A picture of the learning procedure
1. The bottom-up input causes an initial
state of the code units.
2. This initial state settles to a state that
takes the code energies into account.
3. Then we ignore the bottom-up input and
do a little more settling to get the
To learn the feed-forward connections:
     the settled state is the target output
     the initial state is the actual output.
To learn the lateral connections:
     the energy of the settled state is lowered
     the energy of the final state is raised.