So far we have discussed several theories of personality. These theories emphasize the importance of the psychological and social aspects of the bio-psycho-social model. It remains for us to discuss neurobehavioral theories of behavior. These theories emphasize the biological portion of the bio-psycho-social model. These neurobehavioral theories are not limited to theories of personality per se. Rather they are theories that more broadly account for human behavior in biological terms.
Neurobehavioral studies examine the biological underpinnings of our experience and behavior. This focus includes investigations of how the brain functions to influence our thoughts, emotions, and interactions with the world. As a result of this research, we now have a much greater our understanding of how the brain is constructed. This enables us to better understand how it processes and stores information. It also clarifies the various functions served by the many different brain regions, structures, and chemicals.
Rapid technological advancement, particularly within the field of neuroimaging, has allowed us to study the brain as never before. These new imaging technologies have enabled researchers to study brain regions and structures that are believed to influence our subjective interpretations. These interpretations of our environment influence our emotions, and our ability to regulate our emotions. These are all functions central to any understanding of personality and personality disorders.
In their review of neurobiological research, Coccaro and Siever (2005) reported that people with Schizotypal Personality Disorder have some of the same brain abnormalities found in people with diagnoses of Schizophrenia. These similarities include brain chemicals and structures known to be critically important for the proper functioning of affect, (emotion) perception, attention, and certain types of memory. These are the very symptoms that affect both disorders. This finding informs our understanding of the biological bases of psychotic-like symptoms. This helps us to understand why Schizotypal Personality Disorder occurs more frequently in relatives of people who have Schizophrenia than in the general population (Coccaro & Siever, 2005). Interestingly, people with Schizotypal Personality Disorder appear to be able to compensate for some of these difficulties by relying on other (undamaged) brain functions. This ability may account for the reason that the Schizotypal Disorder is not quite as debilitating as Schizophrenia.
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Similarly, abnormal brain chemistry profiles are frequently implicated in certain types of personality disorders. Coccaro and Siever (2005) reported that researchers have identified a relationship between impulsive aggression and a complex neuro-chemical system called the serotonergic system. This finding suggests there is biological, neurological etiology for the symptom of impulsive aggression that is characteristic of Cluster B personality disorders (Antisocial, Borderline, Histrionic, Narcissistic).
Cluster B personality disorders are also characterized by emotional dys-regulation. Coccaro and Siever (2005) also reviewed brain imaging studies that found people with Cluster B personality disorders, had reductions in the volume of certain brain regions associated with the regulation of emotions. Once again, this finding offers compelling evidence for a biological explanation for the symptom of emotional dys-regulation. While there is less research available for Cluster C personality disorders (Avoidant, Dependent, Obsessive-Compulsive), there are some indications that neurotransmitters, such as dopamine and serotonin, likely play an important role in these disorders as well (Coccaro & Siever, 2005).