James olds and peter milner (1954) were trying to implant an electrode in a rat's reticular formation when they placed the electrode incorrectly by mistake. curiously, as if seeking more stimulation, the rat kept returning to the location where it had been stimulated by the misplaced electrode. when they realized that they had actually placed the device in a region of the olds and milner realized they had stumbled upon a

hypothalamus; reward center

Explanation:

James Olds and Peter Milner were psychologists who accidentally discovered  the pleasure center in the brain. When experimenting with a rat in McGill University, they realized that they had misplaced the electrode in the rat's brain. Such rat kept pressing the lever so it would discharge such electrodes, up to 2000 times a day, and this is when they realized something else was going on inside the rat's brain. This is how they discovered that the rat was experimenting pleasure as the electrodes were touching the hypothalamus and such area was the reward center.

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