Their findings make it extremely unlikely that plants, lacking any anatomical structures remotely comparable to the complexity of the threshold brain, possess consciousness.

Recent results of neuroscientist Todd E. Feinberg and evolutionary biologist Jon M. Mallatt on the minimum brain structures and functions required for consciousness in animals have implications for plants.

Proponents of plant consciousness have consistently glossed over the unique and remarkable degree of structural, organizational, and functional complexity that the animal brain had to evolve before consciousness could emerge.

Although ‘plant neurobiologists’ have claimed that plants possess many of the same mental features as animals, such as consciousness, cognition, intentionality, emotions, and the ability to feel pain, the evidence for these abilities in plants is highly problematical.

In claiming that plants have consciousness, ‘plant neurobiologists’ have consistently glossed over the remarkable degree of structural and functional complexity that the brain had to evolve for consciousness to emerge. Here, we outline a new hypothesis proposed by Feinberg and Mallat for the evolution of consciousness in animals. Based on a survey of the brain anatomy, functional complexity, and behaviors of a broad spectrum of animals, criteria were established for the emergence of consciousness. The only animals that satisfied these criteria were the vertebrates (including fish), arthropods (e.g., insects, crabs), and cephalopods (e.g., octopuses, squids). In light of Feinberg and Mallat’s analysis, we consider the likelihood that plants, with their relative organizational simplicity and lack of neurons and brains, have consciousness to be effectively nil.

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Glossary

an electrical impulse indicating that a cell (nerve cell, sensory cell, or muscle cell) has been activated. Action potentials of a given cell type have a stereotypic waveform and can propagate to other cells or organs at velocities between 0.5 and 100 m/s.

relating to, arising from, or influencing feelings or emotions.

the ‘corpus amygdaloideum’ or almond-shaped nucleus is a part of the mammalian brain located deep within both temporal lobes (the lateral to bottom portion of the brain). The amygdala is strongly involved in processing adverse stimuli and emotions such as fear.

a common name for drugs reducing awareness or sensation. Anesthetics cover a broad range of substances. Local anesthetics prevent signal transduction from a specific area (e.g., a finger) to the spinal cord and allow operating on a fully conscious patient. General anesthetics leave the patient unconscious and are used for more invasive procedures.

a class of plant hormones, produced mainly in the shoot tip, that promote cell division, cell elongation, and play an important role in coordinating plant development and behavioral responses; can be polarly transported cell to cell throughout the plant via specialized membrane proteins.

a section of the vertebrate’s nervous system at the interface between the brain and the spinal cord. The brainstem contains critical areas such as the centers for breathing or for regulation of heartbeat and blood pressure, as well as networks mediating arousal reactions (called the ‘reticular formation’).

an evolutionary trend in which the mouth, sense organs, and nerve ganglia become concentrated at the anterior end of the organism to produce the head.

a type of learning in which a stimulus that evokes a response is associated with a second stimulus that normally does not evoke the response, such that the second stimulus acquires the ability to evoke the response.

the frontal part of the neocortex contains several areas with different functional specializations. Major parts are involved in the preparation and execution of movements while other, even more frontal parts are required for decision making and cognitive control of spontaneous impulses.

a cluster of neurons that provides relay points and connections between different neurological structures in the body.

the most basic type of learning in which a behavioral response declines with repeated stimulation, and the decline is not caused by sensory or motor fatigue.

a group of neuronal networks or nuclei located below the thalamus, close to the base of the middle portion of the vertebrate’s brain. It is involved in homeostatic reactions such as release of hormones, sleep-wake-cycle, stress reactions, and food intake.

a section of the lateral mammalian brain hemispheres located in a deep indentation or furrow. The insula is involved in multiple sensory and emotional functions which are not yet fully understood.

the information processing cell of the nervous system that uses action potentials to send signals along the length of the cell toward the synapse, which communicates the signal to a neighboring neuron via synaptic vesicles.

a chemical that is released by presynaptic vesicles upon stimulation and then activates postsynaptic receptors.

a compact cluster of neurons deep in the brain.

an unpleasant sensation that can range from mild, localized discomfort to agony. Pain has both physical and emotional components. The physical part of pain results from the stimulation of pain receptors (nociceptors), which transmit electrical signals to the spinal cord and the brain.

a membranous vesicle containing neurotransmitters, located in the presynaptic component of a synapse, that is, in the neuronal compartment that releases the neurotransmitters in response to an action potential.

sensory consciousness, the basic ability to have subjective experiences, ‘something it is like to be’.

the part of the mammalian brain hemispheres receiving sensory signals from the body surface such as pressure, temperature, or damaging, painful stimuli.