An insect preparation, in which the frequency of discharge of an identified tonic motoneurone can be modified by operant-conditioning, is recommended as a model for a study of cellular neuronal events underlying learning. To facilitate the study of the underlying events, we have developed computer programs for on-line control of training. The discharge pattern of the neurone is analysed continually, trends in mean frequency being recognized automatically. Experiments were conducted on a large number of locusts with the perfected computer programs. Statistically significant shifts are used to trigger the delivery of aversive electric shocks to the preparation. In the increase mode, shocks were correlated with spontaneous decreases in frequency. These were followed, in 68% of preparations, by a stable increase in mean frequency (up-learning) that averaged 140.0%. In the decrease mode, shocks were correlated with spontaneous increases in frequency. These were followed, in 64% of preparations, by a decrease in frequency (down-learning) that averaged 62%. Experimentally raised or lowered frequencies were maintained for periods up to a few hours without, and longer with, reinforcement. The trends could be reversed by applying the reciprocal computer program.