The history of the schizoid personality begins in early descriptive psychiatry and continues through later temperament and constitutional theorists. Early writers emphasized different characteristics of the modern prototype. For example, Ribot (1890) invented the term anhedonia to describe the diminished ability to experience pleasure, characteristic of the schizoid pattern. Similarly, A. Hoch (1910) described what he called the shut-in personality, using adjectives such as reticent, seclusive, stubborn, and shy. Likewise, Kraepelin (1919, p. 213) spoke of an autistic personality existing in a healed and stable prepsychotic state, individuals who "narrow or reduce their external interests and contacts and [are notable for] their preoccupation with inward ruminations."
The term schizoid itself, however, can be traced to Bleuler (1922, 1929), who also gave schizophrenia its label in 1911. Schizoidness was seen by Bleuler as expressed to different degrees in everyone, achieving morbid intensity only in schizophrenia. More moderate schizoids were described as "shut in, suspicious, incapable of discussion, people who are comfortably dull" (1924, p. 441). According to Bleuler (1950, p. 40), "even in the less severe forms of the illness, indifference seems to be the external sign ... an indifference to everything—to friends and relations, to vocation or enjoyment, to duties or rights, to good fortune or to bad." The association between indifference and apathy and the schizoid personality has endured to the present. Leonard reflects both through his indifference to the criticism of his boss and lack of interest in social relationships or the surrounding world.
The essential distinction between the contemporary schizoid and avoidant personalities, outlined previously and recaptured theoretically by Millon (1969), was first put forward by Kretschmer (1925) under the labels anesthetic and hyperaesthetic. The hy-peraesthetic, or avoidant, was described using adjectives such as timid, shy, sensitive, nervous, and excitable. For Kretschmer, "their autism is a painful cramping of the self into itself. They seek as far as possible to avoid and deaden all stimulation from the outside" (p. 161). In contrast, the anesthetic, or schizoid, was described as flavorless and boring. Beneath their nondescript surface lay only "a nothing, a dark, hollow-eyed nothing . . . which twitches uncertainly with every expiring whim—nothing but broken pieces, black rubbish heaps, yawning emotional emptiness, or the cold breath of an arctic soullessness" (p. 150).
According to Kretschmer (1925), indifference was a cardinal trait engendered by lack of affective response: "He draws himself back into himself because he has no reason to do anything else, because all that is about him can offer him nothing" (p. 162). Such individuals were described as being without warmth and humor, but more important, they were regarded as being "affectively lame," that is, temperamentally and constitutionally disposed to lack an "adequate reaction to what we are doing and saying to him ... he can stand there with a puzzled face and hanging arms... in a situation that would electrify [anyone else]" (p. 170). For Kretschmer, then, schizoid characteristics could be traced to inborn biological deficiencies.
Although current theories are speculative, the role that biological factors play in the schizoid personality probably becomes stronger as the disorder becomes more extreme.
Focus on Physical Correlates
Body Weight and Personality Is Body Type Related to Personality?
A long tradition of clinical speculation compares body characteristics with psychopathol-ogy. Kretschmer (1925), for example, categorized individuals according to body build. The asthenic, one of four body types he proposed, was characterized by fragility, poor muscularity, and a frail bone structure. The greater an individual's resemblance to the asthenic prototype, according to Kretschmer, the greater the chance of developing schizophrenia.
Because body types are rather global variables, contemporary researchers have begun to focus on more specific measures. Low birthweight, for example, has been associated with the development of mental disorders later in life (Kopp & Kaler, 1989). Following up on this theme, Hebebrand et al. (1997) examined the relationship between the body mass index (an empirically derived statistic that correlates highly with body weight) and the schizoid personality and Asperger's disorder, a syndrome similar to autism, in a sample of male adolescents diagnosed with one of the two disorders. The body mass index of all patients was significantly below normal.
What mediates the relationship between body weight and the schizoid personality is unclear. Clinical records indicate abnormal eating behavior by some patients, including fussi-ness about food, preference for unusual foods, habits of eating alone or only when at home, and hypochondriacal fears related to food. One patient commented that he had always been a "poor eater" (Hebebrand et al., 1997). Many schizoids seem to withdraw not only from the social world but also from themselves; they may be relatively insensitive to feelings of hunger. However, schizoids also derive little pleasure from anything. Accordingly, they may simply be anhedonic for eating; they don't enjoy it, so they don't eat much.
Another area of research in psychopathology links exposure to traumatic environmental events to the development of later characteristics. Hoek et al. (1996) studied the relationship between schizoid personality and prenatal exposure to famine, created by the Nazi blockade of western Holland during the winter of 1944 to 1945. Their findings show that the children of pregnant women affected during the first trimester of gestation were at significantly greater risk of developing a schizoid personality. These results were similar to those obtained in a previous study (Susser et al., 1996) that looked at the relationship between prenatal exposure to famine and schizophrenia. Perhaps both disorders, then, can be seen as existing on a continuum of prenatal damage, though this is only speculation.
Because the capacity for a rich emotional life seems so fundamental to human nature, the notion that schizoids suffer some constitutional deficit of emotional capacity provides a simple and compelling explanation for other characteristics of the disorder. Although many introverts are relatively asocial, they nevertheless have numerous interests and a rich inner life. In contrast, extreme schizoids seem impervious to all emotion—even anger, depression, and anxiety—not just to joy and pleasure. Lacking a capacity to experience pleasure and pain, schizoids feel little reinforcement or punishment from the normal activities of human life. They fail to attach to caretakers, find later interpersonal relationships unrewarding, and develop few interests or hobbies, just like Leonard, the librarian. In fact, schizoids have no motivation to think about anything at all. Because emotion and motivation are usually seen as possessing a physical component, they seem chronically underreactive or underaroused, completely lacking energy and initiative. The biological perspective naturally goes far toward explaining the central characteristics of schizoids, at least in the DSM-IV version, which exists largely as a disorder built on the absence of normal capacities.
Nevertheless, the specifics of a biological explanation of the schizoid personality are lacking. Individuals closer to the threshold between normal introversion and the schizoid personality disorder, for example, may simply exist at the lower end of a genetically based distribution of emotional capacity, interpersonal sensitivity, physiological arousal, and perhaps even native curiosity. Tentative twin, adoption, and family pedigree studies suggest that schizoid personality disorder belongs with schizotypal personality disorder as part of a schizophrenic spectrum (Siever, 1992), though conclusive data are not yet available (Nigg & Goldsmith, 1994). In the most straightforward polygenetic model, schizophrenia would be expressed through the action of numerous genes. Schizotypal personalities would, therefore, receive either a smaller number of such genes or only some subset of defective genes. Schizoids would receive the fewest schizophrenic genes or some still more restricted subset. Perhaps normal introverts would receive one or two such genes. Alternatively, the expression of more insidious genes might be suppressed by the presence of other genes that compensate in some way. Any number of more complex possibilities might be imagined. Unfortunately, although twin, adoption, and family pedigree studies can establish a role for heredity, identifying the exact genes involved in carrying the expression of a disorder and their interaction is more difficult. Meehl (1962) developed a single dominant gene model, which connects the schizoid and schizotypal personalities with schizophrenia.
Although some genetic basis seems inevitable, other individuals with schizoid traits might suffer focal brain abnormalities, perhaps in the limbic system, which plays an important role in emotional reactions. Alternatively, some deficiency might exist in the reticular activating system, which provides constant excitement to cortical cells in the normal brain during wakefulness and REM sleep, thus accounting for the lack of alertness seen in many schizoids. Perhaps limbic or reticular cells are only thinly branched or defective in some other way. Alternatively, other mechanisms may be at work, with different abnormalities producing different variations within the basic schizoid pattern. Genetic explanations and research on brain structures are not necessarily mutually exclusive; perhaps the density of neural branching in the limbic area is itself under genetic control, for example.
Finally, a neurobiological scheme embracing many of the personality disorders has been put forward by Cloninger (1987b). Here, the adult expression of personality is seen as being strongly constrained by three broad biological temperaments, each of which is associated with a particular neurotransmitter. Schizoids are seen as being low in reward dependence, reflecting their social detachment or lack of interest in obtaining rewards from others; low in harm avoidance, reflecting their self-confidence; and low in novelty seeking, reflecting their behavioral rigidity. Contemporary accounts of the schizoid personality do not typically emphasize self-confidence, which is associated with the narcissistic personality. Instead, their aloof manner is not meant to imply arrogance, but instead refers only to their interpersonal distance. Because Cloninger's schizoid differs from the DSM conception, he suggests the term imperturbable schizoid be used to convey the more restricted neurobiological definition. We do not, for example, see a kind of encapsulated arrogance in the case of Leonard, the librarian.
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