which touch sensation is intact but is usually ignored or not recog-
nized unless one’s attention is specifically drawn to it.Much has been learned about the organization of the somatosensory
cortex by studying mice. Mice depend heavily on their whiskers to
collect information about the world. Their whiskers are constantly
whisking about, coming into contact with nearby objects and pro-
viding a rich source of information about the environment through
which the mouse is moving, even in total darkness. Just as our fingers
and lips have a robust representation in our cortical somatosensory
map, in the mouse brain its whiskers have robust representations in
its somatosensory cortex. Each of perhaps thirty or more whiskers on
each side of the nose sends signal information to specific regions of
the mouse cortex. There is a whisker map in the mouse brain.
What happens if one of a mouse’s whiskers is cut off, or pulled out
in a scuffle with another animal? The cells in the cortex that normally
receive input from the absent whisker will no longer receive signal
input. What happens to those brain cells, now that they seemingly
have nothing to do? Do they sit idle? Do they wither and die?
It turns out they develop neural connections with other nearby
neurons; rather than doing nothing, they now contribute to the
analysis of signals coming in from whiskers next to the one that was
lost. This makes the adjacent whiskers even more sensitive than they
were before. The development of these new neural connections in-
volves new growth and branching of axons and dendrites, as well as
strengthening of connections that were already in place but not much
used. This is an example of neuroplasticity, the ability of neurons to
alter their pattern of connectivity. Neuroplasticity is happening all
the time in the brain, but these neural wiring changes after the loss of
a whisker are a particularly robust illustration.