The biological basis of personality it is the collection of brain systems and mechanisms that underlie human personality. Human neurobiology, especially as it relates to complex traits and behaviors, is not well understood, but research into the neuroanatomical and functional underpinnings of personality are an active field of research. Animal models of behavior, molecular biology, and brain imaging techniques have provided some insight into human personality, especially trait theories.
Much of the current understanding of personality from a neurobiological perspective places an emphasis on the biochemistry of the behavioral systems of reward, motivation, and punishment. This has led to a few biologically based personality theories such as Eysenck’s three factor model of personality, Grey’s reinforcement sensitivity theory (RST), and Cloninger’s model of personality. The Big Five model of personality is not biologically based; yet some research in the differences in brain structures provided biological support also for this model.
Personality can be defined as a set of characteristics or traits that drive individual differences in human behavior. From a biological perspective, these traits can be traced back to brain structures and neural mechanisms. However, this definition and theory of biological basis is not universally accepted. There are many conflicting theories of personality in the fields of psychology, psychiatry, philosophy, and neuroscience. A few examples of this are the nature vs. nurture debate and how the idea of a ‘soul’ fits into biological theories of personality.
Since the time of the ancient Greeks, humankind has attempted to explain personality through spiritual beliefs, philosophy, and psychology. Historically, studies of personality have traditionally come from the social sciences and humanities, but in the past two decades neuroscience has begun to be more influential in the understanding of human personality.
However, the most cited and influential figures in publishing the first biology-based personality theories are Hans Eysenck and Jeffrey Alan Gray. Eysenck used both behavioral and psychophysiological methodologies to test and develop his theories. He published a book in 1947 called Dimensions of Personality, describing the personality dimensions of extraversion and neuroticism. Gray, a student of Eysenck, studied personality traits as individual differences in sensitivity to rewarding and punishing stimuli. The significance of Gray’s work and theories was his use of biology to define behavior, which stimulated a lot of subsequent research.
In 1951, Hans Eysenck and Donald Prell published an experiment in which identical (monozygotic) and fraternal (dizygotic) twins, ages 11 and 12, were tested for neuroticism. It is described in detail in an article published in the Journal of Mental Science in which Eysenck and Prell concluded that “The factor of neuroticism is not a statistical artifact, but constitutes a biological unit which is inherited as a whole … neurotic predisposition is to a large extent hereditarily determined.” The study concluded that the neuroticism trait was a result of up to eighty percent of genetics. There was a stronger correlation among identical twins rather than fraternal twins .
The idea of biology-based personality research is relatively new, but growing in interest and number of publications. In August 2004, there was a conference specifically on the topic, called The Biological Basis of Personality and Individual Differences. This allowed for presenting and sharing of ideas between psychologists, psychiatrists, molecular geneticists, and neuroscientists, and eventually gave birth to the book under the same title.
The book is a collection of current research (as of 2006) in the field contributed by many authors and edited by Turhan Canli. Recently, psychology professor Colin G. DeYoung has even named the idea as the field of “Personality Neuroscience.” Furthermore, a journal devoted to cultivating research investigating the neurobiological basis of personality has recently been established and is called “Personality Neuroscience.”