Researchers from the University
of Toronto, Canada, have discovered a reason why we often struggle to remember
the smaller details of past experiences. They found that there are specific
groups of neurons in the medial prefrontal cortex (mPFC) of a rat’s brain – the
region most associated with long-term memory. These neurons develop codes to
help store relevant, general information from multiple experiences while, over
time, losing the more irrelevant, minor details unique to each experience. The
findings provide new insight into how the brain collects and stores useful
knowledge about the world that can be adapted and applied to new experiences. Memories
of recent experiences are rich in incidental detail but, with time, the brain
is thought to extract important information that is common across various past experiences.
They predicted that groups of neurons in the mPFC build representations of this
information over the period when long-term memory consolidation is known to
take place, and that this information has a larger representation in the brain
than the smaller details.
To test their prediction, the
team studied how two different memories with overlapping associative features
are coded by neuron groups in the mPFC of rat brains, and how these codes
change over time. Rats were given two experiences with an interval between
each: one involving a light and tone stimulus, and the other involving a
physical stimulus. This gave them two memories that shared a common stimulus
relationship. The scientists then tracked the neuron activity in the animals’
brains from the first day of learning to four weeks following their
experiences. This experiment revealed that groups of neurons in the mPFC
initially encode both the unique and shared features of the stimuli in a
similar way. Further experiments also revealed that the brain can adapt the
general knowledge gained from multiple experiences immediately to a new
situation. Concluding, researchers showed that groups of neurons develop coding
to store shared information from different experiences while, seemingly
independently, losing selectivity for irrelevant details.
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