The medial forebrain bundle (MFB) is an area in the brain. In animals, if an electrode is implanted in this brain structure and small electrical stimulations are given to this site, the animal will start to self-stimulate the area if allowed to do so. The mechanisms behind this self-stimulation are being studied by Dr. Charles Gallistel. The (MFB) self-stimulation phenomenon is a "bridge between brain and behavior". It links behaviorally manifested motivation and information storage processes to activity in a neural pathway descending through the MFB to the midbrain. The stimulation creates a transient motivational state, the priming effect. It also produces a rewarding signal, a neural signal that codes for some motivationally significant facet or facets of the animal's environment. The message carried by this rewarding signal is laid down in memory; it is converted somewhere within the nervous system into an enduring record of the magnitude of the rewarding signal. Together, the transient motivational state and the memory of the rewarding signal dominate the animal's behavior more dramatically than the motivational and rewarding effects of natural variables. The disadvantage of the self-stimulation phenomenon is that it is an artificial phenomenon. The normal function of the stimulated pathways remains ill understood. However, studies suggest that these pathways play a fundamental role in mediating the behavioral effects of naturally occurring nutritional, social and sexual rewarding events and motivating states. The hypothalamus and associated limbic structures are the site where the diverse hormonal and sensory messages crucial to the successful and timely execution of the animal's basic functions (self-preservation and reproduction) are integrated. This integration generates signals that descend to the midbrain, where they determine the course of the animal's behavior by selectively potentiating and depotentiating crucial elements in the neural circuits that establish the basic high-level patterns of coordination. A related function of these parts of the brain is probably the collation of information about substances and situations relevant to basic behavioral goals. Signals carrying this information may be relayed over MFB projections to the sites in the nervous system where this information is stored for use in organizing subsequent goal directed behavior. Thus, while the exact function of the rewarding and motivating pathways excited during self-stimulation may not be elucidated until they have been identified and studied under more natural conditions, it is nonetheless possible to frame well founded hypotheses regarding their general function. The advantage of the self-stimulation preparation from the standpoint of behavioral neuroscience is that highly integrated behavioral effects are produced by direct stimulation of central neural tissue. A vertebrate model will give us extreme access to this motivational system.
