Verbal creativity and schizotypal personality in relation to prefrontal hemispheric laterality: A behavioral and near-infrared optical imaging study
Introduction
Archival and biographic data from individuals with psychotic illnesses and from their relatives have supported the association between creativity and mental illness; however, few studies have used hypothesis-driven and empirical methods to examine the link between creativity and psychosis.
There is overwhelming support for a positive relationship between creativity and schizotypy (cf. Eysenck and Furnham, 1993, Gianotti et al., 2001, Kline and Cooper, 1986, Merten and Fischer, 1999, O'Reilly et al., 2001, Poreh et al., 1994, Rawlings and Toogood, 1997, Rushton, 1990, Rust et al., 1989, Weinstein and Graves, 2001, Weinstein and Graves, 2002, Woody and Claridge, 1977, Zanes et al., 1998) but currently, there is little support for enhanced creative ability in schizophrenics (Andreasen and Powers, 1975, Cropley and Sikand, 1973, Keefe and Magaro, 1980, Shimkunas and Murray, 1974). Yet, several studies using retrospective analyses of birth records, found support for increased creativity in the relatives of schizophrenic individuals, rather than in the probands themselves (Karlsson, 1970, Karlsson, 1984). These results suggest that enhanced creativity may be masked by the psychotic illness in the probands but can be detected in those individuals who share a latent liability for psychosis. Examining a clearly defined aspect of creativity in relation to brain laterality in schizotypal individuals or those at high risk for schizophrenia is warranted.
Two major established theories define the process and products of creative thinking. Guilford (1959) has emphasized divergent thinking (DT) and the use of generative, flexible responses that redefine or elaborate upon an existing product or idea. Mednick (1962) built upon this definition, showing that creative thinking emphasizes generating novel associations. DT has emerged as a valid core element in the creative thinking process (Bartlett and Davis, 1974, Torrance, 1988).
The spread of activation through semantic networks is central to verbal DT models. When indirectly related associations are activated, creative solutions are thought to be enhanced (Mohr et al., 2001, Pizzagalli et al., 2001). Schizophrenic patients (Spitzer et al., 1993, Weisbrod et al., 1998) and schizotypes (Gianotti et al., 2001, Mohr et al., 2001, Pizzagalli et al., 2001) show increased indirect semantic priming, suggesting that semantic organization may be altered and accessing indirect connections may be easier for psychosis-prone individuals. It is also possible that greater spreading activation could increase across hemispheres in individuals who have decreased cerebral lateralization. The right frontal lobe is involved in generating unusual or distant verbal associations while the left frontal lobe is involved in generating “usual” associations (Kiefer et al., 1998, Seger et al., 2000) Enhanced creativity and schizotypy may be associated with increased interhemispheric transfer (Miran and Miran, 1984), thereby making more efficient use of bilateral networks to generate associations.
Increased hemispheric interactions and reduced laterality may be central to both schizophrenia and creativity. Divergent and creative thinking may be characterized by increased cooperation of the two hemispheres (Atchley et al., 1999, Bekhtereva et al., 2000, Carlsson et al., 2000), and reduced hemispheric dominance has been linked to creativity (Claridge and Broks, 1984). Schizophrenia is associated with reduced functional and structural laterality. There is robust support for mixed handedness in schizophrenia (Cannon et al., 1995, Crow et al., 1996, DeLisi et al., 2002) and in schizotypes (Chapman and Chapman, 1987, Claridge et al., 1998, Kim et al., 1992, Richardson, 1994) rather than pure left-handedness (Shaw et al., 2001). Mixed handedness is associated with decreased cerebral lateralization, schizotypy, and enhanced creativity (Claridge and Broks, 1984). However, several neuroimaging and lesion studies also report specific RH correlates of creative thinking (Bowden and Beeman, 2003, Jung-Beeman et al., 2004, Martindale et al., 1984, Miller and Tippett, 1996, Razumnikova, 2004), although such unilateral functional preference may also be an outcome of intrahemispheric cooperation (Petsche, 1996, Razoumnikova, 2000). However, a direct comparison of these studies is problematic because definitions of “creativity” vary wildly.
In the present study we examined creative performance in normal controls, schizophrenics, and psychometrically ascertained schizotypes using a novel DT task in order to: (1) test the association between enhanced creativity and schizotypy; and (2) elucidate the neural correlates of DT. We examined hemispheric prefrontal activation during creative thinking using near infrared spectroscopy (NIRS) in a subset of subjects from the behavioral experiment. We hypothesized that DT would be associated with greater bilateral PFC activity and that the schizotypes would show greater PFC activity during DT than other groups.
Section snippets
Subjects
Demographic information is presented in Table 1. 17 outpatient schizophrenic (SZ) subjects who met the DSM-IV criteria were recruited from a local clinic. 17 healthy control (CO) and 17 schizotypal (SCT) subjects were recruited from the community. Exclusion criteria included substance abuse, neurological disorders, and history of head trauma. All patients were taking atypical antipsychotic drugs and were clinically stable. There were no significant group differences in education, handedness, or
Results
RAT: For the number of correct responses on the RAT, there was a main effect of group (F(2, 48) = 4.03, p < 0.05; r = 0.39). Normal controls (M = 10.0, SD = 6.1) gave more correct responses than schizophrenics (M = 5.5, SD = 4.3) (p < 0.05).
DTT: We recorded the number of singular and combinatory uses. For each trial, single object “use” responses were summed. Combinatory responses were calculated for each trial by summing the number of responses that included a use for at least two objects within the stimulus
Discussion
The major findings of this study were that: (1) schizotypy is associated with enhanced DT; (2) DT is particularly associated with disorganized schizotypal traits; (3) DT is associated with bilateral PFC activity; and (4) Schizotypes, who have enhanced creative thinking ability, recruit the right PFC preferentially compared to SZ and CO.
To our knowledge, this is the first study to compare the functional neuroanatomy of DT in SCT, SZ and CO. Our data support evidence for enhanced DT in
Acknowledgments
We thank Crystal Gibson, Chris Cannistraci, Susan J. Hespos, John Gore, Gordon Claridge, Peter Brugger, Christine Mohr, and Lynn DeLisi. This work was supported in part by the Discovery Grant to S.P. and by an NIMH training grant (T32-MH18921) and NICHD Grant P30HD15052.
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