Plant neurobiology is a growing field of science that explores the ways that plants may perceive their environment and alter their morphology and physiology accordingly. It’s sparked some blowback as there are others who argue that growing with style isn't akin to cognition or consciousness, but what about unconsciousness?
Plants don’t sleep in the same way that humans do, but like humans, they are less active at night. They possess their own kind of circadian rhythms, internal clocks that use environmental and chemical cues to distinguish night from day, and like some animals, they can wake up with the Sun.
Plants waking up have even been seen from space, thanks to NASA’s Ecosystem Spaceborne Thermal Radiometer on Space Station (ECOSTRESS), an instrument that’s stuck on the International Space Station (ISS). ECOSTRESS can monitor the health of vegetation down on Earth by taking its temperature and keeping track of processes like evapotranspiration in which plants effectively “sweat” excess water to cool down.
Images captured from space in 2019 showed how plants near Lake Superior, US, were able to show how plant activity picks up throughout the morning as plants “wake up”. Scientists on board the ISS found that plants nearest the water’s edge were the early risers, showing signs of activity earlier than plants that were further away.
So, if plants can wake up, can we put them to sleep? That’s something botanist Stefano Mancuso has been looking into at The International Laboratory of Plant Neurobiology.
The curious observation that fuels Mancuso’s pursuit of evidence for plant intelligence was a root growing around an obstacle. Filming the movement revealed that the plant didn’t need to touch the obstacle before it started mapping out a better direction of growth, so how did it know to move?
Plant movement sounds strange but is a lot more common than most people realize, it’s just happening at a speed that makes for boring viewing (unless you look at the extremes of sensitive plants and Venus fly traps). David Attenborough’s Green Planet was able to demonstrate what most of us never see, showing the way that plants can grapple for sunlight, sometimes using what humans might perceive as dirty tactics to eradicate the competition.
It's observations like these that have pushed Mancuso to ask questions about the possibility of plant consciousness, something he says is hard to prove or disprove without a clear definition of what that means.
“It’s incredibly difficult to talk about consciousness, first because we actually don’t know what consciousness is, even in our case,” he told The Guardian. “But there is an approach to talking about it as a real biological feature: consciousness is something that we all have, except when we are sleeping very deeply or when we are under anaesthesia.”
“My approach to studying consciousness in plants was similar. I started by seeing if they were sensitive to anaesthetics and found that you can anaesthetise all plants by using the same anaesthetics that work in humans. This is extremely fascinating. We were thinking that consciousness was something related to the brain, but I think that both consciousness and intelligence are more embodied, relating to the entire body.”
As for putting plants “to sleep”, Mancuso’s team believes that they may have achieved just that by the end of 2023. Now, who’s going to option our Pixar script for The Very Sleepy Corpse Flower?