个很有趣的现象。 在他房子后面的沼泽地， 生长着一种植物，每当有虫子落在 它们的叶片之间，叶片就会闭合。 他称之为捕蝇草。 十年内，捕蝇草已经到了欧洲， 伟大的查尔斯▪达尔文 开始研究这种植物， 捕蝇草让他十分着迷。 达尔文称之为世界上最奇妙的植物。 这是一种进化奇迹。 植物可以快速运动， 非常罕见。 而且捕蝇草是 肉食性植物，同样罕见。 两种特征合二为一。 但是，今天在这里我要告诉你 这并不是捕蝇草最奇特的地方。 最奇特的是这种植物有计算能力。
02:18
为了证明这一点， 我们需要认识一些词汇。 今天我要在这里做一项 和学生们在教室里一起做的实验。 我们今天要做一个 关于电生理现象的实验， 就是记录身体中 来自神经元或肌肉的电信号。 我在手腕上贴上电极。 当我连接上之后， 我们可以看到有信号 显示在记录仪屏幕上。 这种图案你可能很熟悉。 就是所谓的心电图。 来自我心脏的神经元， 正在发射所谓的动作电位， 电位即电压，动作即意味着 它能快速上下运动， 使我的心脏跳动， 然后你就能在这儿看到电信号。 现在，你要记住你所看到的 仪器上显示的信号形状， 这是非常重要的一步。 这是大脑以动作电位 编码信息的一种方式。
03:09
现在，我们来关注一些植物。 第一步，我将向你介绍含羞草， 不是那种饮料，是含羞草植物， 这种植物发现于 美州中部和南部地区， 这种植物具有行为。 我将向你展示 含羞草的第一种行为， 碰到它这里的叶片， 你会看到叶子蜷起来了。 第二种行为是， 如果我轻点叶子， 整个枝条似乎都垂下了。 问题来了，含羞草 为什么要这样呢？ 这在科学上仍然未知。 其中原因之一 可能是为了吓跑昆虫， 或者看起来不太吸引食草动物。 但它是怎么做到的呢？ 这就非常有趣了。 我们可以做个实验了解一下。
03:52
我们要做的是， 就像我记录我身体的电流一样， 我们将记录含羞草的电流数据。 我们要用一根电线 缠绕在含羞草的茎上， 我把接地线放哪了？ 在地上呢，这是个电气工程玩笑。
04:13（笑声）
04:14
好了，接下来 我要继续轻点叶子了， 你将会看到在植物内部 记录下的电子数据。 哇，波动很强烈，让我把 整个信号调整到屏幕以内。 好了，那是什么呢？ 那是植物内部发生的一种动作电位。 为什么会发生这样的情况呢？ 因为它（含羞草）想要移动，对吗？ 所以当我碰到传感器（枝叶）的时候， 它将电流传送到枝叶末端， 这就导致它垂落枝条。 我们可以让手臂上的 肌肉动起来， 但植物并没有肌肉。 植物的细胞内充满液体， 当电流传导时，细胞打开，释放液体， 并改变细胞的形态，然后枝叶垂落。
04:52
好的，我们看到了动作电位 通过编码信息来运动。 但是，植物可以做更多的事情吗？ 我们再来深入了解一下。 现在请出我们的好朋友， 维纳斯捕蝇草， 当苍蝇落在叶子中间， 我们来观察会发生什么。 现在我要假装是一只苍蝇。 这是维纳斯捕蝇草， 在叶片内侧，你会注意到 有三根毛发，这是它的触发毛。 所以当苍蝇降落的时候—— 我要触碰触发毛了。 准备好了吗？1,2,3。 看，我们得到了一条优美的 动作电位图。 然而，捕蝇草叶片并没有闭合。 为了了解为什么会这样， 我们需要了解一些捕蝇草的行为。 第一条，它需要很长时间 来打开陷阱（叶片）—— 如果没有苍蝇在里面， 大概需要24到48小时。 所以需要大量的能量。 第二条，它全年 不需要吃太多苍蝇。 几只就够了，它通过 阳光来摄取大部分的能量。 它只是想用苍蝇替代一些 从地下获得的养分。 第三条， 直到叶片枯萎， 陷阱只能开合几次。 因此，它要确保捕虫叶闭合前， 里面一定有顿美餐。 所以，它怎么做到的呢？ 捕蝇草是通过 计算连续触碰触发毛的秒数。 所以，我们的想法是 有一个高的概率， 如果里面有只苍蝇，可以视为触碰， 当捕蝇草接收第一次的信号时， 开始计数，1，2， 如果计数到20又没有中断， 它不会闭合捕虫叶， 但如果苍蝇依然在里面， 陷阱就闭合了。
06:32
我们继续实验。 我将再次触碰维纳斯捕蝇草。 我已经说了超过20秒话了。 让我们来看看再次 碰到触发毛会发生什么。 我们得到了什么？ 第二次动作电位， 但是，捕虫叶仍然没有闭合。 现在，我再回到那里， 假装我是一只苍蝇到处移动， 我将触碰叶片几次。 刷几下。 捕蝇草 立刻闭合了。 我们看到捕蝇草实际上是在计算。 这取决于苍蝇是否在陷阱里， 然后就闭合了。
07:08
那么，让我们回到最初的问题上。 植物有大脑吗？ 答案是否定的。 植物并没有大脑。 没有轴突，没有神经元。 它不会郁郁寡欢。 不会考虑底特律 老虎队的得分是多少。 没有自我实现的问题。 但它们的行为与我们如此相似， 是使用生物电交流的能力。 它仅是使用了 与我们稍微不用的离子， 但实际上做的是同样的事情。 这个实验是为了展示， 动作电位的自然普遍性， 我们能在维纳斯捕蝇草上看到， 在含羞草上看到， 在人类身上也能看到。
07:49
这就是大脑的神经。 所有信息的传递方式。 所以我们能做的就是 利用这些动作电位 在不同种类的植物间 传递信息。 所以，这就是植物与植物间的交流， 我们所做的是创造出了 一种全新的实验， 从维纳斯捕蝇草中记录动作电位， 然后传送到敏感的含羞草中。
08:15
所以，我想要你回想一下， 当我们触碰含羞草叶片的 时候发生了什么。 它拥有以动作电位的形式 传递信息的传感器。 所以，如果我们 从维纳斯捕蝇草中捕捉到 电动电位，并将之发送到 含羞草的所有茎叶中，会发生什么？ 我们应该可以引发 含羞草的收缩行为， 而不需要亲自触碰。
08:37
所以，让我来展示， 我将继续通过触碰 捕蝇草的触发毛来 触发含羞草的收缩行为。 我们要将触碰信息 从一株植物传递到另一株植物上。
08:54
看到（含羞草枝叶收缩）了吧。 那么——
08:57
（掌声）
09:03
希望你今天能学到 一些关于植物的知识， 而且不仅仅如此。 你了解到植物可以 用来帮助神经教学， 并带来神经学革命。
09:12 谢谢。
09:13 （掌声）
https://www.ted.com/talks/greg_gage_electrical_experiments_with_plants_that_count_and_communicate/transcript
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