sm by which they facilitate
the study process. We may describe their effects in two ways:
neurologically and psychologically. As may be expected from our
preliminary study of the nervous system, we see their first effects
upon the motor pathways leading out to the muscles. Each passage of the
nerve current from brain to muscle leaves traces so that the resulting
act is performed with greater ease upon each repetition. This fact has
already been emphasized by the warning, Guard the avenues of
expression.

Especially is it important at the first performance of an act,
because this determines the path of later performances. In such studies
as piano-playing, vocalizing and pronunciation of foreign words, see
that your first performance is absolutely right, then as the expressive
movements are repeated, they will be more firmly ingrained because of
the deepening of the motor pathways.

The next effect of acts of expression is to be found in the
modifications made in the sensory areas of the brain. You will recall
that every movement of a muscle produces nervous currents which go back
to the brain and register there in the form of kinaesthetic sensations.
To demonstrate kinaesthetic sensations, close your eyes and move your
index finger up and down. You can feel the muscles contracting and the
tendons moving back and forth, even into the back of the hand. These
sensations ordinarily escape our attention, but they occupy a prominent
place in the control of our actions. For example, when ascending
familiar stairs in the dark, they notify us when we have reached the
top. We are still further impressed with their importance when we are
deprived of them; when we try to walk upon a foot or a leg that has
gone "to sleep"; that is, when the kinaesthetic nerves are temporarily
paralyzed we find it difficult to walk. But besides being used to
control muscular actions, they may be used in study, for they may be
made the source of impressions, and impressions, as we learned in the
chapter on memory, are a prime requisite for learning. Each expression
becomes, then, through its kinaesthetic results, the source of new
impressions, when, for example, you pronounce the German word,
_anwenden_, with the English word "to employ," in addition to the
impressions made through the ear, you make impressions through the
muscles of speech (kinaesthetic impressions), and these kinaesthetic
impressions enter into the body of your knowledge and later