of these things at all, yet the truth remains as before: for the particular mind
which remembers these things, the facts did not exist while they were out of the
mind.
It is not the remembered fact which is retained, BUT THE POWER TO REPRODUCE THE
FACT WHEN WE REQUIRE IT.
The Physical Basis of Memory.—The power to reproduce a once-known fact
depends ultimately on the brain. This is not hard to understand if we go back a
little and consider that brain activity was concerned in every perception we have
ever had, and in every fact we have ever known. Indeed, it was through a certain
neural activity of the cortex that you were able originally to know that Columbus
discovered America, that your house is white, and that it rained on a day in the
past. Without this cortical activity, these facts would have existed just as truly,
but you would never have known them. Without this neural activity in the brain
there is no consciousness, and to it we must look for the recurrence in
consciousness of remembered facts, as well as for those which appear for the
first time.
How We Remember.—Now, if we are to have a once-known fact repeated in
consciousness, or in other words remembered, what we must do on the
physiological side is to provide for a repetition of the neural activity which was
at first responsible for the fact's appearing in consciousness. The mental
accompaniment of the repeated activity is the memory. Thus, as memory is the
approximate repetition of once-experienced mental states or facts, together with
the recognition of their belonging to our past, so it is accomplished by an
approximate repetition of the once-performed neural process in the cortex which
originally accompanied these states or facts.
The part played by the brain in memory makes it easy to understand why we find
it so impossible to memorize or to recall when the brain is fatigued from long
hours of work or lack of sleep. It also explains the derangement in memory that
often comes from an injury to the brain, or from the toxins of alcohol, drugs or
disease.
Dependence of Memory on Brain Quality.—Differences in memory ability,
while depending in part on the training memory receives, rest ultimately on the
memory-quality of the brain. James tells us that four distinct types of brains may
be distinguished, and he describes them as follows:
Brains that are: