They don’t have a brain or nervous system. Where do they store memories? Mid-twentieth century research showing that one-celled life forms can learn was dismissed at the time for lack of a model.
But now researchers are taking a second look. Computer systems may offer a model for learning without a brain:
Key to the conundrum of how creatures with no brain or nervous system can learn is the assumption that memories are stored physically. Perhaps not. Michael Levin of Tufts University suggests an alternative approach that adapts concepts from artificial intelligence:
His group at Tufts University has been studying gene regulatory networks, which control gene expression, in individual cells. In a computational study published earlier this year, Levin and colleagues explored how these networks could shift their responses to certain stimuli or inputs without requiring underlying physical changes—much like how a computer doesn’t need to physically change its hardware when it records a piece of information typed into word processor.
In the simplest version of such a network, genes are assumed to be activated or inactivated by interactions with other genes or by stimuli from the external environment. Memory arises because the current state of genes in the network is dependent on all the interactions and inputs that occurred until now. In some situations the team has studied, this means that the network can be trained to learn certain associations and adapt its future behavior “not because we’ve changed the connections between genes A and B. . . . It’s simply that certain experiences change the overall stable state of the system in a way that changes how it reacts to those stimuli in the future.” Levin says.
CATHERINE OFFORD, “CAN SINGLE CELLS LEARN?” AT THE SCIENTIST (MAY 1, 2021) THE PAPER IS OPEN ACCESS.
In short, changes in the state of the life form, resulting in changed behavior — which amounts to learning — need not “be someplace” or weigh something, for the same reasons as a full USB stick doesn’t weigh any more than an empty one.
You may also wish to read: Why do many scientists see cells as intelligent? Bacteria appear to show intelligent behavior. But what about individual cells in our bodies?
and
What neuroscientists now know about how memories are born and die. Where, exactly are our memories? Are modern media destroying them? Could we erase them if we wanted to?