These experiments and observations revealed distinct
differences between classically versus operantly conditioned increase in spike number. Inasmuch as these
differences were observed in the same identified neurons,
they strongly suggest that the mechanisms that produce
the conditioned changes are also distinctly different. The
dynamics of neuronal responses to the CS and DS in our
experiments demonstrate that neuronal analogs of
classical conditioning satisfy the basic properties known
from behavioral experiments. The conditioned response
increased during classical conditioning, decreased during extinction sessions and recovered rapidly during
reacquisition. This was not the case for responses to the
DS, which decreased to a steady level during acquisition
and almost did not change during extinction and
reacquisition. Our data shows that we also developed
a satisfactory neuronal model for instrumental conditioning. The only difference between our neuronal
analog of instrumental conditioning and behavioral
instrumental conditioning is the utilization of an AP in
an identified neuron instead of a motor action. During
training, the animal learned to determine which neuronal discharge was essential for avoiding punishment.
Instrumental conditioning was selective in relation to
both the input (responses to CS vs responses to DS) and the output (responses of a trained neuron vs responses
of a control neuron). A selective increase in the conditioned response compared with responses to the DS
during training is well known (Kandel, 1991). Therefore,
the neuronal activity observed in our experiments may
be considered as representative of the instrumental action of the entire mollusk. Responses during pseudoconditioning changed much more slowly.