Scientists Discover How We Play Memories in Fast Forward
Scientists at The University of Texas at Austin have discovered a
mechanism that may explain how the brain can recall nearly all of what
happened on a recent afternoon — or make a thorough plan for how to
spend an upcoming afternoon — in a fraction of the time it takes to live
out the experience. The breakthrough in understanding a previously
unknown function in the brain has implications for research into
schizophrenia, autism spectrum disorders, Alzheimer’s disease and other
disorders where real experiences and ones that exist only in the mind
can become distorted.
The newly discovered mechanism, which compresses information needed
for memory retrieval, imagination or planning and encodes it on a brain
wave frequency that’s separate from the one used for recording real-time
experiences, is described in a cover article in the Jan. 20 print
edition of the journal Neuron.
Brain
cells share different kinds of information with one another using a
variety of different brain waves, analogous to the way radio stations
broadcast on different frequencies. Laura Colgin,
an assistant professor of neuroscience, Chenguang Zheng, a postdoctoral
researcher, and their colleagues found that one of these frequencies
allows us to play back memories — or envision future activities — in
fast forward.
“The reason we’re excited about it is that we think
this mechanism can help explain how you can imagine a sequence of events
you’re about to do in a time-compressed manner,” says Colgin. “You can
plan out those events and think about the sequences of actions you’ll
do. And all of that happens on a faster time scale when you’re imagining
it than when you actually go and do those things.”
In the brain,
fast gamma rhythms encode memories about things that are happening right
now; these waves come rapidly one after another as the brain processes
high-resolution information in real time. The scientists learned that
slow gamma rhythms — used to retrieve memories of the past, as well as
imagine and plan for the future — store more information on their longer
waves, contributing to the fast-forward effect as the mind processes
many data points with each wave.
Mental compression turns out to
be similar to what happens in a computer when you compress a file. Just
like digital compression, when you replay a mental memory or imagine an
upcoming sequence of events, these thoughts will have less of the rich
detail found in the source material. The finding has implications for
medicine as well as for criminal justice and other areas where memory
reliability can be at issue.
Colgin notes that the research could
also explain why people with schizophrenia who are experiencing
disrupted gamma rhythms have a hard time distinguishing between imagined
and real experiences.
“Maybe they are transmitting their own
imagined thoughts on the wrong frequency, the one usually reserved for
things that are really happening,” says Colgin. “That could have
terrible consequences.”
Next, the researchers plan to use animals
with neurological disorders similar to autism spectrum disorders and
Alzheimer’s disease in humans to better understand what role this
mechanism plays and explore ways to counteract it.