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If you learned to ride a bike as a kid, at some point you probably left the bike in the
garage for months or years before coming back to it.
And though you might have been a little wobbly when you finally decided to climb back on,
you never had to go through that training wheel phase that you did at the start.
The feeling is so familiar, it’s become a figure of speech.
When something's easy to remember after a long time not doing it, you say it's "like
riding a bike."
But this kind of memory really does stand apart from other kinds.
Even when people suffer memory loss, memories of how to do things often survive.
So why is riding a bike, just like riding a bike?
Motor memories get stored differently than lots of other memories, making them harder
to lose — but like other memories, there’s still a lot we don’t know.
Motor memory is the ability to repeat motions and remember motor skills.
It’s part of a category of memories called implicit memories, which are generally things
you learn less by thinking and more by doing.
And when you learn things without putting in specific effort to learn them, weird things
can happen.
Like, back in the 80s, 48 students were asked to identify what was in some incomplete photos.
Some they had just seen the full version of, but others were completely new to them.
But then, 17 years later, researchers got in touch with 12 of them, brought them back,
and compared them to a control group who had never seen any of the pictures before.
Those 12 still did better at identifying partial photos when they hadn’t seen the full version
in 17 years.
While the control group didn't show any difference.
4 of those12 also said they had no memory of even being in the study, which is part
of what makes it implicit.
No one ever sat them down to make them study up on photos because they were going to be
tested later, like you might for a test in school.
Those implicit memories also use different brain systems than other kinds.
One of the first on any list of brain parts related to memory is probably the hippocampus,
which is involved in making new memories.
But it’s less important for implicit and motor memories.
One reason we know this is from studying patients with amnesia.
When people suffer injuries to the hippocampus and nearby parts of the temporal lobe, they
tend to lose memories from before the injury, and also can't make new memories afterward.
These are called retrograde and anterograde amnesia, respectively.
And while it would be, of course, massively unethical to cause brain damage in order to
study memory, case studies of people who have suffered brain injuries can give us unique
insight.
Basically, if someone damages part of their brain and loses a certain function, you know
that part was necessary for that function.
And some of these cases have interesting twists.
For example, one patient spent years volunteering to shelve books at his library after a motorcycle
accident caused him to lose his hippocampus, preventing him from making new memories.
But he still learned the Dewey Decimal System — even though he couldn't tell you how he
learned it.
Which means that researchers have to look beyond the hippocampus to understand how implicit
memories work.
And for motor memories in particular, we've got a few leads.
One of these regions is the cerebellum.
That's a part of your brain that's separate from the cerebral cortex.
Other brain regions involved in memory, like the hippocampus, are part of the cerebral
cortex, so the fact that it's separate might be part of why this learning can be unconscious.
And one of its major purposes seems to be fine-tuning of motion.
That includes careful movements like balancing on a bike or playing the piano.
It's a complicated system, but some of the tools that make it all work are called Purkinje
cells.
They collect signals from neurons coming from other sensory systems, like sight and sound,
and convert them into a signal that fires at a variable frequency, up to 500 spikes
per second.
That signal gets sent to different motor systems, like hand grasping or gait, hopefully adding
up to a smooth, fluid motion.
One of the mysteries, though, is that this might not be where these memories are stored.
Instead, research has pointed to changes in a number of different brain regions — not
all of which are where we’d expect.
For example, in a study published in Nature in 2004, 24 people were split into two groups,
one of which was asked to learn to juggle.
After about 3 months of practice, they could juggle for a solid 60 seconds.
The researchers scanned their brains and found changes in the temporal lobe and the intraparietal
sulcus in the group who learned to juggle.
These weren’t regions associated with memory per se — instead they had to do with tracking
visual motion and planning hand movements.
But then, 3 months after that, the volunteers got their brains scanned again, and those
changes were still there, though they were a little smaller.
That’s even though none of them reported continuing to practice.
I guess once scientists tell you are done, you just stop juggling.
Come on!
Have some fun!
But similar studies found other brain locations were important — so we probably won’t
ever tie motor memories to just a single location or process.
And those neurons in the cerebellum might not be just for motor skills.
There’s evidence some cognitive tasks require them as well.
Some research has even tied them to emotional experiences.
So the next time you get back on your bicycle, give some thanks at least in part to your
cerebellum!
It’s one of the major things keeping you balanced and upright — and contributing
to your ability to hold on to that for years.
Thanks for watching this episode of SciShow Psych.
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