Hunger researchers initially assumed that the was a brain region responsible for initiating hunger and eating because when it was electrically stimulated, animals would begin to eat?

Lateral Hypothalamus

Explanation:

According to the hunger researchers' initial assumption lateral hypothalamus is that part of the brain which regulates intake of food and metabolical activities like metabolical regulation of peptides like  the orexins melanin-concentrating hormone. It is that part of the brain that plays a key role in the ingestive behavior regulation.

The lateral hypothalamus system initiates physical and cognitive processes like it promotes arousal and feeding behavior, metabolism, regulates body temperature, BP, etc. and when stimulated it results in the feeding behaviour in animals as they begin to eat.

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