The amygdala is a key brain structure in the limbic system. Those who experience brain damage in this area have difficulty developing conditioned fear responses.

Drive reduction theory is based on the idea that human behavior is motivated by various drives. This behavior is undertaken in hopes of reducing the state of tension these drives create. The most basic of examples would be that when people are hungry they experience the distress of hunger and are motivated to look for food. A more nuanced example might be humans' drives to connect with romantic partners. If humans seek connection and don't find it with one partner, they may look for it in another person.

Extrinsic motivation is a pervasive force behind many of our daily behaviors. Most people don't go to work because it's intrinsically pleasurable, but because they need something. In essence, extrinsic is when someone does something for something else. We go to school to avoid punishment and get approval from our teachers, parents, and peers. We work to get money to pay the bills to avoid being broke and to make our families happy and comfortable. 

The reverse is doing something for its intrinsic pleasure, known as intrinsic motivation. For instance we may enjoy knowing more about the world for the pleasure it gives us, not what we have to gain from it.

Emotions are a product of evolution designed to signal when humans need or want something or when a certain need or want has been met. Emotions are universal, as they can be observed cross-culturally, though the degree of expression of emotion may vary in different cultures. 

Gherlin is secreted by an empty stomach and tells the brain to switch hunger on. Leptin is secreted by fat cells and tells the brain to switch hunger off. Serotonin is a neurotransmitter associated with feelings of well-being.

Primary drives refer to things a person needs to survive, like thirst and hunger. Secondary drives are determined by social factors, money, pride, and fame are all great examples of secondary, not primary, drives.

The Yerkes-Dodson law is a curve known for its bell shape, relating its independent variable (i.e. arousal) to its dependent variable (i.e. performance). This graph shows that performance peaks at moderate levels of arousal, as high levels of arousal result in stress while low levels of arousal result in boredom. 

Downward social comparisons are defense mechanisms that present when people seek to preserve or defend their self-esteem. These mechanisms come in the form of comparing oneself to others who are worse off—less successful, less happy, or less fortunate.

The affiliation motive is a need to be involved with others. This need is heightened when people feel like celebrating or feel anxious.

Personal satisfaction is an example of intrinsic motivation, since it is driven by internal rewards.