Can single-cell organisms learn?

By | May 6, 2021

Catherine Offord writes:

Even by her own telling, Beatrice Gelber’s work was offbeat. It was October 1960, and Gelber had recently opened a facility called the Basic Health Research Institute in Tucson, Arizona. Described as an “enthusiastic psychologist” by the newspaper interviewing her about her work, Gelber explained how, several years earlier, she’d discovered an unexpected behavior in a protozoan called Paramecium aurelia. This unicellular organism, she claimed, had shown it was capable of learning, a feat generally assumed to be restricted to what were considered higher organisms such as mammals and birds. Fellow scientists “all thought I was plain crazy when I started,” she told the Tucson Daily Citizen. “But now they think I may have something.”

Gelber had gotten into science relatively late in life, after the youngest of her three children had flown the nest. While a PhD student at Indiana University in Bloomington, she had become interested in Paramecium’s apparently complex behavior, and started trying to train the ciliated cells to associate a stimulus with a reward, much as the famous 19th-century physiologist Ivan Pavlov had conditioned dogs to associate the sound of a buzzer with the presentation of a tasty snack. Housing each culture of Paramecium in a little pool on a microscope slide, she inserted a piece of wire coated in bacteria—food, from the protozoan’s perspective—and watched as her subjects, although initially timid, soon swam over. After several trials, she found that she could put just the wire, clean of any bacteria, into the liquid, and elicit the same food-seeking behavior.

To Gelber, the experiments demonstrated that Paramecium was learning to associate the wire with food, a conclusion that challenged scientists’ belief that only highly evolved, multicellular animals with central nervous systems were capable of such behavior. More fundamentally, her results suggested that at least some of the biological machinery needed for learning and other cognitive processes might exist not in the connections among neurons in an animal brain, but within individual cells themselves. “Possibly the biochemical and cellular physiological processes which encode new responses are continuous through the phyla,” Gelber speculated in one 1962 paper, “and therefore would be reasonably similar for a protozoan and a mammal.”

Her conclusions touched a nerve in the wider scientific community. While some colleagues viewed her ideas with interest, her many critics argued that her experiments omitted vital controls needed to rule out other, simpler explanations for her results, such as tropism—an essentially automatic response or movement of an organism relative to a stimulus, such as a wire or food. More egregiously, some claimed, she seemed to be ignoring a well-accepted division between us and them: “Gelber freely applies to Protozoa concepts (reinforcement and approach response) and situations (food presentation) developed with higher metazoan animals,” wrote Paramecium researcher Donald Jensen in 1957. “I feel that such application overestimates the sensory and motor capabilities of this organism.”

Gelber’s work had all but disappeared from view by the time she died in 1991; a search for her name in academic papers between 1980 and 2020 suggests that she was barely mentioned during that time. But now, seven decades after she started her experiments, a group of researchers at Harvard University are arguing that her ideas deserve a revival. [Continue reading…]

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