Rats know when they’ve forgotten something. Rats are aware of what they remember, and behave differently when they can’t remember.
Researcher Victoria Templer and her
research team at Providence College, in Rhode
Island in America, trained rats to dig through sand to sniff four samples: (1)
cinnamon, (2) thyme, (3) paprika or (4) coffee. The rats then had go to a dish
smelling of the matching scent. If the rats picked the correct dish, they got a
piece of cereal (New Scientist, 14 July 2017).
Rats that chose a
dish with the wrong scent received no reward. Rats that went to a fifth,
unscented dish received a quarter-piece of the cereal. This meant that when
rats forgot what they had smelled in the sand, their best choice was to pick
the unscented dish – but only if they knew that they had forgotten the relevant
smell.
Nine rats were each
tested many times across multiple experiments. In some of these, the unscented
dish was not there, forcing the rats to choose a scent even if they couldn’t
remember it. Without the unscented option, the rats picked the correct dish 52%
of the time.
When the fifth,
unscented dish was available, the rats chose the unscented option 20% of the
time. In those cases where they chose a scented dish, the rate of picking the right
dish increased to 61% of the time – an increase that wouldn’t be expected by
chance alone.
Because the rats’
performance improved when the unscented dish was available as an opt-out,
Templer says this shows that the rats weren’t simply choosing the unscented
dish for no reason. They seem to have known that declaring that they had
forgotten the smell would still earn them a small reward.
In further
experiments, the research team found that letting the rats sniff the sample
twice before choosing a match reduced how often they chose the unscented dish.
But making the rats wait longer between sniffing the sample and choosing a
match pushed up the number of times they opted out.
People and some
primates (apes) have “metamemory” – the ability to know what they remember.
However, whether rats have it too had been unclear, and this latest study
suggests that they might.
People with
Alzheimer’s disease or dementia often don’t realise when they have forgotten
something, so a test for metamemory in rats could be useful for rodent studies
of these conditions.
MARTINA NICOLLS is an international
aid and development consultant, and the author of:- Similar But Different
in the Animal Kingdom (2017), The Shortness of Life: A Mongolian Lament
(2015), Liberia’s Deadest Ends (2012), Bardot’s Comet (2011), Kashmir on a
Knife-Edge (2010) and The Sudan Curse (2009).
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