Normally, dopamine signals positive outcomes. However, in extreme survival states like starvation, its function inverts to signal punishment prediction errors. This powerfully reinforces learning about and avoiding threats rather than seeking rewards, ensuring survival takes precedence over all other goals.

The brain maintains balance by counteracting any deviation to the pleasure side with an equal and opposite reaction to the pain side. This opponent process is why we experience hangovers and why chronic indulgence leads to a dopamine deficit state, driving us to use more just to feel normal.

Neuroscience shows pleasure and pain are co-located in the brain and work like a seesaw. When we experience pleasure, the brain immediately compensates by tilting towards pain to restore balance. This neurological 'come down' is why constant pleasure-seeking eventually leads to a state of chronic pain and craving.

Dopamine is often misunderstood as a 'pleasure molecule.' Its more crucial role is in motivation—the drive to seek a reward. Experiments show rats without dopamine receptors enjoy food but won't move to get it, starving to death. This seeking behavior is often triggered by the brain's craving to escape a dopamine deficit state.

SSRIs block serotonin reuptake, but excess serotonin spills over and is absorbed by dopamine transporters. This effectively puts the "negative/waiting" signal (serotonin) into the "positive/reward" pathway. This mechanism may explain the anhedonia, or blunted pleasure, that some patients experience on these medications.

Most believe dopamine spikes with rewards. In reality, it continuously tracks the difference between your current and next expectation, even without a final outcome. This "temporal difference error" is the brain's core learning mechanism, mirroring algorithms in advanced AI, which constantly updates your behavior as you move through the world.

The brain needs a way to compare the value of disparate items like food, money, or social status. Dopamine serves as this common currency. It creates a standardized value signal, allowing the brain to make decisions and allocate effort across different domains by translating everything into a single, comparable scale.

Neuroscience shows that forward physical movement during periods of high alertness or stress activates a brain circuit that releases dopamine. This not only provides a sensation of reward in the moment but also neurologically reinforces the motivation to approach similar challenging goals in the future.

The feeling of dissatisfaction after achieving a major goal is a feature, not a bug. The brain's dopamine system is designed to keep you moving forward. If any single achievement—a partner, a food, a drug—were permanently satisfying, the drive to live and procreate would cease. The system ensures you always have another place to go.