Neurotransmitter Systems in the Personality Disorders
Matt Eks, Harold W. Koenigsberg and Larry J. Siever
According to DSM-IV (American Psychiatric Association, 1994), a personality disorder is 'an enduring pattern of inner experience and behaviour that deviates markedly from the expectations of the individual's culture'. This enduring pattern is 'inflexible and pervasive over a broad range of personal and social situations'. It 'leads to clinically significant distress or impairment in important areas of functioning'. The pattern is 'stable', 'of long duration' and 'its onset can be traced back to adolescence or early adulthood'.
Personality disorders represent a relatively new field of research within psychiatry, particularly with a neurobiological approach. People intuitively react and adapt differently to their surroundings. Hippocrates explained these differences in terms of the 'four humors', different combinations and balances of which led to different personality traits. Bumps on the head, shape of the skull, hair colour, and body stature are among other traits that have been studied in me search for biological correlates of personality. Biological factors, such as the ones mentioned above, and environmental factors, such as family environment, social class, or early life experiences, have been considered to be factors which contribute to 'create' our personalities. Psychoanalysts point to 'drives' and defence mechanisms to explain individual differences. Psychologists have defined psychometric dimensional factors in normal personality and proposed that their measures correlate with biological differences. Investigators are now focusing on finding these biological correlates in relation to different temperamental and character traits. This does not necessary imply that personality disorders are explainable by biology alone. A more likely perspective is that we inherit basic traits or endophenotypes that predispose to psychiatric disorders in interaction with the environment.
Clearly defined diagnostic criteria are an important prerequisite for studying the role of biology and environment in the personality disorders. To clearly demarcate them from the more symptomoriented psychiatric disorders, personality disorders were placed on Axis II in the DSM axial system. Personality disorders are categorized into three clusters: A, B, and C. Cluster A represents a group of personality disorders that are marked by isolation and eccentricity. Disorders in Cluster B are characterized by behaviours of acting out in a dramatic, emotional, and erratic way. Diagnoses in Cluster C include individuals who are anxious and fearful. It is important to emphasize that the DSM criteria are clinically derived schema for categorizing personality disorders. While we seek external validators for the diagnostic system, our knowledge of the biological correlates, pathophysiology, genetics, or aetiological factors has not yet progressed to the point that we can obtain biological validation of the personality disorder diagnoses. The DSM has, however, made it possible to diagnose personality disorders in a more uniform way and in that way identify more homogeneous patient populations for research studies. The advances in neuroscience and its adaptation to study the pathophysiology of the Axis I disorders also have benefited these research efforts. With the help of neuroimaging and neuroendocrine measurements, the mapping of the brain and the activity of its neurotransmitters is possible.
What makes this area interesting and difficult is the fact that what we are trying to study is the essence of what makes all of us who we are. What are the underlying reasons for the extreme problems some people have in relation to themselves and/or their surroundings? These are fundamental questions regarding personality and particularly personality disorders. As our knowledge about the central nervous system is increasing rapidly, evidence of correlations between personality traits and brain function is also increasing. We can see resemblances between Axis I disorders and personality disorders on Axis II, both in personality traits and in brain function (or dysfunction). We can see the therapeutic effects of medication on dysfunctional personality traits, but we still do not have a comprehensive knowledge of the exact mechanisms underlying personality and personality disorders.
Personality dysfunction may be conceptualized from either a categorical or a dimensional perspective. The categorical model defines a set of specific personality disorder diagnostic categories to which an individual belongs or does not belong. DSM-IV uses this approach with a polythetic system in which individuals may fit into a diagnostic category if they possess a subset of criteria characteristics from a larger set. Thus, individuals with differing clusters of symptoms may share the same diagnosis. In contrast to a categorical system, a dimensional approach identifies a set of features which vary in magnitude among individuals. Individual personality disorders are characterized by high levels of one or more of these dimensions. The temperamental traits that are critical in the different personality disorders show strong evidence of heritability (Torgersen, 1994). Patients rarely represent 'clear-cut' cases; they often demonstrate a mix of traits that do not fit under one single diagnosis. This makes it more fruitful to evaluate personality traits rather then specific disorders to identify such associations. However, the nature of the key traits or dimensions in personality and personality disorders and the specific neurotransmitters and brain systems that can be associated with these key dimensions have not been definitively established. While researchers do not fully agree on what dimensions are critical to the study of personality, there is a fair correspondence between different dimensional systems. Our knowledge of abnormalities in neurotransmitter function in psychiatric disorders such as depression, bipolar disorder, and anxiety has suggested avenues of approach in understanding the biology of the personality disorders (Ressler and Nemeroff, 2000).