Summary
When game designers talk about making a game “feel rewarding,” they are — beneath the surface — talking about neurochemistry. Sellers (Advanced Game Design, 2018) provides the most detailed neurochemical model of player engagement in the current body of game design literature, arguing that understanding the brain’s reward systems is not reductive but design-informing: different kinds of game content activate different neurochemical pathways, and a game that targets only one pathway will exhaust it.
This page covers the neurochemical model, the Yerkes-Dodson arousal curve, and the psychological engagement framework it supports. It is a biological complement to Koster’s cognitive/learning model (fun-as-learning) and Csikszentmihalyi’s experiential flow model (flow).
(Sellers, Advanced Game Design, see source-advanced-game-design)
The four primary reward neurochemicals
“These chemicals serve as broadcast signals in the brain that say, basically, ‘whatever is going on right now is good — do more of that!’ However, there is more than one kind of situation that merits a broad ‘do more of that!’ signal, and so we have multiple primary reward neurochemicals.” — Sellers, Ch. 4
| Neurochemical | Common label | Game context |
|---|---|---|
| Dopamine | ”The reward chemical” | Novelty, exploration, goals reached, points going up |
| Serotonin | ”The security chemical” | Levelling up, completing achievements, gaining social status |
| Oxytocin / vasopressin | ”The cuddle hormone” | Social bonding, team play, multiplayer community |
| Norepinephrine / endorphins | ”Stress hormones” | Alertness, concentration, high-tension play |
Dopamine
Dopamine drives alertness, arousal, and motivation to act. It is released in response to:
- Novelty (situations that are new but not too alien)
- Exploration
- Reaching a goal or collecting a reward
“If you have ever felt pleasure just by seeing points going up in a game, that’s dopamine at work.” — Sellers, Ch. 4
Critical property — habituation: Expected rewards are less dopaminergically effective than novel ones. If a reward is expected and not received, dopamine release decreases, making the situation feel actively negative. This is why:
- Predictable reward schedules (e.g. fixed XP per kill) lose effectiveness over time
- Variable reward schedules (e.g. random loot drops) maintain engagement longer — each drop is a potential novel reward
- Players must continue encountering new rewards, mechanics, and challenges if dopamine-based engagement is to persist
Design implication: Build regular novelty into the game. New enemies, new environments, new mechanics, new rewards — each is a dopamine trigger. When the game stops providing novelty, boredom follows.
Serotonin
Serotonin is dopamine’s counterpart — the “stay the course” chemical. It produces feelings of security, satisfaction, and accomplishment. It is released in response to:
- Gaining a sense of safety or security
- Completing an achievement or gaining a skill
- Gaining or confirming social status
“The sense of satisfaction a player feels when levelling up is in part due to serotonin.” — Sellers, Ch. 4
Serotonin-driven engagement is calmer, more stable, and less urgency-driven than dopamine-driven engagement. It is associated with the “outer loop” (slower, more strategic) feel of games — the satisfaction of building something over time, of growing more powerful, of belonging to a community.
The auditory “ding!” of a level-up in MMOs is a conditioned response: it reliably signals the serotonin reward of levelling, making the association stronger over time.
Oxytocin and vasopressin
These neurochemicals govern social bonding and support — ranging from stranger/friend reactions to falling in love. They are released in social encounters and enhance feelings of:
- Belonging to a group
- Trust in team members
- Social engagement and enjoyment
In games, oxytocin-driven engagement is the reason multiplayer is so powerful for retention. Being part of a guild, clan, or team activates the same neurochemical reward systems as real-world social bonding. This is also why games with strong community features retain players far longer than equivalent single-player experiences.
Design implication: Any game mechanic that creates cooperative or social experiences — helping other players, sharing achievements, playing alongside friends — is leveraging this pathway.
Norepinephrine and endorphins
Norepinephrine (noradrenaline) prepares the brain for rapid reaction to stimuli — short-term vigilance, fight-or-flight readiness, and very fast learning under pressure. Endorphins reduce pain and produce energy, especially after strenuous activity.
In games, this pathway is engaged by high-tension, time-pressured situations — the boss fight, the last few seconds of a race, the final moments of a match. These are not the most positive neurochemical states, but they are among the most memorable, and they provide the contrast that makes the serotonin reward of winning those situations especially satisfying.
Design implication: High-tension moments are neurochemically valuable for creating memorable experiences and emotional peaks, but they are fatiguing. Sustained maximum arousal is unsustainable (see Yerkes-Dodson below).
The Yerkes-Dodson arousal curve
The Yerkes-Dodson law (1908) describes the relationship between arousal and performance as an inverted-U curve:
Performance
↑
│ ╭─────────╮
│ ╱ ╲
│ ╱ ╲
│ ╱ ╲
│ ╱ ╲
└──────────────────────→ Arousal
Low Optimal High
(boredom) (anxiety/panic)
- Too low arousal → boredom, inattention, low engagement
- Optimal arousal → peak performance, engagement, and learning
- Too high arousal → panic, cognitive narrowing, performance collapse
This provides a neurophysiological foundation for Csikszentmihalyi’s flow channel: the flow channel is the Yerkes-Dodson optimal zone. The neurochemical substrate of boredom (too little dopamine/norepinephrine stimulus) and anxiety (too much norepinephrine, cortisol) maps directly onto the experiential states Csikszentmihalyi describes.
Design implication: A game’s difficulty pacing should keep the player in the optimal arousal range — not just in terms of challenge (the flow channel framing), but in terms of neurochemical engagement. Sustained maximum tension triggers the stress response; sustained minimum tension triggers the disengagement response.
Psychological engagement: vigor, dedication, absorption
Sellers cites Schaufeli et al.’s (2002) psychological definition of engagement as the experiential correlate of neurochemical engagement:
“Vigor is characterized by high levels of energy and mental resilience while working, the willingness to invest effort in one’s work, and persistence even in the face of difficulties. Dedication is characterized by a sense of significance, enthusiasm, inspiration, pride, and challenge. Absorption is characterized by being fully concentrated and deeply engrossed in one’s work, whereby time passes quickly and one has difficulties with detaching oneself from work.” — Schaufeli et al. (2002), quoted by Sellers
| Property | Neurochemical basis | Game design target |
|---|---|---|
| Vigor | Dopamine + norepinephrine | The game energises rather than drains. Challenge feels surmountable. |
| Dedication | Serotonin + dopamine | The game feels meaningful. Progress feels significant. |
| Absorption | All pathways in combination | The game holds attention completely. Time distorts. |
All three must be present for deep engagement. A game can produce absorption without vigor (passive, effortless scrolling) or vigor without absorption (frantic but disengaging) — but neither constitutes the full engagement state.
Combining the pathways in game design
These pathways are not mutually exclusive — great games engage all four simultaneously, at different timescales:
| Timescale | Primary pathway | Design mechanism |
|---|---|---|
| Moment-to-moment | Dopamine + norepinephrine | Action feedback, score ticking up, kills, hits |
| Session-scale | Serotonin | Level-ups, achievements, unlocks |
| Cross-session | Dopamine (novelty) | New content, new mechanics per session |
| Community | Oxytocin | Guilds, friends lists, co-op, leaderboards |
A game that engages only the dopamine pathway (pure novelty and reward collection) exhausts quickly as habituation sets in. Adding serotonin rewards (slower accomplishment) and oxytocin pathways (social) builds multi-timescale engagement.
Ethics and design responsibility
Sellers briefly addresses the ethical dimension: knowledge of these pathways can be used to create genuinely engaging experiences, or to exploit players (engineered variable reward schedules designed to extract purchases rather than deliver value, near-miss mechanics in loot systems). He leaves the ethical judgement explicitly to the designer.
This is consistent with the broader game design ethics conversation: the neurochemical pathways are mechanisms, not values. The designer’s responsibility is to choose goals that serve the player’s experience, not merely maximise engagement metrics.
Open questions
- The neurochemical model implies that different players may have meaningfully different reward sensitivities (e.g. dopamine sensitivity varies between individuals, and many clinical conditions involve dopamine dysregulation). Should game designers accommodate this variation?
- Variable reward schedules are the most effective dopamine triggers — but are also the mechanism of gambling addiction. Where is the ethical line between engaging game design and addictive design?
- The Sellers model covers the primary reward pathways but does not address cortisol (the primary stress hormone) in detail. How does sustained cortisol elevation (toxic difficulty, punishing failure states) interact with long-term engagement?
Related
- flow — The Yerkes-Dodson curve provides the neurophysiological grounding for the flow channel
- fun-as-learning — Koster’s pattern-learning thesis; dopamine habituation is the mechanism behind “boredom as mastery”
- game-loops — Different loop timescales engage different neurochemical pathways
- game-balance — Keeping players in the Yerkes-Dodson optimal zone is a balance problem
- game-feel — Micro-level feedback triggers dopamine and norepinephrine responses moment-to-moment
- interest-curves — Macro-level pacing of arousal; the curve should track the Yerkes-Dodson optimal range
- systems-thinking — Structural coupling of game+player involves neurochemical feedback
- source-advanced-game-design