The evidence behind each dimension

Drive · Inert ↔ Driven

Tendency to initiate activity and to expend effort for reward, absent external demand.

strong dopamine (reward, effort, exploration)

Dopamine agonists can produce impulse-control disorders, and amphetamine raises willingness to expend effort for reward.

Verification: Not verifiable at the individual level; the causal evidence comes from drug manipulation, not from measuring a person's level.

• DOMINION study: impulse control disorders in Parkinson's diseaseImpulse control disorders occur in about 17% of Parkinson's patients taking a dopamine agonist, 2-3x the rate of those not taking one.
• Dopaminergic mechanisms of individual differences in human effort-based decision-makingStriatal and vmPFC dopamine responsivity predicts willingness to expend effort for larger rewards.
• The neuromodulator of exploration: a unifying theory of the role of dopamine in personalityDopamine's general function is to promote exploration, linking it to Extraversion and Openness/Intellect.

Threat reactivity · Unflappable ↔ Highly reactive

How readily and how durably negative emotion is triggered by threat, loss or criticism.

moderate serotonin 5-HT2A

Cortical 5-HT2A binding tracks the inward facets of neuroticism (r = .37, replicated with a second tracer), and SSRIs lower neuroticism beyond their effect on depression.

Verification: No individual-level test. Group-level PET and drug-response evidence only.

• The association between brain serotonin 2A receptor binding and neuroticism in healthy individuals: a Cimbi database independent replication studyCortical 5-HT2A binding is associated with the inward facets of neuroticism (r = .37) in an independent replication.
• Personality change during depression treatment: a placebo-controlled trialParoxetine reduced neuroticism 6.8x as much as placebo among patients matched for depression improvement.

Restraint · Impulsive ↔ Controlled

Capacity to hold to an intention against a competing immediate pull.

strong dopamine (reward-cue)

Dopamine agonists produce impulse-control disorders — gambling, shopping, hypersexuality — in about 17% of Parkinson's patients, reversing on withdrawal.

Verification: Not verifiable at the individual level; the causal evidence is from drug exposure.

• DOMINION study: impulse control disorders in Parkinson's diseaseImpulse control disorders occur in about 17% of Parkinson's patients taking a dopamine agonist, 2-3x the rate of those not taking one.

moderate serotonin (constraint)

Serotonin function correlates inversely with aggression and impulsivity (r ≈ -.12 overall, strongest in pharmacological challenge studies), with tryptophan depletion raising aggression in already-prone individuals.

Verification: Group-level challenge studies only.

• Revisiting the serotonin-aggression relation in humans: a meta-analysisCentral serotonin function correlates inversely with aggression, anger and hostility (r = -.12; -.21 in pharmacological challenge).

Sociality · Detached ↔ Connected

Baseline need for, and reward from, closeness with other people.

preliminary μ-opioid

Cerebral μ-opioid receptor availability tracks adult attachment style, with lower availability associated with avoidant attachment.

Verification: PET, and from a single research group. Treat as a lead, not a finding.

• Adult attachment style is associated with cerebral μ-opioid receptor availability in humansμ-opioid receptor availability tracks adult attachment style; lower availability is associated with avoidant attachment.

Antagonism · Accommodating ↔ Combative

Disposition to pursue one's own interest at others' expense, and to meet friction with force.

moderate serotonin

Central serotonin function correlates inversely with aggression, anger and hostility (r ≈ -.12 overall, -.21 in pharmacological challenge studies), and tryptophan depletion raises aggression specifically in people already prone to it.

Verification: Group-level challenge studies only.

• Revisiting the serotonin-aggression relation in humans: a meta-analysisCentral serotonin function correlates inversely with aggression, anger and hostility (r = -.12; -.21 in pharmacological challenge).

moderate androgen exposure (clinical magnitudes only)

Congenital adrenal hyperplasia and testosterone therapy shift aggression-related measures, but normal-range testosterone does not — a preregistered trial in 1,000 men found no effect on economic behavior.

Verification: Not applicable to normal variation. Included to state explicitly that the popular 'high testosterone' explanation is unsupported.

• Prenatal androgen exposure and sex-typical play behaviour: a meta-analysis of classic congenital adrenal hyperplasia studiesClinical-magnitude prenatal androgen exposure shifts behavior, including physical aggression and tender-mindedness.
• Is testosterone linked to human aggression? A meta-analytic examination of baseline, dynamic and manipulated testosteroneBaseline testosterone correlates with aggression at only r ≈ .07, with no evidence of a causal effect from administration.

Unusual cognition · Conventional ↔ Unusual

Tendency toward unusual perceptions, associations and beliefs, and to act on them. Scored on form and consequence, never on the content of a belief.

strong dopamine (D2)

Antipsychotics act by D2 blockade and amphetamine can induce psychosis — the strongest dopamine-to-trait link anywhere in this research, and on a dimension the original Braverman model never mentions.

Verification: No individual-level test; the inference is pharmacological and group-level.

• The Hierarchical Taxonomy of Psychopathology (HiTOP): a quantitative nosology based on consensus of evidencePsychopathology including the thought-disorder spectrum is distributed dimensionally rather than categorically.
• Predictive validity of psychometrically assessed schizotypy for psychopathology dimensions and functioning in an 8-year multiwave studyPositive and negative schizotypy measured in non-clinical samples predict later symptoms and functioning along distinct paths.

Systemizing · Fluid / social ↔ Systematic / literal

Preference for deriving rules and structure over reading people and context, together with heightened sensitivity to detail and change.

genetic polygenic — no transmitter account

Autistic traits are continuously distributed in the general population and highly heritable, but no clean neurotransmitter story exists. Saying so is part of the point.

Verification: Formal assessment for the clinical end; the trait itself is not confirmable by any biomarker.

• Autism traits dimensionality and multivariate relationship with alexithymia and anxiety in the general populationAutistic traits are continuously distributed through the general population rather than forming a discrete category.
• A comprehensive psychometric analysis of autism-spectrum quotient factor models using two large samplesThe AQ's factor structure is unstable across samples; a reduced multi-factor solution performs best in both community and clinical data.

Episodicity · Steady ↔ Cycling

Degree to which energy, confidence and output arrive in distinct phases rather than at a steady level.

none none claimed

No direct transmitter claim. The scale is justified predictively: the Hypomanic Personality Scale was the single best predictor of later bipolar disorder in a 23-year birth-cohort follow-up (d = 0.67).

Verification: Clinical assessment at the high end; prospective mood charting.

• Predictive and discriminant validity of psychopathology and temperament scales — 23-year follow-up, Northern Finland Birth Cohort 1966High Hypomanic Personality Scale score was the best single predictor of later bipolar disorder (d = 0.67).

Impairment · Unaffected ↔ Severely affected

How much current functioning is affected, whatever the cause. Crossed with every other scale to separate a feature of how someone is built from something that is costing them.

none none

Functional impact is measured directly and carries no biological claim. This scale deliberately does not ask why.