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Personality neuroscience is a rapidly growing 
field that attempts to identify the neurobio -
logical underpinnings of psychological indi -
vidual differences (Allen & De  Young, 2017; 
De Young, 2010). Decades of research have 
shown that both nature and nurture, genetic 
and environmental forces, shape personality. 
Regardless of the exact proportion of distal 
causes that are genetic versus environmental, 
however, the proximal causes of personal -
ity are necessarily biological, located in the 
brain that generates behavior and experience. 
When the environment has a lasting effect on 
personality, it must do so by influencing the 
brain. Personality neuroscience is thus the 
approach by which we may come to under -
stand the physical mechanisms responsible 
for personality. We describe in this chapter 
the major methods of research in personality 
neuroscience, provide an overview of what 
has been learned so far, and offer some rec -
ommendations for researchers interested in 
pursuing research in this field.
Methods in  Personality  Neuroscience
Interest in the biological mechanisms of 
personality is long-  standing, dating back at 
least to ancient Rome and Galen’s humoral theory, in which personality characteristics 
were attributed to the preponderance of 
bodily substances such as phlegm and bile 
(Kagan, 1994). Effective scientific research 
on this topic, however, is relatively recent 
due to the need for technologies to measure 
the brain. Eysenck (1967) can reasonably be 
considered the father of modern personal -
ity neuroscience, developing theories of the 
neural basis of the personality traits extra -
version and neuroticism and publishing the 
first overview of the field, but even Eysenck 
was quite limited by the technologies of 
his time. He relied on relatively nonspecif -
ic biological constructs, such as “cortical 
arousal,” that could be measured by early 
electroencephalography (EEG) systems, and 
it was not until the emergence of functional 
magnetic resonance imaging (fMRI) in the 
1990s and its widespread adoption in the 
2000s that personality neuroscience began 
to generate a substantial body of evidence. 
Available technology is a crucial determi -
nant of science, and there are currently at 
least five important categories of biological 
assessment used in personality neuroscience.
1. Neuroimaging techniques . The most 
prominent of these is MRI, which creates 
images of the brain based on the magnetic CHAPTER 8
The Neurobiology of  Personality
Colin G. De  Young  
Rachael G. Grazioplene  
Timothy  A. Allen