Neuron activity in the pedunculopontine nucleus during an operant conditioned defensive reflex.

The activity of 109 neurons in the compact and diffuse zones of the pedunculopontine nucleus was studied in freely mobile rabbits during the acquisition and performance of a defensive operant conditioned reflex. A total of 47% of the neurons recorded showed responsive properties to the conditioned stimulus, which is evidence for the involvement of the pedunculopontine nucleus in operant learning. A significant predominance of excitatory conditioned reflex responses to the conditioned stimulus was demonstrated, showing that the nature of the influence of the pedunculopontine nucleus on projection structures during learning is mostly excitatory. The main patterns of cell responses to the conditioned stimulus were identified, these reflecting the nature of the influence of the conditioned stimulus on neuron activity, the structure of the behavioral act, and the properties of the reinforcement, suggesting a relationship between the pedunculopontine nucleus and the processes of attention, motor learning, and reinforcement. A significant decrease in the reactivity of neurons in the pedunculopontine nucleus to the conditioned stimulus as a result of specialization due to learning was demonstrated. Differences in the associative reactive properties of the compact and diffuse zones of the pedunculopontine nucleus to the conditioned stimulus were identified, which is evidence for the functional heterogeneity of this formation and suggests a leading role for the cholinergic compact zone in operant defensive behavior.