A patient
who was followed for thirty years by the great Soviet neurologist
Alexander Luria had the amazing ability to remember everything.
After looking for a few minutes at pages with 30, 50, or 70 words
or numbers, he could repeat them flawlessly one week, six
months, or even 15 years later, without forgetting a
thing!
Though he was not insane or autistic, this patient was not entirely normal either. Among other things, he experienced synesthesia, which means that he had no boundaries between his various senses. As a result, he experienced some strange associations.For example, he had the unusual ability to associate a colour, sound, or texture with a word or number. This gave him a ready means of creating sensory “hooks” that let him secure words and numbers in his memory permanently.
But this special ability also had some drawbacks. For example, this man had tremendous difficulty in retaining the meaning of a text that he was learning. To answer a simple question about the text, he would have to “re-read” the entire thing in his head! This contrast shows the great power of an ordinary person’s memory, which encodes the meaning first and foremost. In other words, we may forget the exact wording of a story, but we remember its essential elements, which is far more useful in everyday life.
HOW EXERCISING YOUR MEMORY STRENGTHENS IT
Psychologically, forgetting is the temporary or permanent
inability to retrieve a piece of information or a memory that had
previously been recorded in the brain.
Forgetting differs from amnesia in
that forgetting is usually regarded as a normal phenomenon. Also,
forgetting involves specific pieces of content, whereas amnesia
affects a relatively broad category of memories or wipes out an
entire segment of memory.
The chances of your retrieving a memory depend on
many factors, including how well you have been sleeping and how
precisely you labelled this memory in the first place.
Sleep is
a mysterious phenomenon, but one of its roles appears to
be to consolidate the memory traces stored in the brain over
the course of the day.
Thus, in both animals and humans,
an increase in the amount of rapid-eye-movement (REM) sleep
is observed during the night following a learning experience.
Conversely, sleep deprivation adversely affects learning.
Low-frequency sleep, which occurs mainly
at the start of the night, also seems to play a role in consolidating
memories. Some data also suggest that both major phases of
sleep are involved, and that it is the alternation of low-frequency
sleep with REM sleep that produces the beneficial effect.
In
commiting something to memory, just as in any other work, organization is
essential. Two main strategies are available for this purpose:
repetition and elaboration.
In repetition, you take the
piece of information that you are trying to memorize, and
you repeat it continuously, to try to keep it in your short-term
memory, as long as possible.
In elaboration you associate
the new piece of information with other information that
you have already recorded in your long-term
memory. In other words, you incorporate the new fact
into a broader, coherent narrative with which you are already
familiar.
This strategy of elaboration is the
basis for many mnemonic devices methods, some of them very
old, for organizing new information so that you do
not forget it.
Le sommeil, Salvador Dali (1937)
As we grow up, we
all experience various physiological forms of amnesia.
For example, infantile amnesia
is what keeps us from remembering the first three or
four years of our lives. Until children are three or
four, they do not form any genuine episodic memories.
But paradoxically, this is the age when they are acquiring
a great deal of knowledge.
Infantile amnesia is not due solely
to the fact that the first years of our lives are the furthest
back in time. It is also due, at least in part, to the
lack of language and the immaturity of the neocortex and
other structures in the brain.
TYPES OF AMNESIA
There
are several different types of amnesia, but all can be
grouped into two broad categories, according to the type
of trauma that causes them. These two categories are neurological
(or organic) amnesias and psychogenic (or functional) amnesias.
The damage may result from a cranial trauma (a blow to
the head), a cerebro-vascular accident (a burst artery
in the brain), a tumour (if it presses against part of
the brain), hypoxia (lack of oxygen), certain kinds of
encephalitis, chronic alcoholism, and so on.
Psychogenic
amnesias are memory disorders that result from psychological
traumas.
Though these traumas do affect the brain in a certain
sense, patients who suffer from psychogenic amnesia show
no detectable brain injury or brain malfunction.
Instead, the memory loss is caused by some disagreeable
event such as chronic stress, intense fear, rape, incest,
etc.
For older people,
even if they are perfectly healthy, it is normal to have
a bit more trouble remembering events from the last few
days or weeks. This phenomenon chiefly affects long-term
episodic memory and has little effect on working memory.
Thus, older people do not lose
their semantic
memory (though they may be slower at word-identification
tasks) or their procedural
memory (their memory of how to do things),
provided they have the opportunity to maintain the acquired
knowledge through practice.
For though we now know that our stock
of neurons is so large that we can maintain our memory’s
performance to the end of our lives, we also know that
memory needs to be exercised frequently to work properly.
People should therefore keep giving their memory a regular
workout as long as possible.
The most famous patient
in the history of memory studies was known by his initials,
H.M. He was followed for 40 years in Montreal by Dr. Brenda
Milner. To relieve his attacks of epilepsy, doctors had
removed a part of H.M.’s cerebral cortex, including
the hippocampus. The unexpected secondary effect of this
experiment was spectacular: H.M.’s memories of the
episodes of his youth were intact, but he could not acquire
the slightest new long-term memory. People’s faces,
his own actions and gestures–everything disappeared
from his mind in just a few minutes, thus confirming the
major role that the missing part of his cortex had played
in acquiring new memories. Interestingly, his procedural
memory (the kind of “know-how” that
lets someone get better at solving the Hanoi Towers puzzle,
for example) was not affected at all, and this supports
the hypothesis that various memory systems associated with
different physical structures coexist in the human brain.
ANTEROGRADE
AND RETROGRADE AMNESIA
Another distinction
between two major types of amnesia is based on whether
the patient is forgetting past facts or forgetting things
as they happen.
In retrograde
amnesia, patients forget events that occurred in
their lives before they experienced the trauma, and the
oldest facts are the ones least likely to be forgotten.
Recovery is possible, but the events that occurred closest
to the time of the accident are harder to retrieve and
may be lost forever.
Retrograde amnesia is often associated with neurodegenerative
pathologies such as senile dementia and Alzheimer’s
disease. In such cases, the further the disease progresses,
the more the memories of the past dissolve.
Anterograde
amnesia is the inability to memorize new facts, and
hence the inability to learn. Following an injury that
affects Papez’s
circuit, a person becomes incapable of retaining
new facts (explicit
memory). This is sometimes referred to as “forgetting
as you go”.
In this type of amnesia, short-term memory and procedural
memory are preserved, because they are independent
of Papez’s circuit. Affected individuals retain
their skills but not the memory of having acquired
them (since that would involve episodic explicit memory).
Anterograde amnesia often occurs following an acute event
such as a concussion, a heart attack, oxygen deprivation,
or an epileptic attack.
