Berton and colleagues (2006) found that the regulation of avoidance behavior in mice confronted by an aversive social target requires BDNF (brain-derived neurotrophic factor) from the:

Berton and colleagues (2006) found that the regulation of avoidance behavior in mice confronted by an aversive social target requires BDNF (brain-derived neurotrophic factor) from the: B. vental tegmental area (VTA).

Explanation:

The vental tegmental area (VTA) is located in the midbrain, this section of the brain contanins different type of neurons. This area is in charge of the reward system, that has to do with the reinforcement behavior.  

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and when black people use it, they know that's just how they greet each other

and when white folks use it, they know there's a double meaning under