The Psychophysiology of Personality Disorders
Angela Scarpa and Adrian Raine
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 1994), defines a personality disorder (PD) as 'an enduring pattern of inner experience and behavior that deviates markedly from the expectations of the individual's culture, is pervasive and inflexible, has an onset in adolescence or early adulthood, is stable over time, and leads to distress or impairment (p. 629)'. In general, PDs involve personality traits that have become severe and rigid enough to be dysfunctional or maladaptive, and are typically manifested in at least two of the following areas: cognition, affectivity, interpersonal functioning, or impulse control.
The DSM-IV distinguishes 10 specific PDs that are grouped into three broad clusters, based upon similarities in descriptive features. Cluster A includes the paranoid, schizoid, and schizotypal PDs, which describe individuals who often appear odd, eccentric, or suspicious. Cluster A PDs are also thought to be part of the schizophrenia-spectrum disorders due to their similarity in symptoms with schizophrenia, though milder in form. Cluster B includes the antisocial, borderline, histrionic, and narcissistic PDs, which describe individuals who appear dramatic, emotional, impulsive, or erratic. Finally, Cluster C includes the avoidant, dependent, and obsessive-compulsive PDs, which describe individuals who often appear anxious or fearful. Clusters B and C have been described as reflecting externalizing (i.e., dramatic, reactive, and aggressive) or internalizing (i.e., anxious, avoidant, and withdrawn) dimensions of personality, respectively, based upon their primary symptomatology (Scarpa et al., 1999).
Psychophysiology involves the study of cognitions, emotions, and behaviour as related to physiological principles and events (Cacioppo and Tassinary, 1990; see also Chapter IX in this volume). As such, psychophysiology can provide unique information on the cognitive, affective, interpersonal, and impulsive features of PDs that is relatively objective in nature. This chapter will describe psychophysiological studies of PDs, as grouped by cluster. Although such studies provide rich information on psychological processes related to PDs, relatively few PDs have been examined by psychophysiological techniques. Specifically, the schizotypal and antisocial PDs have been most abundantly studied in relation to psychophysiology; thus, this chapter must necessarily focus on these two. Whenever possible, this information will be supplemented with psychophysiological studies of the other PDs. Findings related to characteristics associated with the Cluster C PDs are also discussed.
As described above, Cluster A includes the paranoid, schizoid, and schizotypal PDs, which are thought to reflect psychosis-proneness or schizophrenia-spectrum disorder. In the DSM-IV, paranoid PD is defined as a pattern of suspiciousness whereby others' motives are interpreted as hostile or malevolent; schizoid PD is defined as a pattern of social detachment or indifference with a restricted range of affect; and schizotypal PD is defined as a pattern of cognitive and perceptual distortions, interpersonal deficits, and odd behaviour (American Psychiatric Association, 1994). Indeed, schizotypal and paranoid PDs are found with greater frequency in the relatives of probands with schizophrenia, although not all studies have been consistent (see Webb and Levinson, 1993 for a review).
Schizotypal PD, in particular, has been a focus of attention due to its symptoms seeming to reflect a milder form of those seen in schizophrenia. These include negative (or deficit) symptoms, such as social withdrawal or blunted affect, and positive (or excess) symptoms, such as perceptual aberrations or magical ideation. Social anhedonia (i.e., social indifference) and magical ideation seem most predictive of later psychosis (Chapman et al., 1995). As such, researchers have focused on comparing schizotypal PD to findings in schizophrenia, with the hope of discovering either a common genetic marker for vulnerability or a factor protective against the progression to full-blown schizophrenia. In this vein, the primary psychophysiological variables that have been studied in schizotypal PD are the skin conductance orienting response (SCOR), smooth pursuit eye movement (SPEM), and event-related potential (ERP), all of which have been found to be deviant in individuals with schizophrenia. Each of these variables and research on their relationship to schizotypal PD will be summarized in turn below.
and Schizotypal PD
Changes in the electrical activity of the skin generally occur in response to the presentation of novel stimuli in one's environment. For example, the presentation of a new tone generally causes an orienting response that is accompanied by increased electrical activity in the skin, and thus, a change in skin conductance levels called theSCOR. One useful model for understanding the SCOR has been that of template-matching (Ohman, 1979; 1985). In this model, novel stimuli are stored in short-term memory where they create neural 'templates'. Subsequent stimuli are matched against the template currently stored in short-term memory. If the two stimuli differ, preattentive mechanisms will fail to recognize the newly presented stimulus, thus requiring controlled processing of the new stimulus. However, if the stimuli match, habituation occurs. In addition to cases in which there is a mismatch between the 'stored' stimulus and the novel stimulus, controlled processing also occurs when the novel stimulus is recognized as significant, necessitating further processing. In either case, augmented controlled processing of information would produce a SCOR. Thus, the SCOR is a useful index of how one attends to and processes novel environmental stimuli (Dawson and Nuechterlein, 1984; Dawson et al., 1989).