1. Registration: The type of information you're receiving
determines which region of your brain is active. For
example, words are initially processed in the language
regions of the brain, pictures initially in the visual
regions. This is where your memories are “registered.”
2. Immediate memory: When information comes into a
region, it comes in as a pattern of nerve cell activity.
This nerve cell activity normally persists for just
a short period of time - seconds or less. This is of
course what we deem “Immediate” memory
3. Permanent (long-term) memory: If the information
in this temporary pattern of activity is to be permanently
stored (and most is not) it will be saved within the
same regions of the brain. Saving the patterns of activity
consists of changing nerve cell connections so that
the pattern of activity can be called forth again, at
some later time. To do this, some nerve cell connections
are strengthened, while others may be weakened. These
changes are relatively permanent, although the changes
may take weeks or months to completely solidify.
Even though the solidification occurs in the regions
of the brain that contained the original activity, the
signal to make the solidification occur came from other
regions. The best known of these regions with such signaling
functions are the hippocampus and the thalamus. The
hippocampus is on the inner side of the temporal lobe;
the thalamus is located deep within the center of the
brain.
4. Memory access: Remembering what you've learned may
be a simple matter of just reactivating a latent memory
- for example, by seeing a picture again and recognizing
it as familiar. In this case, the memories get reactivated
in the region of the brain where they were first stored.
The measurement of familiarity - the sense of how familiar
something is, or how recently you learned it - seems
to be done in parts of the temporal lobe, particularly
in or near a structure called the amygdala, which sits
just in front of the hippocampus.
This simple memory retrieval operates very quickly.
You can decide that a picture is familiar to you or
not in less than one-half a second, measuring from the
very start of the time you see the picture to the start
of when you say "yes" or "no." Once
the picture has been registered in your brain (which
takes about two-tenths of a second), it takes you about
two-tenths of a second to actually make the decision,
and about another two-tenths of a second to say your
answer. The total time it actually takes you is a little
less than the time you spend on each stage, because
some of these stages can overlap. You start deciding
a picture is familiar or not while the image of the
picture is still developing within your mind.
