Single Cell Could Be Capable Of 'Learning': Study

Cells, such as those making up human bodies, might be capable of 'learning', once deemed exclusive to complex creatures with brains, including birds and mammals, a new study has suggested.

Habituation is a simple form of learning in which one's response to a certain trigger lessens with repeated exposure. It is how one learns to ignore things happening often, such as the ticking of a clock. Habituation can also help people confront their fears.

The study offered "compelling evidence" that even single-cell creatures such as amoebae, as well as the cells in human bodies, could show habituation similar to that seen in complex organisms with brains and nervous systems, said researchers, led by those at Harvard Medical School, US, and the Centre for Genomic Regulation, Spain.

The results, published in the journal Current Biology, added to a small but growing body of evidence in this field and deepen our understanding of how learning and memory work at the most basic level of life, they said.

"This finding opens up an exciting new mystery for us: How do cells without brains manage something so complex?" said senior author Jeremy Gunawardena, an associate professor of systems biology at Harvard Medical School.

Gunawardena's team had earlier documented evidence of a single-celled ciliate displaying avoidance behaviour, similar to that observed in animals when they encounter unpleasant situations. A ciliate uses hairs on its surface for moving and eating.

The findings suggested that a single cell is capable of behaviour more complex that what is currently appreciated, the researchers said.

For the study, the researchers used computer models to analyse how molecules inside ciliates and cells of mammals respond to different patterns of stimulation, or something that triggers a physical or behavioural change.

They found four networks of molecules that displayed hallmarks of habituation, usually seen in animal brains. Each of the molecule networks were found to have two forms of "memory" storage that captured information learned from the environment.

Further, one of the memory form was found to decay much faster than the other -- a form of memory loss necessary for habituation, the researchers noted.

If single cells can "remember", it could also help explain how cancer cells develop resistance to chemotherapy or how bacteria become resistant to antibiotics -- situations where cells seem to "learn" from their environment, they said.

However, these possibilities would need to be explored with real-world biological data, the team said.

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