Pavlov's Plants? Not So Fast. Kasey Markel (Plant Biology, University of California, Davis, Davis, CA ) C16
Plant intelligence, consciousness, and neurobiology have been hotly debated for the last decade. A concrete experimental finding at the center of the debate is the matter of plant learning, with some claiming plants can learn via associative or Pavlovian conditioning. The most convincing experimental demonstration of learning in plants comes from Gagliano et al's 2016 paper "Learning by association in plants". Associative learning has long been considered a behavior performed only by animals, making this claim particularly newsworthy and interesting. The experiment is based on phototropism, a well-known phenomenon in which plants grow towards light. Blue light was therefore suitable to use as an unconditioned stimulus. Wind generated by a 35 mm fan was shown to not influence plant growth direction in the absence of training, and was used as the conditioned stimulus. In the experiment, plants were trained in Y-shaped mazes for three days with fans and lights attached at the top of the maze. Training consisted of wind consistently preceding light from either the same or the opposite arm of the maze. When plant growth forced a decision between the two arms of the maze, fans alone were able to influence growth direction, directing it away from the phototropic default. Importantly, some plants were trained to grow towards the fan and others to grow away, demonstrating the flexibility of associative learning. However, a replication of their protocol failed to demonstrate the same result, calling for further verification and study before mainstream acceptance of this paradigm-shifting phenomenon. This replication attempt used a larger sample size, additional controls, and fully blinded analysis. These experiments require little technical expertise and fairly accessible equipment to perform, and are therefore accessible to replication attempts by anyone interested in learning outside the animal kingdom.