BUMBLEBEES MAKE FALSE MEMORIES , TOO
It's well known that
our human memory can fail us. People can be forgetful, and they can sometimes
also "remember" things incorrectly, with devastating consequences in
the classroom, courtroom, and other areas of life. Now, researchers show for
the first time in the Cell Press journal Current Biology on February 26 that bumblebees can be
unreliable witnesses too.
The new study is the
first to explore false memories in any non-human animals, the researchers say.
They now suspect that the phenomenon may be widespread in the animal kingdom.
"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," says
Lars Chittka of Queen Mary University of London. 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."
Bumblebees are rather
clever animals, which explains why Chittka has been studying learning and
memory in the insects for the last 20 years. The bees can remember the
patterns, colors, and scents of various kinds of flowers. They can also
navigate to those flowers and back home again over long distances.
Most times when people
have studied memory in animals, errors in performance have been taken to mean
that the animals failed to learn the task or perhaps learned it and then
forgot. But Chittka and his colleague Kathryn Hunt wondered: What if animals
can experience a more interesting type of memory failure?
To find out, Chittka
and Hunt first 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, bees 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, the bees 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 bees 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.
Chittka and Hunt say
that the insects' observed merging of long-term memories is similar to the
memory conjunction errors humans sometimes make. They 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. In fact, Chittka's team recently found that people who are
particularly good at learning rules to classify objects are also especially
prone to these false memory illusions.
"There is no
question that the ability to extract patterns and commonalities between
different events in our environment [is] adaptive," Chittka says.
"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 bees, 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. Chittka's lab is now using radar tracking to follow
bees and their choices of flowers over a lifetime.
"We are
fascinated to learn how lifetime experiences accumulate and are integrated in
making day-to-day foraging decisions," he says.
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