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Memory loss, also known as amnesia, is
a state of unusual forgetfulness. It can be caused by brain damage
resulting from diseases, such as Alzheimer’s and Huntington’s. It
may result from an injury or severe emotional trauma. The normal
aging process may lead to slower recall of information and greater
difficulty in learning new material. In itself, however, aging will
not dramatically affect one’s memory.
Memory involves several different
functions of the brain. Most students of the brain divide memory into
two kinds, declarative and procedural. The procedural involves skills
and habits. The declarative, on the other hand, involves storing
facts. Memory processes can be itemized according to the time they
take: very short-term memory, which lasts about 100 milliseconds;
short-term memory, which is of a few seconds’ duration; working
memory, which stores recent experiences; and long-term memory, which
houses verbal material that has been rehearsed and motor skills that
have been practiced.
One possible
explanation of long-term memory is that it starts with activity in
the front part of the brain. The information chosen for long-term
memory passes as an electrical impulse to a part of the brain known
as the hippocampus. Here a process called long-term potentiation
enhances the neurons’ ability to pass messages.
A different theory
of memory stems from the idea that brain waves play a key part. Its
proponents believe that regular oscillations of the brain’s
electrical activity, rather like the beat of a drum, help bind
memories together and control the moment at which different brain
cells are activated.
Researchers believe that the brain
stores different aspects of memories in different places, each
concept being linked to the area of the brain that specializes in
perceiving it. Some parts of the brain certainly contribute to
memory. The amygdala, a small almond-size clump of nerve cells close
to the brain stem, processes memories of fear. The basal ganglia
region is focused on habits and physical skills, and the cerebellum,
at the base of the brain, concentrates on conditioned learning and
reflexes. Here, it is believed, we store the skills of balance—for
example, those we need to ride a bicycle.
The following types of amnesia have
been recognized:
Transient global amnesia, which is
a temporary complete loss of memory
Anterograde amnesia, which refers
to the inability to recall recent events in the aftermath of a
trauma
Retrograde amnesia, which is the
inability to remember events preceding a trauma. Recall of events
after the trauma, however, is unaffected.
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