Plant cognition

The idea of cognition in plants was first explored by Charles Darwin in the late 1800s in the book The Power of Movement in Plants, co-authored with his son Francis. Using a neurological metaphor, he described the sensitivity of plant roots in proposing that the tip of roots acts like the brain of some lower animals. This involves reacting to sensation in order to determine their next movement[5] even though plants possess neither brains nor nerves. 

Irrespective of whether this neurological metaphor is correct or, more generally, the modern application of neuroscience terminology and concepts to plants is appropriate, the Darwinian idea of the root tip of plants functioning as a "brain-like" organ (together with the so-called "root-brain hypothesis") has experienced an ongoing revival in plant physiology.[6]

While plant "neurobiology" focuses on the physiological study of plants, modern plant cognition primarily applies a behavioural/ecological approach. Today, plant cognition is emerging as a field of research directed at experimentally testing the cognitive abilities of plants, including perception, learning processes, memory and consciousness.[7] This framework holds considerable implications for the way we perceive plants as it redefines the traditionally held boundary between animals and plants.[8]

The study of plant cognition stems from the idea that plants are able to learn and adapt to their environment with only a stimulus, integration, and response system. While proven that plants do indeed lack a brain and the function of a conscious working nervous system, plants are still somehow capable of adapting to their environment and changing the integration pathway that would ultimately lead to how a plant “decides” to take response to a presented stimulus.[9] This raises issues of plant intelligence which is defined to be able to actively adapt to any stimulus presented to the species from the environment.[10] Plants are therefore clever in sensing the environmental stimulus e.g young sunflowers that face the sun for their growth.

In 2003, Anthony Trewavas led a study to see how the roots interact with one another and study their signal transduction methods. He was able to draw similarities between water stress signals in plants affecting developmental changes and signal transductions in neural networks causing responses in muscle.[17] Particularly, when plants are under water stress, there are abscisic acid dependent and independent effects on development.[18] This brings to light further possibilities of plant decision-making based on its environmental stresses. The integration of multiple chemical interactions show evidence of the complexity in these root systems.[19]

In 2012, Paco Calvo Garzón and Fred Keijzer speculated that plants exhibited structures equivalent to (1) action potentials (2) neurotransmitters and (3) synapses. Also, they stated that a large part of plant activity takes place underground, and that the notion of a 'root brain' was first mooted by Charles Darwin in 1880. Free movement was not necessarily a criterion of cognition, they held. The authors gave five conditions of minimal cognition in living beings, and concluded that 'plants are cognitive in a minimal, embodied sense that also applies to many animals and even bacteria.'[3] In 2017 biologists from University of Birmingham announced that they found a "decision-making center" in the root tip of dormant Arabidopsis seeds.[20]

In 2014, Anthony Trewavas released a book called Plant Behavior and Intelligence that highlighted a plant's cognition through its colonial-organization skills reflecting insect swarm behaviors.[21] This organizational skill reflects the plant's ability to interact with its surroundings to improve its survivability, and a plant's ability to identify exterior factors. Evidence of the plant's minimal cognition of spatial awareness can be seen in their root allocation relative to neighboring plants.[22] The organization of these roots have been found to originate from the root tip of plants.[23]

On the other hand, Dr. Crisp and his colleagues proposed a different view on plant memory in their review: plant memory could be advantageous under recurring and predictable stress; however, resetting or forgetting about the brief period of stress may be more beneficial for plants to grow as soon as the desirable condition returns.[24]

Affifi (2018) proposed an empirical approach to examining the ways plants model coordinate goal-based behaviour to environmental contingency as a way of understanding plant learning.[25] According to this author, associative learning will only demonstrate intelligence if it is seen as part of teleologically integrated activity. Otherwise, it can be reduced to mechanistic explanation.

Raja et al (2020) found that potted French bean plants, when planted 30 centimetres from a garden cane, would adjust their growth patterns to enable themselves to use the cane as a support in the future. Raja later stated that "If the movement of plants is controlled and affected by objects in their vicinity, then we are talking about more complex behaviours (rather than simple) reactions". Raja proposed that researchers should look for corresponding cognitive signatures.[26][27]

In 2017 Yokawa, K. et al. found that, when exposed to anesthetics, a number of plants lost both their autonomous and touch-induced movements. Venus flytraps no longer generate electrical signals and their traps remain open when trigger hairs were touched, and growing pea tendrils stopped their autonomous movements and were immobilized in a curled shape.[28]

The idea of plant cognition is a source of controversy.

Amadeo Alpi and 35 other scientists published an article in 2007 titled “Plant Neurobiology: No brain, No gain?” in Trends in Plant Science.[29] In this article, they argue that since there is no evidence for the presence of neurons in plants, the idea of plant neurobiology and cognition is unfounded and needs to be redefined. In response to this article, Francisco Calvo Garzón published an article in Plant Signaling and Behavior.[9] He states that, while plants do not have "neurons" as animals do, they do possess an information-processing system composed of cells. He argues that this system can be used as a basis for discussing the cognitive abilities of plants.

• Animal cognition
• Boquila trifoliolata
• Embodied cognition
• Plant perception (physiology)
• Plantoid