The Biological Theory of Sensation Seeking Developed by Zuckerman

Marvin Zuckerman is one of the very few differential psychologists who have been able to develop a theory of a temperament dimension, one which skillfully combines the correlational with the experimental approach, studies on humans with research on animals, and behavior characteristics with biochemical and psy-chophysiological measures. This multidirectional approach made it possible for the author to develop a causal theory of individual differences in sensation seeking. In terms of the criteria presented in Table 3.1, the sensation seeking theory represents a monodimensional approach that developed in studies conducted on adults (and on animals). This theory has been presented by Zuckerman in scores of publications, some of which contain a general and comprehensive review (Zuck-erman, 1979, 1984c, 1994). Recently Zuckerman's research interests have been concentrated on the Big Five issue. Taking part in the discussion regarding the number and nature of basic personality factors Zuckerman (1992; Zuckerman, Kuhlman, Joireman, Teta, & Kraft, 1993) arrived at a solution that proposed the following five factors: impulsive sensation seeking, neuroticism-anxiety, aggression-hostility, activity, and sociability. Together with coworkers (Zuckerman, Kuhlman, Teta, Joireman, & Carroccia, 1992) he developed an inventory aimed at measuring these constructions. For reasons given in chapters 1 and 21 am not presenting Zuckeramn's contribution to the Big Five issue.

Theoretical Background

Zuckerman, working in the 1950s as a clinical psychologist, became sensitive to individual differences in human behavior. His clinical experience led him to construct an adjective checklist for measuring state and trait anxiety (Zuckerman, 1960).

In the initial stage of his research career Zuckerman (1969) was involved in studies on sensory deprivation. He paid attention to the fact that individuals behave differently under such circumstances. Some are resistant to sensory deprivation, while others react in a way that suggests that perceptual isolation is for them a stress situation (Zuckerman, 1964). To grasp the individual differences in the need for stimulation, Zuckerman, Kolin, Price, and Zoob (1964) developed a sensation seeking scale, the first of consecutive versions of this inventory constructed by Zuckerman.

The concept of optimal level of arousal, developed by Hebb (1955) from studies on sensory deprivation, became one of the crucial constructs that Zuckerman incorporated into his theory of sensation seeking. Of special importance for the application ofthe concept of arousal to the study of individual differences, and for a biological interpretation of the sensation-seeking trait, was Zuckerman's close contact with Eysenck and Gray. Eysenck's personality (temperament) theory, especially the biological basis of extraversion, as well as Gray's neuropsychological model of reward and punishment systems underlying individual differences in anxiety and im-pulsivity, were influential in molding Zuckerman's theory of sensation seeking.

The contemporary tendency to concentrate on neurotransmitters in the explanation of excitatory and inhibitory functions of brain activity present in Gray's theory, but also strongly advocated by others, especially in studies on reward pathways by Stein (1974, 1983), together with Zuckerman's educational background in biochemistry, contributed to the extension of the biological interpretation of the sensation seeking trait. Zuckerman devoted much attention to the biochemical correlates, especially to the brain monoamine systems, in determining individual differences in sensation seeking (Zuckerman, 1987a, 1994).

The Concept and Structure of Sensation Seeking

Zuckerman's research on sensation seeking from the beginning of the 1960s has undergone several changes. Zuckerman's interest in the sensation seeking phenomenon stems from studies on sensory deprivation conducted by the McGill School in the 1950-1960s (Hebb, 1955; Zubek, 1969) and by Zuckerman (1969) himself. Records taken during deprivation have shown that individuals behave, and react physiologically, in different ways to prolonged sensory deprivation. Taking into account this observation and the classic conceptualizations on motivation, such as instincts, drives, and needs (Hull, 1952; McDougall, 1923; G. Murphy, 1947), as well as a variety of arousal theories (e.g., Berlyne, 1960; Hebb, 1955; Fiske & Maddi, 1961 ; Leuba, 1955), Zuckerman introduced in the early 1960s the concept of sensation seeking understood as a "simple sensory need based on the optimal level of stimulation" (1979, pp. 98). Individual differences in the need for external stimulation permit predictions of stress reaction to sensory deprivation. Sensation seeking was considered by Zuckerman as a general factor, and the Sensation Seeking Scale-Form I was used for measuring this trait (Zuckerman et al., 1964).

An essential step in the construction of the sensation seeking theory consisted in formulating ten postulates (Zuckerman, 1969); the most important of these refers to individual differences. It states that, for such behaviors as cognitive and motor activity as well as for experiencing a positive emotional state there are individual specific optimal levels of stimulation and arousal. The optimal level of stimulation varies depending on such factors as age, learning experience, recent levels of stimulation, task demands, diurnal cycle, and, most important, the individual's constitutional characteristics. These characteristics, responsible for more or less stable individual differences in sensation seeking, comprise such components as reactivity of the CNS and ANS to specific classes of stimulation and strength of excitatory and inhibitory centers in the CNS.

Extensive psychometric studies conducted by Zuckerman in the 1970s led to the development of inventories for the assessment of the sensation seeking trait. But their main contribution was to the development of the sensation seeking construct. According to Zuckerman (1979): "Sensation seeking is a trait defined by the need for varied, novel, and complex sensations and experiences and the willingness to take physical and social risks for the sake of such experience" (p. 10). This definition, only slightly modified in recent publications (Zucker-man, 1994), emphasizes that it is not the physical value of stimuli that is the source of stimulation but their meaning, which varies depending on individual-specific experience.

It has also been shown that sensation seeking is not an undifferentiated, general factor, but has a structure composed of the following four subfactors: thrill and adventure seeking, experience seeking, disinhibition, and boredom susceptibility (see Zuckerman, 1979, 1984c, 1994).

Thrill and Adventure Seeking (TAS) is a trait that refers to the interest or desire to engage in outdoor, physical risk-taking activities and exciting sports, such as skiing, parachuting, and fast driving.

Experience Seeking (ES) is characterized by "seeking of arousal through the mind and senses through a nonconforming life-style" (Zuckerman, 1979, p. 102), such as unplanned traveling, associating with unusual types of persons, and an inclination to drug-taking.

Disinhibition (Dis), which has the strongest biological background, is a trait expressed in the tendency toward seeking release and social disinhibition through drinking, sex, gambling, partying, and so forth. It applies to activities performed in the hedonistic pursuit of pleasure.

Boredom Susceptibility (BS) reflects aversion for repetitive experience, routine work, and boring people, and is expressed in restlessness in an invariable environment.

Zuckerman's view on the nature and structure of the sensation seeking construct has remained constant. What has changed over his many years of study is the biological interpretation of the sensation seeking trait.

The Biology of Sensation Seeking

Under the influence of Eysenck's biological interpretation of extraversion, Zuckerman (1974; Zuckerman, Murtaugh, & Siegel, 1974) formulated a hypothesis according to which the cortico-reticular feedback arousal system is responsible for individual differences in sensation seeking. Individuals differ in the need for optimal stimulation. Sensation seekers need high stimulation for maintaining the optimal level of arousal whereas sensation avoiders need low stimulation for maintaining the same level of arousal.

Standard measures accepted as indices of arousal, such as amplitude (intensity) characteristics and orienting reflexes (ORs) expressed in electrodermal and cardiovascular activity as well as the augmenting-reducing phenomenon in the domain of evoked potentials (EPs)2 were used by Zuckerman (1979, 1983a, 1984b, 1984c, 1990; Zuckerman, Buchsbaum, & Murphy, 1980) as basic markers of the sensation seeking trait.

According to Zuckerman, data seem to support the hypothesis that high sensation seekers characterized by a need for novel sensations have a stronger OR as compared with low sensation seekers. Experiments in which EP amplitudes were used as physiological correlates of sensation seeking refer to the relationship between the level of cortical arousal and the intensity of stimulation. These studies

2Studies on electrodermal and cardiovascular activity and EP measures related to temperament, including the sensation seeking dimension, are presented in detail in Chapter 4.

have mostly shown that, in high sensation seekers, increases in intensity of stimuli go together with increases of EP amplitude (augmenting phenomenon). In low sensation seekers the opposite phenomenon occurs: increases in stimulus intensity, particularly at high intensities, cause a decrease in EP amplitudes, a reducing phenomenon explained by the Pavlovian construct of protective inhibition (see Chapter1).

Under the influence of his own findings as well as of those reported in the literature regarding the biochemical correlates of sensation seeking behavior in man and animals, Zuckerman (1991 a, 1991c) modified his view on the biological bases of the sensation seeking trait. An experiment conducted by Carrol, Zuckerman, and Vogel (1982) showed that high and low sensation seekers did not report different feelings and did not show differences in behavioral efficiency in performance tests under depressant (diazepam) and stimulant (D-amphetamine) drugs, as predicted by the optimal level of arousal theory. Both high and low sensation seekers reported positive feelings and functioned best after administration of amphetamine, that is, with a higher level of arousal.

Many studies, mainly on animals, have shown the importance of the limbic system and the monoamine neurotransmitters3 which mediate the reward mechanism underlying the approach behaviors that can be identified as sensation seeking (Gray, 1973; Olds & Olds, 1965; Schneirla, 1965; Stein, 1974, 1983). Influenced by these studies, Zuckerman (1979) put forward the following hypothesis:

Sensation-seeking trait is in some part a function of the levels of the catecholamines norepinephrine and dopamine in the reward areas of the limbic system, as well as the neuroregulators that control their availability at the synapses within these neural systems. (p. 372)

Studies by Zuckerman and others (see Chapter 4) in which platelet MAO activity was related to sensation seeking have shown that, in general, sensation seeking is negatively correlated with platelet MAO activity. The relationship between MAO activity and sensation seeking is explained by the fact that limbic DA sensitizes exploratory tendencies and behavioral activity. High levels of MAO activity serve the function of degrading dopamine, thus decreasing the sensation seeking tendency (Zuckerman, 1983a, 1983b, 1984c, 1994).

Psychometric studies on sensation seeking have shown that this temperament trait is higher in males than in females, and decreases with age. This suggested that sensation seeking is related to gonadal hormones. Studies by Daitzman and Zuck-erman (1980, see also Zuckerman, 1984c, 1991c) pointed out that individuals who score high on the Disinhibition scale (high disinhibitors) are higher than low disinhibitors on testosterone, estrone and estriadol. Thus, besides physiological and

3The biochemical correlates of temperament, especially the monoaminergic neurotransmitters, seroto-nine, norepinephrine (NE), and dopamine (DA) and the enzyme that inactivates these neurotransmitters—monoamine oxidase (MAO—are discussed in detail in Chapter 4.

neurochemical correlates, hormonal markers of the sensation seeking traits were also found by Zuckerman and his coworkers.

Since sensation seeking has an evident biological basis, it is logical to expect that the biological endowment has a genetic origin. If so, heredity plays an important role in determining individual differences in sensation seeking. Only a few behavior-genetic studies have been hitherto conducted. Some of them have shown that heritability of the sensation seeking trait is about h2 = .60 (H. J. Eysenck, 1983a; Fulker, Eysenck, & Zuckerman, 1980; Koopmans, Boomsma, Heath, & van Dornen, 1995) which is one of the highest scores among temperament dimensions. As reported by Zuckerman (personal communication, June 1994) an unpublished study by Lykken and coworkers shows the same results for twins separated during their formative years and raised in different families.

To summarize, the range of physiological and biochemical correlates of sensation seeking is very broad. If we add the studies regarding heritability of this temperament trait, it follows that the biological model for sensation seeking, merely outlined here, is a highly complex one, as illustrated in Figure 3.5.

The Psychometric Measures of Sensation Seeking

As already mentioned, the first attempt to measure individual differences in the sensation-seeking tendency was made by Zuckerman in studies on deprivation,

FIGURE 3.5. A biological model for sensation seeking. Note. From Behavioral Expressions and Biosocial Bases of Sensation Seeking (p. 24), by M. Zuckerman, 1994, New York: Cambridge University Press. Copyright 1994 by Cambridge University Press. Reprinted with permission.

which resulted in the development of the first form of the Sensation Seeking Scale (SSS-Form I; Zuckerman et al., 1964). This 50-item scale was expected to measure sensation seeking as a general factor, understood as a simple sensory need based on the optimal level of stimulation (Zuckerman, 1979, p. 98). Since then, the Sensation Seeking Scale has undergone several changes and, altogether, six forms have been developed by Zuckerman.

Form II of the Sensation Seeking Scale consisted of a reduced number of items (34), of which 22 composed the General sensation seeking scale and 12 referred to gender-specific behavior characteristics.

Taking as a starting point 50 items from the SSS-Form I and 63 new items, Zuckerman (1971) constructed the SSS-Form III which made it possible to grasp the specific components of the sensation seeking trait. Factor analysis of the items resulted in the construction of scales which remained in the two consecutive forms of the SSSs—Thrill and Adventure Seeking, Experience Seeking, Disinhibition, and Boredom Susceptibility, the last scale more typical for men than for women. The factor structure which consists of the four sensation seeking traits has been replicated in many countries (Zuckerman, 1994).

Forms IV and V of the SSS gained their greatest popularity among sensation seeking researchers. SSS-Form IV consists of 72 items. It includes the General scale from Form II and four factor scales which developed from work with the SSS-Form III On the basis of an extensive investigation conducted on American and English male and female samples, the number of items for each of the four scales—TAS, ES, Dis, and BS, was reduced to 10, resulting in a 40-item questionnaire known as the SSS-FormV (Zuckerman, Eysenck, & Eysenck, 1978). As distinct from SSS-Form IV, Form V does not have a separate sensation seeking general scale. Sensation seeking as a general factor (tendency) may be measured by taking into account the total score from the four subscale scores (from all 40 items).

For all five forms of the SSS, forced-choice items were constructed so that one item represents one pole of the sensation seeking tendency and the other the opposite pole, as for example:

A: I have tried marijuana or would like to (+ES). B: I would never smoke marijuana (-ES).

Zuckerman (1979) presents the details regarding the psychometric characteristics of the Sensation Seeking Scales Forms IV and V Alpha Cronbach correlations for the TAS scale vary between .77 and .88 and for ES and Dis between .61 and .85. Unsatisfactory reliability scores, ranging from .38 to .66, were obtained for the Boredom Susceptibility scale.

In the 1980s, Zuckerman (1984a) developed the SSS Form VI, but it did not gain much popularity, This scale is constructed around the distinction between sensation seeking items which refer, on the one hand, to past experiences of the reporting person, and, on the other, to desired or intended future experiences. Since the TAS scale and the Dis scale are more orthogonal to each other than the remaining scales, the SSS-Form VI refers only to these two subtraits. In consequence, Zuckerman developed the following four scales: Experience-TAS, Intention-TAS, Experience-Dis, and Intention-Dis. The SSS-VI comprises 128 items with three response options for each item.

The Behavioral Correlates of the Sensation Seeking Trait

Several studies have been carried out in which sensation seeking, as measured by means of the SSSs (Forms IV and V), was related to different risk-taking activities and to behavior in situations differing in stimulative value. Further, the relationship between sensation seeking and different kinds of behavior disorders (e.g., drug use, delinquency, criminal behavior, pathology) was frequently investigated. The results reported by Zuckerman and his coworkers, as well as by researchers from other laboratories, have been summarized by Zuckerman in several monographs (1979, 1984c, 1994).

As suggested by the definition of sensation seeking, the majority of findings support the assumption that sensation seekers prefer activities and situations that are novel, rich in stimulation, or both, which require risky behavior or which satisfy hedonistic needs, regardless of whether these activities are socially accepted or whether they represent normal or abnormal behavior, including pathology. For example, there is evidence that among sensation seekers there are significantly more alcoholics, drug abusers, criminals, psychopaths, and delinquents than among sensation avoiders (Zuckerman, 1979, 1984c, 1987b, 1994). After two decades ofre-search on the nature of sensation seeking Zuckerman (1994) concluded that

[t]he only thing constant in the life of high sensation seekers is change. They change activities, sexual and marital partners, and drugs, just as they switch from one channel to another if compelled to watch television for any length of time. (p. 374)

The need for change seems to be the most typical behavior characteristic for a sensation seeker.

To explain the relationship between the sensation seeking trait and behavioral expressions of sensation seeking, Zuckerman refers to the concept of optimal level of arousal. In contrast to his former view adapted from H. J. Eysenck (1967) according to which the cortico-reticular loop was responsible for regulating the level of arousal, Zuckerman developed a biochemical theory of arousal. This theory is based on the concept of optimal level of the catecholamine systems activity (Zuckerman, 1984c, 1987a, 1994). The catecholamines, dopamine and norepinephrine, are regarded as activating systems (see Chapter 4).

The general term catecholamine systems activity (CSA) is used to summarize the net effect of production, rate of release, metabolism, disposal, and receipt sensitivity on the general level of activity in these systems. . . . Adaptability in general is postulated to be a function of CSA activity, neuroregulators such as MAO, and neurotransmitters such as serotonin and endorphins that generally seem to regulate actions of the catecholamines. There is a tonic level of CSA . . . that is adap-tively optimal [emphasis added] for mood (positive hedonic tone), general activity, and social interaction. (Zuckerman, 1984c, p. 431)

As illustrated in Figure 3.6, there is an inverted U relationship between adaptability and the activity of the catecholamine system. From the point of view of adaptation, expressed by mood, activity, social interaction, and clinical condition, an average level of CSA (point C in Fig. 3.6) is optimal. At both extremes of CSA levels (points A and E, F) a low level of adaptability occurs, which is expressed by behavior disorders and negative mood, such as anxiety or panic.

The sensation seeking tendency, expressed in the need for intense and novel stimuli, in engagement in risky and fear-provoking activities, and in inclination to drugs, may be explained by the chronically low level of CSA typical for high sensation seekers who tend to search for stimuli and to perform activities that increase the tonic level of CSA. The opposite tendency occurs in sensation avoiders who, because of their chronically high level of CSA, tend to behave in a way that leads to a decrease of the tonic level of CSA.

Final Remarks

Among contemporary temperament theories the sensation seeking conceptualization belongs to those with well-established traditions. The intensive and extensive studies of Zuckerman and his coworkers over two decades have yielded a large amount of evidence in favor of his ideas and hypotheses. His theory, which exemplifies a complex and interdisciplinary approach to the sensation seeking ten-

FIGURE 3.6. A model for the relationships of mood, activity, social interaction, and clinical conditions to catecholamine system activity (CSA). Note. From "Sensation Seeking: A Comparative Approach to a Human Trait," by M. Zuckerman, 1984, Behavioral and Brain Sciences, 7, p. 431. Copyright 1984 by Cambridge University Press. Reprinted with permission.

FIGURE 3.6. A model for the relationships of mood, activity, social interaction, and clinical conditions to catecholamine system activity (CSA). Note. From "Sensation Seeking: A Comparative Approach to a Human Trait," by M. Zuckerman, 1984, Behavioral and Brain Sciences, 7, p. 431. Copyright 1984 by Cambridge University Press. Reprinted with permission.

dency, has gained considerable popularity among differential psychologists. The data collected by Zuckerman and others, however, include some results that are not compatible with the expectations postulated by the theory. Furthermore, the theory is ambitious and has some shortcomings. The most extensive critique of Zucker-man's sensation seeking approach was presented in his target article: "Sensation Seeking: A Comparative Approach to a Human Trait" (Zuckerman, 1984c). I refer first to those comments on which some reviewers agree.

Zuckerman's sensation seeking model does not offer a specific sensation seeking profile of physiological and biochemical markers. These biological correlates may also be found for such traits as extraversion or impulsivity (Barratt; Neufeld; Panksepp, & Siviy; Stelmack—in Zuckerman, 1984c).

The global treatment of catecholamines, as expressed in the CSA concept, does not have empirical support. Data regarding the relationship catecholamines-sensa-tion seeking are contradictory. Further, neurotransmitters, depending on their location and concentration, and on the interaction with other neurotransmitters and hormones, have a variety of different functions unaccounted for by Zuckerman's CSA construct (Von Knorring; Mason; Redmond—in Zuckerman, 1984c).

The sensation seeking model underestimates the role of environment, especially the social context, in determining the specific aspects of sensation seeking as expressed in the four sensation seeking traits—TAS, ES, Dis, and BS. For these components of sensation seeking as well, no specific physiological or biochemical markers have been postulated by Zuckerman (Baldwin; Strelau—in Zuckerman, 1984c).

Questions passed over by the reviewers of the target article refer to the sensation seeking scales and to the population on which these scales have been used. A careful reader of Zuckerman's publications will easily conclude that most of his work has been conducted on students. His findings have therefore a kind of academic bias, and may not apply to populations that extend beyond the university sphere. It must be added, however, that data collected by others on nonstudent populations are consistent with Zuckerman's (1994) findings.

Among the many personality and temperament questionnaires known to me, the sensation seeking scales are the most culturally biased. Many items refer to behaviors (e.g., I have tried marijuana), situations (e.g., "wild" uninhibited parties), attitudes (e.g., I dislike "swingers"), and activities (e.g., parachute jumping) unknown or rarely met in other cultures, and even when known, hardly ever experienced by the subjects under study. These features ofthe SS scales render it difficult to adapt the SS inventories to other countries or languages (see Andresen, 1986; Oleszkiewicz, 1982).

Over the past few years much of Zuckerman's research has been devoted to the structure of so-called basic personality dimensions (see Chapter 1). Among these, a particular kind of sensation seeking — Impulsive Unsocialized Sensation Seeking (P-ImpUSS)—constitutes one of the five postulated factors (Zuckerman, 1993; Zuckerman, Kuhlman, Thornquist, & Kiers, 1991). Logically and linguisti cally the phrase "impulsive unsocialized sensation seeking" suggests that this general factor covers only a part of the sensation seeking trait, and thus should be regarded as an additional component ofTAS, ES, Dis, and BS. This, however, is contrary to Zuckerman's view according to which the abbreviation P-ImpUSS means a factor composed of impulsivity, socialization, and sensation seeking with "psychopathy" as the extreme, clinical, manifestation.

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