Mushroom Minds

29th September, 2022

Is there such thing as fungal consciousness? In this blog post, Nicholas P. Money discusses the possibility, debunks myths, and puts the story straight.

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One of the most thought-provoking issues to have arisen in mycology recently is the question of fungal consciousness. This originated with the publication of some fascinating experiments on mushroom colonies or mycelia that revealed a simple form of memory.[1] Before we consider the implications of this research, it is useful to think about the mushroom life cycle. Mushrooms are fruit bodies or sex organs produced by colonies or mycelia of fungi that grow in soil and decompose plant tissues. Mycelia are multicellular feeding structures composed of branching networks of filamentous cells called hyphae that grow at their tips. Once the mushroom has emerged and pumped itself up into its mature form, it begins releasing spores when the air between its gills is sufficiently humid. Spore release is an automatic mechanism that does not require any decision-making by the fungus. All of the ‘thinking’ goes on in the mycelium before mushroom formation, as the colony explores its surroundings, competes with other fungi for food, rebuffs predators, and searches for a mate.

Thinking is a loaded term, of course, but the recent work on mycelia suggests that something of the sort is going in the sense that the fungus remembers where it found food in one trial and searches for food in the same place in a second challenge. The experiments are performed on mycelia living in little blocks of wood that grow from the same side of the block from which they find food in one experiment to the next. The fungi appear to be expressing an inbuilt system for spatial navigation and a capacity for memory, neither of which have been recognized previously.

The responsiveness of the mycelium lies in the behavior of its individual hyphae. These cells operate as biosensors that communicate changes in the local environment such as the sudden pulse in soil nutrient levels when the leaves of deciduous trees fall in temperate forests. Hyphae extend at their tips and adjust their rate and direction of growth according to the availability of water and nutrients, temperature, physical obstacles in their paths, and other environmental variables. Applying more liberal definitions of the terms developed for animal cognition, these expressions of cellular sensitivity and responsiveness are consistent with a very primitive form of self-awareness. Philosopher Rupert Glasgow has described this level of consciousness in terms of minimal selfhood: “While minimal selfhood need not in itself imply consciousness, it provides the foundation for its possible appearance.”[2]

Each hypha branches as the mycelium expands, resulting in an exponential increase in the number of growing tips. This developmental process allows the fungus to explore every scrap of its immediate environment as it grows as a widening circle on a flat surface or as a fat disc in three dimensions when it sinks into soil or rotting wood. Like a network of nerve cells, a mycelium is greater than the sum of its hyphal parts. It is capable of integrating information from multiple sources and reacting as an integrated multicellular organism rather than lots of independent filaments. We see this in mycelia that redistribute resources from locations that have a rich supply of nutrients to other parts of the colony that are starving. The mechanism that underlies this transfer of energy is unknown. It may be a simple diffusive process, whereby a gradient in resources dissipates as long as an open fluid pathway is maintained from hypha to hypha. This is another automatic process, like spore release, that is primed by development and does not involve any decision-making by the fungus. But greater control may come into play here with the leaner part of the colony making a specific request for food, signaling to the adjacent hyphae that it is running out of energy. Mycologists need to design some clever experiments to distinguish between these possibilities.

There is a fine line between sensitivity and consciousness, and it is easy to mistake a purely physical reaction of an organism with something more intentional. Part of the difference lies in the degree to which the organism has options, which is why the feeding experiments are so interesting. The fungus shows a bias toward repeating the behavior that led it to find food in the first instance, but it does not make the correct decision in every trial. This stochastic behavior is critical in evaluating the presence of a simple form of consciousness.

The transfer of information across the mycelium could take place through the slow diffusion of signaling molecules from hypha to hypha or, more swiftly, via the distribution of chemical signals through the active flow of the fluid cytoplasm inside the hyphae. Measurements show that the flow of cytoplasm can move organelles through the mycelium at a rate of a few millimeters per minute, which means that a signal could be transmitted from one side of a one meter-diameter colony to the other in a few hours. This signaling process is perfectly attuned to the needs of a fungus whose hyphae extend at a rate of a few millimeters per hour. Signaling through the propagation of changes in the voltage across the fungal membrane is another plausible mechanism that is analogous to the transfer of nerve impulses in animals. Waves of electrical activity analogous to the action potentials in nerves have been recorded in fungi. These are slow pulses in voltage, lasting for 5-8 minutes rather than the millisecond duration of action potentials in nerves, but it is plausible that they provide useful information for the fungus as it continues to expand.[3]

Published estimates of the density of hyphae in grassland suggest that there can be between 10 billion and 1 trillion hyphae in one cubic meter of soil and mathematical models raise the theoretical maximum mycelial density to 130 trillion hyphal tips per cubic meter of straw or sawdust in cultivation. These numbers have encouraged comparisons with the density of neurons in the human brain. Each cubic centimeter or milliliter of brain tissue contains 68 million neurons, which is similar to the maximum number of hyphae that can be packed into the same volume of soil. Beyond the raw number of cells, nervous systems amplify their processing power through the formation of synapses that allow each nerve cell to interact with thousands of neighbors. The closest thing to synapses in fungi are tubes that allow cellular materials to flow between adjacent hyphae. We do not know how numerous these connections are in nature, but they do not come close to the connectivity of synapses.

Despite the incredible numbers of hyphae, the potential for communication is probably limited to the slow passage of chemical signals and the fungus is unlikely to be relaying anything other than ‘Food here’, ‘Send me some food’, ‘Will you mate with me?’, and ‘I have been punctured by a nematode worm’. Using this limited conversational repertoire, the mycelium is able to redistribute resources within the mycelium, find a mate, respond to stress, and shuttle nutrients between plants in the case of mycorrhizal fungi. This may qualify as consciousness and although the processing power of a brain is elevated by the synaptic connections that allow each never cell to interact with thousands of neighbors, the individual messages are probably quite similar. Consciousness hinges on universal demands of life and we have a lot to learn by remembering that we are doing the same thing as a mushroom colony searching for decomposing roots when we are making our way along the aisles in a supermarket.

– Nicholas P. Money

Nicholas P. Money is Professor of Biology and Western Program Director at Miami University in Oxford, Ohio. He is the author of popular science books on fungi and other microorganisms including, The Amoeba in the Room: Lives of the Microbes (2014), and The Selfish Ape: Human Nature and Our Path to Extinction (Reaktion, 2019).

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[1] Yu Fukasawa, Melanie Savoury, and Lynne Boddy, ‘Ecological Memory and Relocation Decisions in Fungal Networks: Responses to Quantity and Location of New Resources’, ISME Journal 14 (2020), pp. 380-88.

[2] Rupert D. V. Glasgow, Minimal Selfhood and the Origins of Consciousness (Würzburg, Germany: Würzburg University Press, 2018), p. 13.

[3] It is important to repudiate the silliness promoted by a few mycological enthusiasts who miscast the fungi as the supernatural guardians of the planet. Claims of an inner language of electrical spikes in mushroom mycelia have no more substance than the fact that weak voltages can be tapped from fruits and vegetables to power LED bulbs. The study of fungal behavior is too interesting to be derailed by this twaddle.