Wild brown rats are naturally nocturnal
with sleeping patterns during the day and activity at night. These periods
of activity have been observed as falling into the three main time brackets of
dusk, just prior to dawn, and a period in between. Pet rats on the
other hand are quite happy to fit in with our more diurnal (asleep at night) lifestyle
and will easily adapt. Pet rats, as with their wild cousins,
purposely build 'nest like' beds if you provide bedding material and they
will happily sleep alone or bundled on top of each other in a heap. Here
is a video of my rat (Sally) accepting or procuring some bedding of her own accord.
When one of my pet rats gets
sleepy, it will tend to sit comfortably for a period of time before moving
into a sleeping position. Rats may turn around as they find a good spot as
well as stretch and yawn as fatigue sets in. Once rats fall asleep they
will dream as part of their differing sleep phases in the same manner as
humans. These dreams will be produced from both the memory and visual
areas of the brain so rats will remember things they do and see. When a
rat first falls asleep they are easily aroused but if the disturbance is
minimal and they are sleepy they will soon drop off again quickly.
A cold rat getting
ready to sleep will curl up into a ball and wrap its tail close to its
body to conserve heat. As they enter their deep sleep phase or begin to
feel warmer they may straighten up. A warm rat will happily go into the
'eel' position and stretch out its body with its tail straightened. It's
common to see rats stretched out when part of a heap and it's no wonder
since they are surrounded by 'hot water bottles'.
After entering their deep sleep phase
my most trusting rats will allow me to
pick them up without displaying the slightest anxiety, or even (it
appears) awareness.
Such rats can easily be cupped in both hands and raised from their bed
without any movement at all.
It's a truly wonderful experience that gives you a sense of total peace
and oneness with the little one.
This following video was taken on
the same day Sally and Rena arrived at their new home. Their journey from
the rat breeder was a daytime trip of
about 6 hours. They were excited and alert for the whole journey and it upset their sleeping
pattern so by the time they arrived they were very tired. The room temperature was
a comfortable 27.C and
as they didn't
curl into a ball they appeared to be quite cosy. I was fortunate to see them in that position
for a long period and as I watched I could see their limb and facial twitches very
clearly as they dreamed.
As of writing, my work
schedule is generally erratic but on some days there is a set pattern that
can last for a few weeks. During busy periods when I'm working late in the
rat's room I usually stay there to sleep. If I should wake up just before
the alarm clock rings on one of those set mornings I'm no longer surprised
to see one of my rats (Sally) perched knowingly just under the release
hatch. Sally appears to have synchronised her circadian rhythm to my own.
I don't know if it's every day or just on those set mornings (and I'm not
willing to find out).
During the day my home is empty so I
make sure the rats get a good few hours of free roaming time at night and
some limited time in the morning. My young rats are so incredibly
manic in the morning and evening so I expect the bulk of their sleep is during
the day with some additional sleep during the night.
On my rest days and shorter days the
rats can run around for as long as I'm home. Young rats are best described
as pocket dynamos that won't stop spinning. Trips back to
the cage are only for food, drink, and the toilet (hopefully). As they get
older, they have an initial manic period and then calm down to
intermittent manic/scamper pace. When they do decide to rest without coersion they know what's good for them and
will more often than not snuggle up inside your clothing (both being worn
or folded elsewhere) for a nap.
The following relate to rat dreams
and memory
I had an a-maze-ing dream last
night
In a 2001
study,
Matthew A. Wilson, professor of brain and cognitive sciences at
MIT's Picower Institute for Learning and Memory, and postdoctoral
associate
Daoyun Ji examined rat's brain activity as they dreamt about
mazes they had earlier run through. The study showed that rats formed
complex memories of events and that these memories were replayed while the
rats slept.
As humans dream,
they produce brain activity in both the hippocampus (memory centre) and
the visual cortex (images). Activity in the rat's hippocampus and visual
cortex was present and Wilson and Ji were able to demonstrate that
replayed memories did contain visual images from the maze running
experience.
"This work brings us closer to an
understanding of the nature of animal dreams and gives us important clues
as to the role of sleep in processing memories of our past experiences,"
Wilson said.
Wilson and Ji were recorded spiking
patterns of electrodes in individual neurons within a rat's brain and
compare the activity of the neurons when the rat was awake and asleep. The
comparison displayed that neurons activated when the animal experiences an
event while awake such as running through a maze are reactivated during
sleep. The hippocampus and the region of the cortex associated with
processing input from the senses 'communicate' with each other as the rat
sleeps which researchers suggest helps to reinforce and consolidate
memories.
Sleep, Memory
Here's an update on the sleep, dream, memory connection.
BOSTON, Mass. - March 30, 2007 - Scientists have known for
50 years that the brain handles short- and long-term memories in different
ways.
Now researchers in Boston are contributing to a growing understanding of
the role of sleep in transforming memory. WBUR's Health and Science
reporter Allan Coukell explains.
ALLAN COUKELL: We take it for granted that we know what memory is -- like
it's some sort of mental backpack that we can put stuff in and take out
when we need it again. But Matt Wilson says much about memory is still a
mystery.
MATT WILSON: We tend to think of memory simply as storage and retrieval. I
show you a face, tomorrow you recognize the face. I give you a phone
number, five minutes from now you are able to write down that phone number
again. But ultimately, I think memory is a component of broader system of
learning.
Wilson, a professor of neurobiology, keeps a symbol of memory -- a glass
statue of a sea horse -- on a table in his office at MIT.
The Latin for sea horse is "hippocampus." And hippocampus is the sea
horse-shaped part of the brain that Wilson studies. It is crucial for
making new memories.
CLICK OF LOCK, AS DOOR OPENS.
To see memory in action, Wilson and his post doc researcher Miguel
Remondes have been running rats through mazes.
MIGUEL REMONDES: In this maze, basically the rat has to go around the
circle and choose which entry to take...
The maze is shaped like a wagon wheel. If the rat enters the spokes in the
right order, he's rewarded with a sip of chocolate syrup.
REMONDES: He's drinking the reward right now...
As the rat runs, electrodes monitor the activity of cells in his
hippocampus.
REMONDES: He didn't go through number one, he went through number two.
COUKELL: Clever rat!
REMONDES: Yeah, he is clever (laughs).
Converted to sound, you can hear the crackling of about a hundred brain
cells. There's a distinct pattern that corresponds to the rat's physical
movements -- each twist and turn of the maze. Matt Wilson has found that
when the rat sleeps his brain plays back the same pattern of activity.
WILSON: They are replaying in an almost literal sense. You might think of
replaying a movie that you just watched.
And it's not just the hippocampus. The "higher" visual cortex of the brain
is also replaying its activity. It's as if the sleeping rat is re-living
his experience. Wilson believes this coordinated replay may be a sign of
memory being transformed, or consolidated, in the brain.
And evidence from human studies shows a similar effect.
MATT WALKER: The way we go about testing these questions is we'll usually
train subjects on memory tasks.
Matt Walker is a sleep and memory researcher at Beth Israel Deaconess
Medical Center.
WALKER: So subjects would sit at a computer keyboard and using their left
hand they would type out a particular sequence, such as 4-1-3-2-4.
Walker's subjects practice the task over and over. Then, after a 12-hour
break, they're re-tested for speed and accuracy. The performance of
subjects who stay awake doesn't change. But those who sleep during their
break improve by twenty to thirty percent.
WALKER: So in other words, following practice, your brain will continue to
learn in the absence of any further training. So it is really quite
magical. However, that delayed learning occurs exclusively across periods
of sleep.
Walker has also shown that depriving someone of sleep for one full night
and then giving them catch-up sleep on later nights produces no
improvement. As Walker puts it, "if you don't snooze, you lose."
Some scientists remain skeptical of the link between sleep and memory.
Jerry Siegel, a sleep researcher at UCLA, points out that many people do
not experience REM, or "dreaming", sleep at all.
JERRY SIEGEL: People who don't have REM sleep either through brain injury
or taking drugs have no cognitive deficit whatsoever. And there are people
who have gone without REM sleep for years.
Matt Walker, of Beth Israel Deaconess, counters that the different phases
of sleep seem to serve different functions. He says REM sleep appears most
important for reinforcing emotionally charged memories -- precisely the
area where brain injury patients and people on psychotropic drugs often
have trouble.
But if memory isn't a backpack where facts and experiences are preserved,
what is it? And what is the role of sleep? Matt Wilson of MIT believes we
process memories so we can re-evaluate them:
WILSON: Either for the purpose of selecting and strengthening certain
memories. Or I think more importantly for going back and comparing
different experiences that may have occurred at different times. And the
reason for comparing is so that one can learn from them.
A decade ago, there was little scientific evidence to explain why we
sleep. The emerging science of memory provides at least some explanation
of what's going on during that third of our lives. For WBUR, I'm Allan
Coukell.
Sidebar: Meat versus Machine
Matthew Wilson believes that the brain processes memory to develop
"wisdom"--which he defines as the ability to make the right decision based
on partial information. That is also one goal of research in artificial
intelligence, and Professor Wilson (who trained as an engineer) finds an
interesting correlation between how rats replay their experiences and how
some computers make decisions.
It seems that when the rats are asleep, they normally play their
experiences forward. But when they are just resting -- daydreaming, Wilson
calls it -- the replay patterns run backwards.
Rich Sutton, an artificial intelligence researcher at the University of
Alberta, says a number of computer algorithms, so-called reinforcement
learning algorithms, also work backwards. "These are algorithms designed
for whenever you have a sequence of decisions to make. It's been applied
to autopilots for helicopters, computer games; many, many robots,
financial applications, logistics."
Professor Sutton, who studied psychology before switching to computers,
says maybe it isn't surprising that a rat learning to remember a maze
would start with the reward and work backward to figure out how he got it.
The same principals of efficient processing could apply to animals and
computers.
