People cannot tickle themselves because ticklishness requires unpredictability. In many situations, people enjoy experiencing fear and a lack of control, such as when watching scary movies or riding roller coasters, and people enjoy sex, during which the sympathetic nervous system is activated. The brain has a “pleasure pathway” that connects to the cortex, amygdala, and the ACC, and that predominantly uses dopamine, a neurotransmitter related to pleasure. The most intense pleasure is experienced in anticipation of a reward—the appetitive stage—rather than with the reward, or the consummatory stage. Dopamine encourages pleasure-seeking behavior, but Sapolsky notes that the system is subject to change.

Whether unpredictability is pleasurable or not depends on the context, such as who is involved, how long the experience lasts, and the degree of uncontrollability. Glucocorticoids, when moderately risen, cause a release of dopamine within the brain’s pleasure pathway, but with prolonged exposure to glucocorticoids, dopamine is diminished and dysphoria sets in. Sapolsky posits that those with addictive personality types, including “adrenaline junkies,” might be less sensitive to dopamine, might have higher rises in dopamine levels, or might experience a dip below baseline dopamine levels after the pleasurable experience.