It is not surprising that a good night’s sleep
improves our ability to remember what we learned
during the day. Now, researchers at the RIKEN Brain
Science Institute in Japan have discovered a brain
circuit that governs how certain memories are
consolidated in the brain during sleep. Published in
the May 26 issue of Science magazine, the study
shows how experimentally manipulating the identified
neural connection during non-REM sleep (deep sleep)
can prevent or enhance memory retention in mice.
The team led by Masanori Murayama studied the
long-known phenomenon of memory consolidation during
sleep: perceiving texture requires signaling within
a neural circuit from higher-level motor-related
brain regions back to lower-level touch-related
sensory areas.
They reasoned that the same “top-down” pathway might
also consolidate memories of textures.
Explains Murayama, “There is a long standing
hypothesis that top-down input is crucial for memory
consolidation and that during sleep, neurons in
sensory regions activated during the initial
experience can “reactivate” by unknown pathways. We
found such reactivation of the top-down pathway is
critical for mice to encode memories of their
tactile experiences.”
The researchers developed a task to assess memory
retention that relies on the natural inclination of
mice to spend more time investigating new items in
their environment.
First they allowed mice to explore objects in two
rooms with smooth floors, then they changed one of
the smooth floors to a textured floor and again
allowed the mice to explore.
With normal sleep, mice spent more time exploring
the room with the textured floor, showing that they
remembered the smooth room and were less interested
in it. Typically, this behavior was observed as long
as the second exploration occurred within two days.
To examine whether the top down circuit was
responsible for memory consolidation during sleep,
they manipulated the mice in several ways.
First, they showed that sleep deprivation
immediately following the first tactile experience
caused mice to explore the textured room less often
on the second exploration, indicating that they did
not remember the smooth room.
Next, they inactivated the top-down neural pathway
during non-REM sleep shortly after the first
exploration and found that during the second
exploration, mice performed as if they had been
sleep deprived.
Silencing the top-down pathway when mice were awake
or during non-REM sleep at later times had no effect
on performance, indicating that memory consolidation
happened in the first bout of non-REM sleep after
the experience.
The importance of top-down circuit activation in
non-REM sleep suggested that memory consolidation
might involve synchronous slow wave brain activity
between the two brain regions that is characteristic
of non-REM sleep.
To test this, they artificially applied synchronous
or asynchronous activity in the higher and lower
regions of the circuit during non-REM sleep after
the first tactile experience.
Mice with asynchronous activation were unable to
consolidate memories, but synchronous activation
allowed them to retain a strong memory of the smooth
floor for at least 4 days or twice as long as
normal.
The synchronous treatment even rescued the typical
lack of memory retention in sleep-deprived mice.
“Patients who suffer from sleep disorders often have
impaired memory functions. Our findings suggest a
route to therapy using transcortical magnetic or
direct-current stimulation to top down cortical
pathways to reactivate sleep-deprived neurons during
non-REM sleep.
Our next step is to test this in mouse models of
sleep-disorders" says Murayama.
For more information
Top-Down Cortical Input during NREM Sleep
Consolidates Perceptual Memory
Daisuke Miyamoto, Daichi Hirai, Chi Chung Alan Fung,
Ayumu Inutsuka, Maya Odagawa, Takayuki Suzuki, Roman
Boehringer, Chinnakkaruppan Adaikkan, Chie
Matsubara, Norio Matsuki, Tomoki Fukai, Thomas J
McHugh, Akihiro Yamanaka & Masanori Murayama
Science, doi: 10.1126/science.aaf0902
Link...
MDN |