Neuropsychology addresses the relationship of the brain to language, memory and perception. Some notable names in this field are Rene Descartes and Paul Broca. Rene Descartes (1596-1650) believed that behavior was caused by "animal spirits" that flowed through nerve tubes to various muscles in the body. Paul Broca (1824-1880) believed that different areas in the brain served various functions such as speech and memory. He discovered this by examining the brains of deceased individuals who had brain damage. Today, neuropsychologists use MRI, PET, and CAT scans of the brain to diagnose disorders and study various aspects of brain function.
There can be neuropsychological underpinnings to personality traits and personality disorders. For example, research has shown there is an association between pathological gambling and front-temporal lobe abnormalities. These abnormalities also correspond with personality traits like impulsivity and novelty seeking behavior. Another research example is that prefrontal cortex dysfunction is associated with traits and decision making in psychopathy.