Tuesday, March 10, 1998
Psychologists reveal memory’s complexity
RESEARCH: Discovery may lead to better treatment for amnesia,
Parkinson’s disease patients
By Matt Grace
Daily Bruin Contributor
For anyone who has walked to the refrigerator, opened the door,
stared inside and then wondered why you are there, when just
moments before you got up to do something completely different,
relax. You are not alone.
A recent study on learning mechanisms – like the habit-formed
behavior above – by UCLA psychologist Barbara Knowlton provides new
insight into the regions of the brain responsible for learning and
memory.
"It seems that memory is composed of multiple systems," Knowlton
said. "There are different kinds of memory that depend on different
brain systems."
Knowlton tested amnesiacs with a dysfunctional hippocampus and
patients with Parkinson’s disease – a disorder affecting the basal
ganglia.
When either of these brain systems fail, individuals reflect a
corresponding difficulty learning new things depending on the
region affected.
"This particular project is to see if we can understand more
about the role of these structures," Knowlton said. "Potentially
that could help design therapeutic treatments and help to
understand these (disorders) a little more.
"The hippocampus is more important for conscious explicit
learning of facts and events," Knowlton said, and the basal ganglia
is fundamental for "implicit or unconscious learning."
Explicit memory refers to the processes through which people
deliberately attempt to learn and recollect something – like
studying for a test.
In contrast, implicit memory operates on a unconscious level.
Skills like riding a bike involve the automatic recollection and
influence of prior experiences.
The research focused on habit-learning – a form of implicit
memory which relies on the gradual acquisition of associations or
cues.
For example, learning the route to a specific destination like
school depends on habit-learning. At first, a person must think
about the street names and the appropriate turns Eventually, the
route becomes automatic; recognition of certain visual cues
decreases the amount of original thought needed until a habit
forms.
"In a well-learned habit you are just responding based on the
stimuli," Knowlton said, "not on whatever goal that stimulus was
ultimately paired with."
Knowlton provided evidence for this in an experiment using rats.
After the rats learned to associate a light in a maze with food,
Knowlton laced the food with a drug that made the rats sick; as a
result the rats no longer were interested in the food.
Knowlton found that the rats go to the light regardless of the
food, poisoned or not, because they have learned a habit via the
basal ganglia.
Experiments involving humans with dysfunctional areas of the
brain offered additional evidence.
People with damage to the hippocampus have trouble consciously
learning new things. However, improving motor skills like their
tennis stroke or golf swing is not a problem.
Likewise, these individuals perform well on a task which tests
for the ability to develop unconscious habits.
"It’s clear that these patients can learn some kinds of new
things, and, thus other parts of the brain that are not damaged
must have some kind of memory function," Knowlton said.
In addition, Knowlton studied the abilities of patients with
Parkinson’s disease to perform simple memory and learning
tasks.
These individuals, who normally have trouble with motor skills –
muscle rigidity, slowness, and tremors – possess perfectly
functional explicit or conscious memories.
"When given a memory test for words or pictures, they would do
fine, unlike the amnesiacs who normally do poor on such tests,"
Knowlton said.
However, these same Parkinson’s disease individuals perform very
poorly on a test measuring their ability to develop unconscious
habits, Knowlton said. They may remember the test, but they are
never able to pick-up any habits.
As a result, Knowlton concluded the basal ganglia is an
important structure for this kind of implicit learning. The basal
ganglia appear to have memory functions that other brain structures
are unable to take over, Knowlton said.
Researchers have been trying to use the intact habit system to
help amnesiacs with a dysfunctional hippocampus to learn new
things, but Knowlton said the process is difficult.
"I think it’s hard, since as humans, we’re so tied into our
conscious memory and it’s hard to kind of trust your gut feeling
and instincts."
In terms of Parkinson’s patients, Knowlton said the
characterization of the different memory systems has helped
psychologists understand that these people might have some problems
that have previously gone unnoticed.
"Hopefully by elucidating the nature of this impaired learning,
we may be able to suggest rehabilitation and assessment ideas,
besides knowing more about what type of learning the basal ganglia
mediate," said Jennie Sage, a third-year behavioral neuroscience
graduate student, who worked on the project with Knowlton.
"Identifying brain systems responsible for memory could help us
identify the molecular events that underlie memory storage, which
could have implications for the development of treatments for
diseases that effect memory like Alzheimer’s," Knowlton said.
"Also, identifying the properties of different memory systems
could lead to rehabilitation treatments that exploit other systems
to make up for the lost system."