Theoretical background:
A motivational system is required to select goals to be pursued and to organize the animal's commerce with appropriate goal objects. Motivated behavior is usually goal-oriented; the goal may be associated with a drive, such as hunger or thirst. However, the effect of motivation is closely tied to sensory stimuli, e.g., an animal will not usually exhibit eating behavior unless food is present. Moreover, the motivation to eat is not controlled solely by feelings of hunger (when presented with food, animals will often eat in anticipation of hunger and continue to eat after satiation to maintain themselves until the next meal). An external factor, like the sight of food, can play a role in stimulating motivation, and for this reason can be called an incentive. For Toates (1986), motivation arises as a function of both internal state and incentive; a motivational system is one that selects goals to be pursued and organizes the animal's commerce with appropriate goal objects. Motivation played a significant role in many theories of behavior, specially Hull's (1943) theory which proposed that motivation is the initiation of learned, or habitual, patterns of movement or behavior. In Hull's theory, events that threaten survival give rise to internal drive states, and behaviors that reduce the drive are rewarding. In this way, lack of food causes an increase in the hunger drive, and the consumption of food is rewarding because it leads to a reduction in the hunger drive.
Neurally speaking, the basic motivation-related circuitry is located in the hypothalamus. Moreover, the hypothalamus has been divided into functionally related circuitry (subsystems) for eating, drinking, sex, and temperature regulation (Swanson and Mogenson, 1981). The hypothalamus can then be assumed to be the primary place where the information about the internal state of the animal is combined with incentive information, although this role can be shared with other systems. The outcome of such a process would be represented as drives with specific levels.
For more information on motivation and on hypothalamus please refer to the paper cited above or to the papers listed in the Hippocampus and Navigation Group homepage.
Representing drives ...
So far, most models of spatial learning and navigation do not incorporate the role of motivation into their computation. By contrast, the WG theory posits a set of discrete drives to control the animal's behavior. Drives can be appetitive or aversive. The idea is that each appetitive drive spontaneously increases with time towards a maximum value, while aversive are reduced towards 0, both according to a factor intrinsic to the animal. An additional increase occurs if an incentive is present such as the aroma of food in the case of hunger. Drive reduction takes place in the presence of some substrate - ingestion of water reduces the thirst drive.
TAM-WG implements four different drives: hunger, thirst, sex (appetitive), and fear (aversive). Drive levels are represented in the interface by bars. The higher the bar, the higher the correspondent drive level.
In the experiments currently available, only hunger and thirst are used.
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of Southern California Brain Simulation Lab
All contents copyright (C) 1994-1997. University of Southern California Brain Simulation Lab All rights reserved.Author: Alex Guazzelli <aguazzel@rana.usc.edu>