Jul 12, 2025 06:10 PM
https://aeon.co/essays/what-can-slime-mo...cal-memory
EXCERPTS: . . . The differences between P polycephalum and humans may seem vast, but slime mould can reveal a remarkable amount about various aspects of how we remember. While many people might assume that our memories are primarily stored within our brains, some philosophers like myself argue that – along with some other aspects of cognition – memory can extend beyond the confines of the body to involve coupled interaction with structures in the environment. At least some of our cognitive processes, in short, loop out into our surroundings.
Slime mould is an intriguing candidate to explore this idea because it doesn’t have a brain at all, yet in some cases can apparently ‘remember’ things without needing to store those associated memories within itself. In other cases, memories acquired via learning by one individual can even be acquired by a separate individual through physical contact. The behaviour of this strange form of life suggests that some of our ideas about how memories are acquired may need a rethink.
[...] Wherever they migrate, Physarum plasmodia leave behind extracellular slime trails – a non-living mucopolysaccharide. ... In principle, encountering the stuff could therefore tell the slime mould something about the availability of food in the area – but is extracellular slime used as a memory trace?
[...] Just as humans can use mobile phones or notebooks for memory storage and recall, slime moulds can use slime. Granted, numerical memory and navigational memory differ in kind, but the deeper point remains: Physarum evolutionarily stumbled upon an external solution for memory long before humans did.
The fact that extracellular slime can be used as a memory trace by any slime mould that is closely related to the one that left it also raises an important question: whose memory is it? [...] if slime qualifies as a memory trace, that memory belongs to the slime mould that encounters and uses it. The neurophilosopher Julian Kiverstein and I have dubbed this process – where memory storage and recall are tightly interlinked in cases of externalised spatial memory – ‘memory making’. In contrast, a memory trace that is acquired by learning and then stored inside an organism is not dependent upon that organism using it to qualify as (its) memory.
What makes slime mould memory so interesting is that – at least in some cases – it does not seem to require learning via direct experience, something that we might assume is necessary when we consider our own memories.
Since slime trails are left everywhere that a slime mould crawls, such potential memory is not the result of prior learning by the slime mould that left the cue. If this is correct, then Physarum’s use of extracellular slime provides an important example of memory without learning – where the external memory trace was not formed through learning on the part of the individual that left it...
[....] later research showed that slime moulds can even transfer memories from one individual to another. ... This raises a question: to whom does this memory belong? As with memory making, I would like to suggest that, in the case of transferred memory, it belongs to the plasmodial cell that uses the trace, given that its behaviour is guided by the trace. We can now justify taking this position for both types of memory without learning. If memory is a biological trait that is subject to natural selection, then selection primarily acts on the organism that derives a fitness advantage from using the memory trace.
[...] So, what can slime mould teach us about biological memory? One lesson is that spatial memory needn’t be confined entirely within an organism (á la HEC). Moreover, what becomes memory traces when used (eg, extracellular slime) needn’t be the result of learning by the external trace-producer.
Another takeaway is that, in some cases, an individual can acquire such memory without having engaged in learning itself. This raises an intriguing parallel in the human case. We do, after all, routinely read and act upon instructions, maps and manuals written by others, drawing on information acquired through their experiences, not our own.
Although such externalised sources of information are typically declarative in structure – designed to represent facts explicitly – we often act upon them automatically, without needing to consciously recall or reflect on the information they convey. In this way, they guide behaviour in ways that functionally resemble non-declarative memory.
While the analogy shouldn’t be pushed too far, both the human and slime mould cases illustrate how memory can become decoupled from individual learning, instead becoming accessible to others through environmental structures... (MORE - missing details)
EXCERPTS: . . . The differences between P polycephalum and humans may seem vast, but slime mould can reveal a remarkable amount about various aspects of how we remember. While many people might assume that our memories are primarily stored within our brains, some philosophers like myself argue that – along with some other aspects of cognition – memory can extend beyond the confines of the body to involve coupled interaction with structures in the environment. At least some of our cognitive processes, in short, loop out into our surroundings.
Slime mould is an intriguing candidate to explore this idea because it doesn’t have a brain at all, yet in some cases can apparently ‘remember’ things without needing to store those associated memories within itself. In other cases, memories acquired via learning by one individual can even be acquired by a separate individual through physical contact. The behaviour of this strange form of life suggests that some of our ideas about how memories are acquired may need a rethink.
[...] Wherever they migrate, Physarum plasmodia leave behind extracellular slime trails – a non-living mucopolysaccharide. ... In principle, encountering the stuff could therefore tell the slime mould something about the availability of food in the area – but is extracellular slime used as a memory trace?
[...] Just as humans can use mobile phones or notebooks for memory storage and recall, slime moulds can use slime. Granted, numerical memory and navigational memory differ in kind, but the deeper point remains: Physarum evolutionarily stumbled upon an external solution for memory long before humans did.
The fact that extracellular slime can be used as a memory trace by any slime mould that is closely related to the one that left it also raises an important question: whose memory is it? [...] if slime qualifies as a memory trace, that memory belongs to the slime mould that encounters and uses it. The neurophilosopher Julian Kiverstein and I have dubbed this process – where memory storage and recall are tightly interlinked in cases of externalised spatial memory – ‘memory making’. In contrast, a memory trace that is acquired by learning and then stored inside an organism is not dependent upon that organism using it to qualify as (its) memory.
What makes slime mould memory so interesting is that – at least in some cases – it does not seem to require learning via direct experience, something that we might assume is necessary when we consider our own memories.
Since slime trails are left everywhere that a slime mould crawls, such potential memory is not the result of prior learning by the slime mould that left the cue. If this is correct, then Physarum’s use of extracellular slime provides an important example of memory without learning – where the external memory trace was not formed through learning on the part of the individual that left it...
[....] later research showed that slime moulds can even transfer memories from one individual to another. ... This raises a question: to whom does this memory belong? As with memory making, I would like to suggest that, in the case of transferred memory, it belongs to the plasmodial cell that uses the trace, given that its behaviour is guided by the trace. We can now justify taking this position for both types of memory without learning. If memory is a biological trait that is subject to natural selection, then selection primarily acts on the organism that derives a fitness advantage from using the memory trace.
[...] So, what can slime mould teach us about biological memory? One lesson is that spatial memory needn’t be confined entirely within an organism (á la HEC). Moreover, what becomes memory traces when used (eg, extracellular slime) needn’t be the result of learning by the external trace-producer.
Another takeaway is that, in some cases, an individual can acquire such memory without having engaged in learning itself. This raises an intriguing parallel in the human case. We do, after all, routinely read and act upon instructions, maps and manuals written by others, drawing on information acquired through their experiences, not our own.
Although such externalised sources of information are typically declarative in structure – designed to represent facts explicitly – we often act upon them automatically, without needing to consciously recall or reflect on the information they convey. In this way, they guide behaviour in ways that functionally resemble non-declarative memory.
While the analogy shouldn’t be pushed too far, both the human and slime mould cases illustrate how memory can become decoupled from individual learning, instead becoming accessible to others through environmental structures... (MORE - missing details)