Brain neuronal mechanisms of motivation and reinforcement: systemic organization of behavior.

The concept of systemic quantitation of behavior was used to study the interaction between dominant motivation and reinforcement on brain neurons. Feeding and escape were used as experimental models. Results showed that feeding and escape motivations are based on the mechanisms of ascending activating influences of lateral or ventromedial hypothalamic centers, respectively, on cortical neurons. Feeding and escape motivations evoked by electrical stimulation of hypothalamus, or the ones occurring naturally, modify the responses of single neurons of sensorimotor and insular cortex to sensory stimuli, to microiontophoretic application of neurotransmitters and neuropeptides, and especially to reinforcement. Dominant motivations are reflected in the burst-like activity and in a specific pattern of interpulse intervals of single units in various brain structures. Reinforcement transforms this activity into a regular pattern and also changes the neuronal responses of hypothalamic feeding and escape centers, to electrical stimulation and to microiontophoretic application of oligopeptides. Specific patterns of the unit responses to conditioned stimuli in the course of consecutive reinforcement was determined. After several instances of reinforcement, especially after repetitive reinforcement, the brain neurons influenced by the dominant motivation begin to produce specific protein molecules that are important for organization of an appropriate type of behavior. This process can be blocked by protein synthesis inhibitors.