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http://en.wikipedia.org/wiki/Brain_stimulation_rewardAlso:
"Reward Substrate Identified by Electrical Brain Stimulation
Olds and Milner (1954) first identified brain sites where direct electrical stimulation is reinforcing. Laboratory animals will lever press at high rates (> 6,000 times per hour) to obtain brief stimulation pulses to certain brain regions. The reinforcement from direct electrical activation of this reward substrate is more potent than other rewards, such as food or water. The potency of this electrical stimulation is most dramatically illustrated in a classic experiment where the subjects suffered self-imposed starvation when forced to make a choice between obtaining food and water or electrical brain stimulation (Routtenberg & Lindy, 1965). A second distinguishing feature of reward from electrical brain stimulation is the lack of satiation; animals generally respond continuously, taking only brief breaks from lever pressing to obtain the electrical stimulation. These two features (i.e., super-potent reward and lack of satiation) are important characteristics of direct activation of brain reward mechanisms.
Initial work suggested that a number of brain regions could produce rewarding effects, but many of these seemingly diverse stimulation sites were quickly linked through a common neural pathway—the medial forebrain bundle (Olds, 1977). Although it is true that activation of other brain systems can produce rewarding effects, activation of the medial forebrain bundle as it courses through the lateral hypothalamus to the ventral tegmentum produces the most robust rewarding effects. And several neurotransmitters may be involved in the rewarding effects from various electrode placements, but dopamine appears to be the neurotransmitter essential for reward from activation of the medial forebrain bundle system (see Fibiger & Phillips, 1979; Wise, 1978). The neuroanatomical elements of rewarding stimulation have been identified using electrophysiological and neurochemical techniques: electrical stimulation activates a descending component of the medial forebrain bundle which is synaptically coupled at the ventral tegmentum to the ascending mesolimbic dopamine system. Rewarding electrical stimulation thus activates a circuitous reward pathway, first involving a descending medial forebrain bundle component and then involving the ascending mesolimbic dopamine pathway (Bozarth, 1987a; Wise, & Bozarth, 1984). The terms mesolimbic and ventral tegmental dopamine system are used interchangeably in this context, both denoting the same dopamine system involved in reward and motivation. "
http://wings.buffalo.edu/aru/ARUreport01.htm
Why does man Kill? He kills for food.
And not only food: frequently there must be a beverage.