A neuropsychologist is a psychologist who specializes in understanding the relationship between the physical brain and behavior. The brain is complex. Disorders within the brain and nervous system can alter behavior and cognitive function.According to the University of Rochester Medical Center, the role of a neuropsychologist is to understand how brain structures and systems relate to behavior and thinking. Neuropsychologists have a doctorate in psychology and training in neuropsychology. They often work in research or clinical settings.