Jeffrey Gray’s Factorial-biological Theory of Personality

You’re standing at the edge of a crowded room with a drink going warm in your hand. One part of you wants to cross the floor and say hello to the person laughing near the window. Another part has already composed three reasons to stay put. Your stomach tightens, your attention narrows, and the conversation you haven’t had yet starts replaying in your head. Which part is “really” you? According to Jeffrey Gray’s theory of personality, both, and the argument between them is the point.

Gray, a British psychologist and neuroscientist, proposed that personality grows out of brain systems that respond to reward, to threat, and to conflict between the two. People differ in how strongly those systems fire. A person whose reward system runs hot looks bold and restless; a person whose conflict system runs hot looks cautious and worried. Many popular summaries flatten this into “introverts are anxious, extraverts are impulsive,” which gets the geometry slightly wrong and the biology badly wrong. The real picture is more interesting: three systems, one of which exists mainly to referee arguments between the other two, each tuned a little differently in every person you know, which is why two people can face the same party, the same job offer, and the same awkward silence, and walk away with opposite stories.

It’s a theory about motivation, not labels.

This article explains Jeffrey Gray’s factorial-biological theory of personality, now called reinforcement sensitivity theory: where it came from, what the three systems do, why a 2000 revision split fear from anxiety, how researchers measure them, and where the evidence is shakier than textbooks admit.

What is Jeffrey Gray’s biological theory of personality?

Reinforcement sensitivity theory (RST) is a neuropsychological account of personality, proposed by Jeffrey Alan Gray, which holds that stable differences between people come from how sensitive their brain systems are to rewards, punishments, and conflicts between the two. It is the theory behind the familiar abbreviations BIS and BAS.

The “factorial” part of the name refers to its roots in factor analysis, the statistical method used to boil many questionnaire items down to a few underlying dimensions. The “biological” part refers to Gray’s insistence that those dimensions should be tied to identifiable brain circuitry and to animal research, not just to the way people answer surveys. Gray started from questionnaire-derived dimensions and asked what they might be made of.

His central move, published in 1970, was to argue that the anxiety and impulsivity dimensions were more biologically meaningful than the broader trait labels psychologists used at the time. Anxiety, in his view, reflects sensitivity to signals of punishment. Impulsivity reflects sensitivity to signals of reward. That sounds tidy; in practice, it opened a long argument about how many systems exist and what each one does.

Picture Marguerite, 34, who takes a new job in a different city. She’s thrilled by the salary and the freedom, and she can’t sleep for dread. In Gray’s terms, her reward system is pulling her toward the move while her threat and conflict systems are working overtime. Neither response is a flaw; the combination is simply how her particular nervous system weighs the odds.

Gray developed the theory across decades, in his 1982 book The Neuropsychology of Anxiety, then in a heavily revised second edition with Neil McNaughton in 2000. The revision changed which system does what, and many websites still describe the older version. We’ll untangle both below.

Some warning labels first. RST is a theory of individual differences in motivation, not a diagnostic tool, and scoring “high BIS” on a questionnaire doesn’t mean you have an anxiety disorder. It’s also a theory still under active debate. Researchers disagree about how many systems exist, how cleanly they map onto brain regions, and how best to measure them in humans.

Why does it still matter? Because few personality theories ask the question Gray asked: what is each trait for, and what part of the brain is doing the work?

How did Gray build on Hans Eysenck’s personality model?

Gray took the two big dimensions in Hans Eysenck‘s model, extraversion and neuroticism, and rotated them by roughly 30 degrees to produce new axes he called anxiety and impulsivity. He argued that the rotated axes lined up better with how animals learn from reward and punishment.

Some background helps. Eysenck, a German-born British psychologist, described personality using a handful of broad dimensions: extraversion, neuroticism, and later psychoticism (the PEN model). In The Biological Basis of Personality (1967), he proposed that extraversion relates to the arousal level of the brain, so that introverts are chronically more aroused and extraverts less, and that neuroticism relates to emotional reactivity in the limbic system. The idea was bold, testable, and partly wrong, which is a decent description of most good theories.

Gray’s objection was a geometric one. If you take Eysenck’s two axes as a graph, a person who is both neurotic and introverted sits in one corner, and a person who is neurotic and extraverted sits in the opposite one. Gray suggested that a more natural way to cut the same graph was along the diagonals. One diagonal would run from stable-extraverted to neurotic-introverted and capture anxiety. The other would run from stable-introverted to neurotic-extraverted and capture impulsivity.

The rotation is not a trick; it’s a different way of slicing the same data, and the difference matters only if one slicing connects better to biology. Gray believed his did, because he could link it to animal experiments on punishment, reward, and anti-anxiety drugs.

Consider two colleagues, Tomas, 41, and Aiko, 29, both rated as highly emotional by a standard questionnaire. Tomas withdraws from meetings after criticism and replays it for days. Aiko storms into the next meeting with three new proposals. Eysenck’s scheme sees them as different on extraversion. Gray’s scheme sees two different kinds of emotional reactivity, one tied to threat sensitivity and one to reward sensitivity.

The evidence, honestly, is mixed. The rotated axes have been hard to confirm cleanly in questionnaire data, and later versions of RST dropped the explicit link to Eysenck’s graph in favor of separate, brain-based systems. The rotation is best understood as the bridge that carried Gray from factor analysis into neuroscience.

What does the behavioral inhibition system actually do?

The behavioral inhibition system (BIS) is the brain system Gray proposed to detect conflict and uncertainty, pause ongoing behavior, increase attention to possible danger, and produce anxiety. Its job is to make you stop and check before you act, especially when both approach and avoidance look tempting.

That definition comes from the revised theory. In the original version, the BIS was described as a system sensitive to punishment, non-reward, and novelty. Gray built much of the case from studies in which anxiety-reducing drugs altered how animals behaved when they faced exactly those signals, which suggested a shared circuit. The circuit he pointed to centered on the septo-hippocampal system, along with the amygdala and connected cortical regions.

In the revised version, the BIS is better described as a conflict-resolution system. It switches on when you want something and fear something at the same moment, or when two attractive options or two threatening options compete. Then it slows you down, scans the environment, and keeps you alert while you gather information.

Researcher Philip J. Corr, one of Gray’s most influential successors, has linked BIS activity at the level of experience to worrying, rumination, and a sense of possible danger or loss. That helps explain why high BIS sensitivity shows up as the person who rereads an email five times before sending it, or who replays a conversation at 3 a.m. looking for the sentence that went wrong.

The system is useful, not defective. A well-tuned BIS stops you from quitting a job on impulse or texting an ex at midnight. A hypersensitive one can stall decisions in a loop of “what if.”

Here’s a plain example. Rafael, 52, is offered an early-retirement package. The money would let him finally build the workshop he’s always wanted, and leaving would also cost him the only structure his days have. Both sides are strong. For a few weeks, he can’t decide, sleeps badly, and keeps asking his family the same questions. That stretch of stalled, vigilant uncertainty is what the BIS is for.

The caveats are real. Much of the BIS evidence comes from animal work, and mapping a conflict system onto human worry involves inference. Questionnaires that measure “BIS” in people mostly capture general anxious tendencies. Calling that scale score a direct reading of a brain circuit overstates what we know.

A practical takeaway for the highly cautious reader: when you feel stuck, ask whether the conflict is real or imagined. If two real goods are colliding, hesitation is the BIS doing its job.

How does the behavioral approach system drive impulsive, reward-seeking behavior?

The behavioral approach system (BAS) is the system Gray proposed to move you toward rewards. It responds to cues that signal something good is available, energizes pursuit, and produces positive feelings such as hope, excitement, and eagerness. Strong BAS sensitivity is linked to impulsivity and reward-seeking.

Many people assume more reward drive is automatically a strength, and others assume it’s a recipe for trouble. Neither holds up. Reward sensitivity helps explain why some people start projects, chase promotions, and approach strangers without much hesitation. It also helps explain why some people bet more than they can afford or abandon plans when something shinier appears.

The name has a small history. Gray first called it the behavioral approach system; psychologist Don C. Fowles later suggested “behavioral activation system,” and both labels now circulate. Fowles was one of the early researchers to connect Gray’s ideas to psychophysiology, including heart rate and electrodermal activity, and to psychopathy.

In the revised theory, the BAS responds to all appetitive stimuli, whether learned or unlearned. That broadened the original idea, which had focused on conditioned cues. The BAS is also now treated as multidimensional: researchers distinguish between reward responsiveness (the pleasure of anticipated reward), drive (persistent goal pursuit), and fun-seeking (a readiness to pursue novel, rewarding things on impulse).

Think of Imran, 26, who finds out on a Thursday that a friend is driving to the coast on Saturday. By Friday morning, he’s rented a tent, texted five people, and rearranged a shift. Not everyone’s brain behaves like this, and Imran’s isn’t “wrong”; his approach system simply fires fast and hard.

Research links BAS sensitivity with extraversion, impulsivity, and positive emotion, though the associations vary across studies and scales. It’s also been explored in relation to substance use, risky behavior, and some mood conditions, but these links are correlational. Nobody should read a high-BAS profile as destiny.

The limits deserve mention. The BAS is a theoretical construct tied to dopamine-rich reward circuitry in animals, and the human picture is far messier. Reward pursuit also depends on context, culture, and learning, which a personality dimension can’t capture.

Practical takeaway: if you recognize a strong approach tendency in yourself, build a short delay into big decisions. Write the plan down, sleep on it, and check whether the excitement survives the morning.

What is the fight-flight-freeze system, and how is fear different from anxiety?

In the revised theory, the fight-flight-freeze system (FFFS) is the brain system that responds to threat itself. It drives escape, defensive aggression, or freezing, and it underlies fear. Anxiety, by contrast, belongs to the BIS and arises when the threat is uncertain or conflicts with a goal.

That split is the revision’s most important contribution. Early RST lumped all negative emotion into one punishment-sensitive system. Neil McNaughton and Gray argued, using findings on how different drugs affect different defensive behaviors, that fear and anxiety have separate circuits and separate jobs. With Philip J. Corr, McNaughton later developed the idea of “defensive distance“: when a threat is close and clear, the FFFS drives avoidance; when a threat is possible but not present, the BIS drives cautious approach and risk assessment.

A short scene makes this concrete. Dalia, 38, is walking to her car when a dog lunges from behind a fence. She jumps backward and her heart slams. That’s the FFFS: quick, bodily, over fast. Twenty minutes later, she’s still checking behind her, running the route in her head, and wondering whether to walk a different way tomorrow. That’s the BIS taking over with the leftover uncertainty.

Which response you show matters, too. The FFFS is described as producing fight, flight, or freezing depending on the circumstances, such as how close the threat is and whether escape is possible. Researchers have linked FFFS function to panic and to phobic fear, although those links are still being tested.

The distinction has clinical appeal. Treatments for phobias often work by exposing people to a feared object until the FFFS response fades, whereas treatments for worry-based anxiety often focus on tolerating uncertainty. That parallel is suggestive, not proof that the two systems explain the treatments. Therapies like exposure were developed independently of RST.

The weak point is measurement. The FFFS is difficult to assess with ordinary questionnaires, and many studies simply haven’t measured it. Some researchers propose subscales or new scales to capture fear sensitivity, with promising but early results.

Practical takeaway: when you feel afraid, ask whether the threat is present or merely possible. A present threat needs action. A possible one often needs information.

How did the 2000 revision change reinforcement sensitivity theory?

The 2000 revision by Jeffrey Gray and Neil McNaughton changed three things: the BIS became a conflict-detection system rather than a punishment system, the FFFS took over responses to threat, and the BAS broadened to cover all rewarding stimuli. A 2004 update by McNaughton and Philip Corr refined the logic using defensive distance.

The simplest way to see the shift is a side-by-side comparison.

Why change anything? Because evidence kept piling up that didn’t fit. Anti-anxiety drugs, for instance, affected some defensive behaviors but not others, which hinted that “punishment sensitivity” was bundling two different things. The revised version aimed to match the neuroscience better, even at the cost of a more complicated story.

Philip J. Corr‘s 2004 review helped carry the revised theory into human personality research, spelling out how the three systems might relate to traits like extraversion, impulsivity, and anxiety. Subsequent work edited by Corr in 2008 gathered the evidence into a single volume, a useful checkpoint for the field.

A fair warning: the revision created a messy gap between theory and practice. Many studies still cite the original BIS definition while using questionnaires built on it, so “BIS” in a research paper may mean different things depending on the year. When you read about RST online, check whether the page distinguishes the two versions.

The revised theory is also harder to falsify, which critics dislike. If a system can be activated by several kinds of input, almost any finding can be explained after the fact. Predictions are still possible, but they need careful design.

Practical takeaway for readers: treat the original BIS/BAS vocabulary as a handy shorthand, and the revised version as the better picture of what the brain is thought to be doing. When a source says “BIS equals punishment sensitivity,” it is describing the older model.

How are BIS and BAS measured, and what do the scales really show?

Researchers most often measure BIS and BAS with the BIS/BAS Scales, a 20-item self-report questionnaire created by Charles S. Carver and Teri L. White in 1994. Respondents rate statements on a four-point scale, and the scores are split into one BIS scale and three BAS subscales.

Carver and White built the scales to capture dispositional sensitivity to Gray’s two systems. In their studies, people who scored high on BIS sensitivity felt more nervous when they anticipated punishment, and people who scored high on BAS reward responsiveness and drive felt happier when they anticipated reward. Those predictions held better than those of an alternative measure the authors compared, which is why the scales became so widely used.

• BIS (7 items): reactions to the anticipation of punishment, such as worry about making mistakes.
• BAS Reward Responsiveness (5 items): positive responses to the occurrence or anticipation of reward.
• BAS Drive (4 items): persistent pursuit of desired goals.
• BAS Fun Seeking (4 items): willingness to pursue new rewards on impulse.

Reliability was acceptable in the original paper. The internal-consistency figures for the four factors ranged from about .66 to .76, with Fun Seeking the lowest. That is adequate for research on groups and not a precise tool for judging an individual.

The limits are significant. The scales were built before the 2000 revision, so they measure the older BIS, which mixes anxiety-like worry with punishment sensitivity. They also don’t directly measure the FFFS. Newer instruments and adapted versions try to capture fear separately, and early results are promising, but nothing has settled the matter.

Self-report adds its own distortions. People differ in how they interpret items, and mood on the day can color responses. Scores also say nothing about the brain. A high BIS score tells you how someone describes themselves, not what their septo-hippocampal system is doing.

Take Priyanka, 23, who completes the scales for a university psychology study and scores high on BIS and moderate on BAS. The researchers would describe her as sensitive to punishment cues and average in reward drive. They wouldn’t say she’s anxious or that she’ll struggle in her job.

Practical takeaway: if you take an online version, treat the result as a prompt for reflection about how you respond to risk and reward. It isn’t a diagnosis, and a high score doesn’t call for treatment on its own.

What does Gray’s theory say about anxiety, depression, and impulsive behavior?

RST proposes that overactive BIS sensitivity raises vulnerability to anxiety, that weak BAS functioning may relate to low motivation and mood problems, and that strong BAS sensitivity may relate to impulsive and risk-taking behavior. These are hypotheses with partial support, not established causal explanations.

Start with anxiety. Because the BIS handles conflict and uncertainty, a hypersensitive BIS could produce a lot of worry and a tendency to see ambiguous situations as threatening. Studies using the Carver and White scales generally find that BIS scores correlate with self-reported anxiety and with symptoms of generalized anxiety and social anxiety. That is a correlation, and it could partly reflect overlap in the questions asked.

Depression is murkier. Some researchers propose that reduced BAS activity could dampen motivation and the pleasure of anticipating rewards, which resembles loss of drive in depression. Others point out that high BIS also correlates with depressive symptoms, so the two systems may combine. The pattern isn’t consistent enough to say that either profile predicts depression.

Impulsivity and substance use bring the BAS back in. High reward sensitivity has been linked with a greater likelihood of risk-taking, heavy drinking, and some forms of gambling in several studies. Yet most people with high BAS never develop problems, and many with problems don’t have high BAS. Circumstances, upbringing, stress, and access to substances matter a great deal.

A composite example: Wen, 45, has long been a worrier. When her teenage son started driving, her sleep fell apart and she kept checking his location. A therapist might describe this in everyday terms as a strong tendency to anticipate danger, and might help her practice tolerating uncertainty. RST would add a speculative layer: a sensitive conflict system, firing at every small uncertainty.

It’s tempting to turn these ideas into labels such as “BIS person” or “BAS person.” Resist that. Most people have moderate scores on each system, and the pattern shifts with life stage and context. Using the theory to excuse or pathologize behavior goes beyond the evidence.

When should you look for help? If worry, low mood, or impulsive behavior is disrupting sleep, work, relationships, or safety, speak with a licensed therapist, psychologist, or primary care doctor. Personality theory can add context to that conversation, but it isn’t a substitute for an assessment.

What should readers do with all this? Use it to ask better questions, not to settle old ones.

What are the main criticisms and limits of reinforcement sensitivity theory?

The main criticisms are that the theory rests heavily on animal research, that its human measures are imperfect, that the revised version is harder to test, and that links to clinical conditions are largely correlational. None of these makes RST wrong; they set limits on how far it can be pushed.

Start with translation from animals to humans. Gray’s evidence on the septo-hippocampal system and defensive behavior came from rats and other animals. Human anxiety involves language, self-reflection, and social meaning that rats don’t share. Brain imaging studies have tested parts of the theory in people, with mixed results, partly because the circuits involved are small and hard to isolate.

A second issue is measurement. The best-known questionnaire pre-dates the revision, and newer scales haven’t yet displaced it. As a result, the theory that researchers write about and the theory they measure are often slightly different things. Philip J. Corr and others have acknowledged this tension openly, and work on better instruments continues.

Then there is overlap with other models. The Big Five trait model already contains extraversion and neuroticism, which look similar to approach and avoidance tendencies. Critics ask what RST adds beyond a new vocabulary. Defenders answer that its value lies in biological hypotheses and in predictions about learning and conflict, which trait models don’t make.

Several practical limits follow:

• Scores describe tendencies in groups, not the brain activity of a single person.
• Correlations between BIS or BAS and clinical symptoms don’t show cause.
• Much of the evidence comes from university students in Western countries, so generalizing is risky.
• The revised theory allows flexible explanations, which makes clear falsification difficult.

Consider Joseph, 60, a retired engineer who reads about the theory and decides his difficulty with spontaneity is his “weak BAS.” It’s a neat explanation. It’s also an unverified label applied to a complicated life. A more careful reading would say that he may be cautious, that this has costs and benefits, and that he can experiment with small risks.

Honest summary: RST is a productive framework, not a settled map. It earns its place by generating testable ideas about fear, anxiety, and reward, and by tying personality to neuroscience. It loses ground whenever someone treats a questionnaire score as a window into a circuit.

That’s a reasonable standard for any theory of personality.

How can you use Gray’s theory in everyday life?

You can use Gray’s theory as a reflection tool for noticing how you respond to opportunity, risk, and uncertainty, and for adjusting how you make decisions. It won’t tell you who you are, but it can sharpen the questions you ask when you feel pulled in two directions.

Begin with a simple observation habit. Over a week, note moments when you felt a strong pull toward something and moments when you felt a strong urge to hold back. Notice what came first, whether the pull was toward a reward or away from a threat, and whether the two collided. Patterns tend to show up quickly.

Questions worth asking yourself:

• When I feel stalled, am I facing a real conflict between two things I care about, or a worry that has no concrete content?
• When I feel excited, would the plan still look good after a night’s sleep?
• Is this fear about something present, or about something that might happen?
• Which of my reactions has been helpful lately, and which has cost me?
• What small experiment could I run to test my prediction?

Imagine Naledi, 31, who has been offered a promotion that would mean managing her former peers. She’s flattered, and she dreads it. Using the theory as a prompt, she separates the two pulls: the approach side (status, income, learning) and the avoidance side (awkwardness, being disliked). Writing both lists reduces the fog. She asks her manager for a three-month trial, which lets her gather information instead of ruminating.

The same lens helps with other people. A partner who hesitates before every plan may not be dismissive; they may have a conflict system that needs time. A friend who says yes to everything may not be careless; their approach system may fire first and ask questions later. Seeing differences as differences in sensitivity, rather than in character, can soften arguments.

A caution: this isn’t therapy, and it doesn’t replace it. Persistent anxiety, panic, hopelessness, or impulsive behavior that causes harm deserves professional attention. If you’re struggling, a therapist, psychologist, or primary care doctor can offer evidence-based help such as cognitive behavioral therapy.

The theory’s best lesson is practical. Hesitation and boldness aren’t opposites on a scale of virtue. They’re two systems that, most of the time, work together to keep you both moving and alive.

FAQs about Jeffrey Gray’s Biological Theory of Personality

What is Gray’s reinforcement sensitivity theory in simple terms?

It’s a theory that personality differences come from how strongly three brain systems respond to rewards, threats, and conflicts. One system pushes you toward good things, one drives fear and escape from danger, and one detects conflict and makes you pause and worry. People differ in how sensitive each system is, and those differences show up as styles of behavior, such as boldness, caution, or restlessness. Jeffrey Gray developed the idea over several decades and revised it in 2000 with Neil McNaughton. It remains a theory under active debate rather than a settled fact.

What do BIS and BAS stand for?

BIS stands for behavioral inhibition system, and BAS stands for behavioral approach system, which is sometimes called the behavioral activation system. The BIS is linked with caution, conflict, and anxiety, while the BAS is linked with pursuing rewards. A third system, the fight-flight-freeze system, handles fear and escape in the revised theory. Many popular articles mention only BIS and BAS because the widely used questionnaire was built around those two. If you’ve seen the abbreviations on a personality blog, they almost always trace back to Carver and White’s 1994 questionnaire.

Is a high BIS score the same as having an anxiety disorder?

No. A high score on the BIS scale describes a tendency to be sensitive to punishment cues and to worry about mistakes. It correlates with anxiety symptoms in many studies, but plenty of people with high scores function well and never meet criteria for a disorder. Diagnosis depends on how much distress and impairment someone experiences, and it requires a clinical assessment by a qualified professional. A questionnaire result alone can’t tell you that. If worry is wearing you down, that’s reason enough to ask for an assessment, whatever any score says.

How is Gray’s theory different from the Big Five?

The Big Five describes personality using five broad traits identified largely through factor analysis of everyday language and questionnaires. Gray’s theory starts from motivation and neuroscience, asking which brain systems produce approach, avoidance, and conflict. The two overlap, since BAS relates to extraversion and BIS to neuroticism, but they differ in purpose. The Big Five is mostly descriptive, whereas RST tries to explain why certain patterns occur and makes predictions about learning and emotion. Some researchers have tried to map one onto the other, with partial success.

Can your BIS or BAS sensitivity change over time?

Probably to a degree, though research on long-term change in RST traits is limited. Temperament seems fairly stable across adulthood, but experience, stress, and treatment can shift how someone responds. Someone who learns to tolerate uncertainty may feel less trapped by worry even if their underlying sensitivity stays similar. It’s more accurate to say that behavior and habits change than to claim the brain systems themselves have been rewired. Anyone hoping to shift a pattern deliberately will usually get further by practicing new responses than by trying to change a trait.

Who was Jeffrey Gray?

Jeffrey Alan Gray was a British experimental psychologist and neuroscientist who worked at the University of Oxford and later at the Institute of Psychiatry in London. He is best known for his work on anxiety, the septo-hippocampal system, and the biological basis of personality, as well as for his later interest in consciousness. He died in 2004. His book The Neuropsychology of Anxiety is still cited widely, and its second edition with Neil McNaughton set out the revised version of the theory.

Why does the fight-flight-freeze system matter in the revised theory?

Because it separates fear from anxiety, which the original theory had blended together. Fear arises when a threat is present and calls for escape or defense, and the revised theory assigns it to the fight-flight-freeze system. Anxiety arises when danger is uncertain or conflicts with a goal, and belongs to the behavioral inhibition system. That split fits clinical observations better, since a panic response and chronic worry feel different and respond to different approaches, though the theory hasn’t yet been fully tested. It’s a useful idea, not a proven map.

Should I take an online BIS/BAS test?

You can, as long as you treat it as a thought exercise. The standard 20-item scale takes a few minutes and gives scores on inhibition, reward responsiveness, drive, and fun seeking. The results show how you describe yourself on a given day and say nothing about brain function or any disorder. If a result worries you, or if anxiety, low mood, or impulsive behavior is causing problems, it makes more sense to talk with a therapist or doctor than to keep taking tests. Consider it closer to a mirror than a measuring stick.

Bibliography

• Carver, C. S., & White, T. L. (1994). Behavioral inhibition, behavioral activation, and affective responses to impending reward and punishment: The BIS/BAS Scales. Journal of Personality and Social Psychology, 67(2), 319–333.
• Corr, P. J. (2004). Reinforcement sensitivity theory and personality. Neuroscience & Biobehavioral Reviews, 28(3), 317–332.
• Corr, P. J. (Ed.). (2008). The reinforcement sensitivity theory of personality. Cambridge University Press.
• Eysenck, H. J. (1967). The biological basis of personality. Charles C Thomas.
• Fowles, D. C. (1980). The three arousal model: Implications of Gray’s two-factor learning theory for heart rate, electrodermal activity, and psychopathy. Psychophysiology, 17(2), 87–104.
• Gray, J. A. (1970). The psychophysiological basis of introversion-extraversion. Behaviour Research and Therapy, 8(3), 249–266.
• Gray, J. A. (1982). The neuropsychology of anxiety: An enquiry into the functions of the septo-hippocampal system. Oxford University Press.
• Gray, J. A., & McNaughton, N. (2000). The neuropsychology of anxiety: An enquiry into the functions of the septo-hippocampal system (2nd ed.). Oxford University Press.
• McNaughton, N., & Corr, P. J. (2004). A two-dimensional neuropsychology of defense: Fear/anxiety and defensive distance. Neuroscience & Biobehavioral Reviews, 28(3), 285–305.