It’s long been assumed that for an organism to learn, remember or draw conclusions, it needs a brain. But mounting evidence, including a recent Cognitive Science study, challenges that assumption, suggesting that neurons might not be necessary for complex information processing.
The new study, authored by William & Mary Professor of Psychology Peter Vishton and his former student Paige Bartosh ’25, indicates that plants may be able to count. Well … not in the way that humans can. But it appears that Mimosa pudica plants can somehow “keep track of the number of events in their environment,” said Vishton.
To the researchers’ knowledge, this is the first evidence that plants can enumerate — the ability to distinguish between and track discrete events.
Plants may be “smarter” than people think
Commonly known as the shy plant or touch-me-not plant, Mimosa pudica has delicate, frond-like leaves that fold inward when touched or shaken. They also close at night and reopen with the rising of the sun — a type of movement called nyctinasty.
In a humid tent inside a windowless room in W&M’s Integrated Science Center, Vishton and Bartosh exposed these plants to cycles of light and dark and observed a curious change in their movement.
“In the first phase of our experiment, we used a 24-hour cycle. On days one and two, the plants were exposed to 12 hours of darkness and 12 hours of light. On day three, the lights remained off,” Vishton explained.
After around five repetitions of this cycle, the plants demonstrated increased movement in the “pre-dawn” hours on days when light could be anticipated, but not on the third day of total darkness.
“This seems to suggest that the plants were able to ‘learn,’ for lack of a better word, this three-day cycle and shift their movement in response,” said Vishton.
Modeling this shift yielded a logarithmic curve, meaning the plants’ movement changed rapidly at first before gradually stabilizing into a consistent pattern.
“This is the same pattern we see all the time in animal learning,” said Vishton. “For example, if you are teaching a rat to perform a series of actions in a certain order, you would expect to see a period of time when they’re figuring out the sequence and then a gradual increase in their ability to predict the pattern.”
But Vishton wanted to investigate another possible explanation for the plants’ movement. Instead of tracking a number, they could be tracking time.
“It’s well established that many plants move in alignment with a 24-hour circadian rhythm, opening up in anticipation of the sun,” said Vishton. “While no evidence suggests plants can track a 72-hour cycle — the duration of the three-day pattern in our study — we wanted to test that possibility.”
Decreasing the length of the days from 24 to 20 hours, Vishton and Bartosh observed an almost immediate shift in plant movement, following this adjusted pattern of light and dark. To further strengthen the evidence that the plants were moving based on enumeration, they performed a final experiment in which each three-day cycle was assigned a random length, ranging from 10 hours (five hours of light and five of dark) to 32 hours.
Interestingly, on days shorter and longer than 12 to 24 hours, the pattern broke down. Vishton thinks this implies a minimum exposure window for plants to process the light-dark pattern and a maximum memory limit after which they “forget” the pattern.
But within the 12 to 24-hour range, the plants continued to exhibit more movement on days when light could be anticipated than on dark days.
“The simplest explanation for this result is that these plants are tracking the number of events that take place,” said Vishton. “Not simply responding to time.”
A new type of intelligence
If this result is borne out by future experiments, it provides evidence for a whole different type of information processing.
“Every theory I’ve ever read on memory and decision making always involves neurons,” said Vishton. “Big surprise, plants don’t have those. And yet it looks like they can perform cognitive-like functions. Just not cognitively, per se.”
If plants can encode complex functions like enumeration, maybe other non-neuronal tissues can too.
“There are lots of cells in animals and humans that aren’t neurons. And we just assume they’re not involved in learning,” said Vishton. “But maybe they could be. Maybe learning is present in every cell. We’ve just never really studied it before.”
How exactly this non-neuronal intelligence is learned, stored and called upon is a question for future experiments.
“As a developmental psychologist, I’m interested in characterizing behavior,” said Vishton. “I’m hoping the chemists and biologists of this world can ask more mechanistic questions to understand how this is actually happening. With more research on both fronts, I’m very excited to see where this field of study is headed.”
Future applications for this research could include biologically based computational devices, plant-based sensors and even methods to help humans “unlearn” addictive behaviors on a cellular level.
By hinting at a new type of intelligence, this research adds to the body of evidence challenging the distinction between plant and animal.
“Typically, we don’t conceptualize plants as thinking, behaving creatures, right? We think of them as reflexive objects that are responding to stimuli in a simple way,” said Vishton. “But, at least to me, our results suggest that there might not be this boundary between the animal and the plant kingdom — or it might be a lot more porous than we think.”
Read the full open-access publication of Vishton and Bartosh’s research at Cognitive Science.
Catherine Tyson, Communications Specialist