When recalling memories, some individuals can remember items incorrectly. Tiny, buzzing little insects known as bumblebees can be unreliable witnesses too, according to a new study published in the journal Current Biology – the first to explore false memories in any non-human animals.
The early bumblebee (Bombus pratorum), one of the smaller bumblebees. Image credit: Bernie Kohl.
“We discovered that the memory traces for two stimuli can merge, such that features acquired in distinct bouts of training are combined in the animal’s mind. As a result, stimuli that have actually never been viewed before, but are a combination of the features presented in training, are chosen during memory recall,” said Dr Lars Chittka of Queen Mary University of London, who is a co-author on the study.
Dr Chittka and his colleague, Dr Kathryn Hunt, trained bumblebees to expect a reward when visiting a solid yellow artificial flower followed by one with black-and-white rings or vice versa.
During subsequent tests, bumblebees were given a choice between three types of flowers. Two were the yellow and the black-and-white types they’d seen before. The third type of flower had yellow-and-white rings, representing a mixed-up version of the other two. Minutes after the training, they showed a clear preference for the flower that most recently rewarded them. Their short-term memory for the flowers was good.
One or three days later, however, something very different happened when the bumblebees’ memory was put to the test.
At first, the bumblebees showed the same preference displayed in the earlier tests, but as the day wore on, they appeared to grow confused.
Half of the time, they began selecting the flower with yellow rings, even though they’d never actually seen that one in training before.
“The insects’ observed merging of long-term memories is similar to the memory conjunction errors humans sometimes make,” the scientists said.
“We don’t think those false memories in either bumblebees or humans are simply bugs in the system, but rather are side effects of an adaptive memory system that is working rather well.”
Dr Chittka added: “there is no question that the ability to extract patterns and commonalities between different events in our environment is adaptive.”
“Indeed, the ability to memorize the overarching principles of a number of different events might help us respond in new situations. But these abilities might come at the expense of remembering every detail correctly.”
In bumblebees, with their limited brain capacity, the pressure to economize by storing overarching features of a class of objects rather than each individual object might be even more intense.
“We are fascinated to learn how lifetime experiences accumulate and are integrated in making day-to-day foraging decisions,” Dr Chittka said.
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Kathryn L. Hunt & Lars Chittka. Merging of Long-Term Memories in an Insect. Current Biology, published online February 26, 2015; doi: 10.1016/j.cub.2015.01.023
