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Saturday, December 19, 2009

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 A Brain Drain
Joseph Brean,  National Post  

 
In hospital etiquette, Alzheimer's patients pose a problem for the busy
clinician passing them in the hallway. Is it rude not to say hello to
someone who does not remember ever having met you?

Marcia Sokolowski, clinical ethicist at Baycrest Centre for Geriatric Care
and the University of Toronto Joint Centre for Bioethics, once asked a
patient her thoughts on this.

"I won't remember you, but say hi," the woman said. "I'll have a feeling
about you."

Maybe she was just being polite, but her answer goes deeper than manners. It
illustrates the multiplicity of memory. It hints at what science has slowly
realized, that recognizing someone's face is not the same as remembering
their name, or that you know them, or remembering a particular time you
spent together. While each of these faculties may be damaged to the point of
failure, others can more or less survive and create the patient's vague
"feeling" of familiarity.

Like pauses in Harold Pinter's plays, or silence in John Cage's music, the
many kinds of forgetfulness stand in illuminating contrast to human memory.
They show that remembering, like forgetting, is not always an all-or-nothing
deal. It comes in parts, known as modules, such as memory for faces, skills,
facts, or episodes in one's life.

Some of the more mysterious cognitive pathologies illustrate this aspect of
memory, such as Capgras Syndrome, in which a person recognizes their loved
ones' faces but feels no emotional familiarity, and so believes they have
been replaced with impostors; or prosopagnosia, better known as
"face-blindness," in which people cannot recognize faces, but can sometimes
"figure them out" based on other cues, such as hair or clothing or body
shape.

But the clearest evidence for the diversity of memory has come from the
physical brain itself, and from seeing what happens when the key brain
structures involved in memory are diseased, injured, or surgically removed.
These include the "stupid," sea horse-shaped hippocampus and the
"emotional," almond-shaped amygdala, both deep in the middle of the head,
behind the nostrils at the top of the spinal cord; and "the boss," the
neocortex, behind the forehead.

Scientists have learned what kind of chemical changes must take place within
and among brain cells in order to create, retain, recall and strengthen
memories. They know where to look for the activity of memory in a healthy
brain, and have a good idea of how and why specific forms of amnesia arise
from specific kinds of brain damage.

"In that sense, we know what's going on," said Morris Moscovitch, a
University of Toronto psychologist. "But the exact location where a memory
is, I think, is something that we don't know and probably never will know."

He means that there is no such singular place, that memories are distributed
in parts throughout the brain, and remembering is the process of gathering
these parts together. This premise underlies his "multiple trace theory," a
leading account of memory.

It begins with the observation that semantic memories, for general facts
about the world, seem to last longer than episodic memories, for events in
one's life. After showing this to be clearly true among Alzheimer's
patients, Dr. Moscovitch and his colleague Lynn Nadel "found this
disconcerting," he said.

One possible explanation was that facts (Paris is the capital of France) are
called to mind more frequently than scenes (seeing the Mona Lisa for the
first time), and so they are rehearsed and reinforced to a greater degree.
Another is that plain facts are not terribly rich, content-wise, and are
just more simply stored.

A few years ago, Dr. Moscovitch met the world's most famous amnesic, Henry
Molaison, in a U.S. nursing home. He found him to be "a very simple person,
a plain person."

In 1953, Mr. Molaison, known to the world as H.M. until his recent death,
lost the ability to form new memories when two large chunks of his brain,
including almost all his hippocampus, were surgically removed to cure his
recurring seizures. But while he could no longer lay down new memories of
his experiences, he did not seem to have lost his old ones. The hippocampus,
therefore, seemed crucial to creating episodic memories, but they seemed to
be stored elsewhere.

Also, his pre-existing semantic memories were largely preserved, and he
remained generally intelligent, aware, and able to learn new skills. So
memory for facts and skills also seemed to be happening outside the
hippocampus.

The hippocampus is "stupid," Dr. Moscovitch says, because its role is to pay
attention to anything that passes through consciousness, regardless of its
relevance, truth, or possible usefulness. It does not care if you are
experiencing something, dreaming it or imagining it. It cannot predict what
you will need to remember in future, and so its job is to make a record of
everything, no matter what, but not to organize it.

It creates a linkage between itself and the neocortex, much like a reference
card links to a book in a library. This link between two brain structures,
this "ensemble of neurons," is the "trace" of "multiple trace theory." The
neocortex is a smarter brain region. It deals with complex and abstract
thought, and gives order to the information flowing through the hippocampus.
In evolution, it is the most recent of the brain's structures, and because
of its role in giving an organizational structure to memory, Dr. Moscovitch
calls it "the cross-examiner," or "the boss."

People with damage to this part of the brain often confabulate, or invent
stories in a process psychologists call "honest lying."

"They will confabulate, tell stories about their past that are
self-contradictory and patently false. Sometimes they're so bizarre that you
don't need to know very much about the individual to know that the memory is
impossible. But often it seems possible until you find the person
contradicting himself," Dr. Moscovitch said.

In a recent paper, Dr. Moscovitch describes memory traces as "beads in a
jar," meaning they are stored randomly, and independently of each other. In
remembering, the neocortex gathers them together, compares their semantic
content to see if it fits with other memories, and then "string[s] the ...
beads into different necklaces to be worn as befits the occasion."

When a memory is recalled, it returns to consciousness, so the hippocampus
records it again, expanding and strengthening the original trace. Now, with
multiple traces, the memory is strengthened and preserved.

"Every time we recover a memory, it's re-encoded in the hippocampus," Dr.
Moscovitch said. "So the older the memory, the more chances you have of
recovering it. The more chances you have of recovering them, the more
re-encoding there will be, and the more traces of that memory there will be
in the hippocampus. So there are 'multiple traces.' "

A peculiar consequence of this theory is that memory, while appearing to
recapture the past, in fact can never happen the same way twice.

MEMORY: THE ELEPHANT IN THE ROOM

ECPHORY

Endel Tulving, the prominent Canadian memory researcher, likes to ask his
students to name the two European capital cities that start with the same
two letters and end with the same three letters. It is not a trick question.
They know the answer. They just do not know they know it. "You will have
such a fantastic 'Aha!' experience when you find it," he said.

The question illustrates an important aspect of memory, known as encoding
specificity. It is not only the content of a memory that determines whether
it can be retrieved, but also the context in which it was first entered into
memory. The students know the cities, but it likely never occurred to them
that they share this specific trait. So they are stumped. "There must be
something else that is important for allowing you to think about something
that you know," Prof. Tulving said. "It's not what it is. That's important
too, but also how it is encoded."

This aspect of memory led him to propose a new word, ecphory, for the
process that allows a memory to be drawn into consciousness. Coined by the
late German biologist Richard Semon, Prof. Tulving saw that it fit nicely
with modern memory science. Ecphory is the interaction between a cue and a
trace. In this case, because the cue (the shared letter trait) was not
encoded with the original knowledge of the city names, the cue is useless.
It does not activate a trace. The students know the answer, but they cannot
access it. They have failed to achieve ecphory.

The answer, of course, is the capital cities of Hungary and Romania:
Budapest and Bucharest. But you already knew that. You just did not know you
knew.

Source: Joseph Brean, National Post

MISREMEMBERING

More than a century ago, pioneering psychologist William James said: "Most
people, probably, are in doubt about certain matters ascribed to their past.
They may have seen them, may have said them, done them, or they may only
have dreamed or imagined they did so." The reality that human memory is not
infallible, and rather highly suggestible, is the source of the classic "he
said, she said" in which two people -one right, and one wrong -are equally
convinced of the veracity of their recollections. To misremember, scientists
say, is to mix up bits and pieces of memory events, some of which may have
occurred at different times but which are nonetheless remembered as a single
occurrence. Scientists refer to this as "importation." Misremembrance might
manifest when a person misattributes the source of a memory -for example,
believing he or she read something in the paper when in reality it was
viewed on TV. A person might also misattribute a face to the wrong context,
which occurs when circumstances are incorrectly merged.

Source: Kathryn Blaze Carlson, National Post

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