The transliminal brain at rest: Baseline EEG, unusual experiences, and access to unconscious mental activity

Abstract

Transliminality reflects individual differences in the threshold at which unconscious processes or external stimuli enter into consciousness. Individuals high in transliminality possess characteristics such as magical ideation, belief in the paranormal, and creative personality traits, and also report the occurrence of manic/mystic experiences. The goal of the present research was to determine if resting brain activity differs for individuals high versus low in transliminality. We compared baseline EEG recordings (eyes-closed) between individuals high versus low in transliminality, assessed using The Revised Transliminality Scale of Lange et al. (2000). Identifying reliable differences at rest between high- and low-transliminality individuals would support a predisposition for transliminality-related traits. Individuals high in transliminality exhibited lower alpha, beta, and gamma power than individuals low in transliminality over left posterior association cortex and lower high alpha, low beta, and gamma power over the right superior temporal region. In contrast, when compared to individuals low in transliminality, individuals high in transliminality exhibited greater gamma power over the frontal-midline region. These results are consistent with prior research reporting reductions in left temporal/parietal activity, as well as the desynchronization of right temporal activity in schizotypy and related schizophrenia spectrum disorders. Further, differences between high- and low-transliminality groups extend existing theories linking altered hemispheric asymmetries in brain activity to a predisposition toward schizophrenia, paranormal beliefs, and unusual experiences.

Introduction

The flow of information from unconscious to conscious awareness has been of great interest for centuries (e.g., Wallas, 1926). James (1890) suggested that thought was ongoing, switching intermittently between internal and external stimuli, relying heavily on processes needed to integrate the past with the present. More recently, researchers have examined the interface between unconscious and conscious processing in mental illness (e.g., Andreasen, 1997, Geyer et al., 2001), the role of the unconscious in the facilitation of problem solving and creativity (e.g., Bowden, 1997, Bowers et al., 1995, Carson et al., 2003, Jung-Beeman et al., 2004), and the nature of altered consciousness that accompanies paranormal beliefs and experiences (e.g., Thalbourne, 1994, Thalbourne and Delin, 1994).

Thalbourne and his collaborators have studied the transfer of unconscious thought and external stimulation into conscious awareness and have labeled individual differences in the degree of such transference as transliminality (Thalbourne and Houran, 2000). More specifically, transliminality has been defined as “susceptibility to, and awareness of, large volumes of imagery, ideation, and affect – these phenomena being generated by subliminal, supraliminal, and/or external input” (Thalbourne et al., 1997, p. 327). Individuals high in transliminality tend to believe in the paranormal, engage in magical ideation, have manic and/or mystical experiences, and possess creative personalities (Thalbourne and Delin, 1994).

Though the boundary between conscious and unconscious thought has been recognized as a source of individual differences in personality, cognition, and psychopathology, the link between transliminality and these psychological components has gone largely unexplored. A notable exception is the research of Crawley et al. (2002) which examined the relationship between transliminality level and performance on a subliminal card-naming task. When a masked prime of the ‘to-be-identified’ symbol was briefly displayed on the back of the card (<50 msec), participants high in transliminality were more accurate in identifying the target symbol on the reverse.

More is known, however, concerning the unique aspects of cognitive processing associated with transliminality-related traits such as positive schizotypy, out-of body experiences (OBEs), and belief in the paranormal (e.g., Bressan, 2002, Claridge, 1997, Tsakanikos and Reed, 2005). Schizotypal personality traits are muted levels of traits present in schizophrenia. These traits have been divided into positive (e.g., perceptual aberrations, hallucinations, and magical thinking), negative (e.g., physical and social anhedonia), and disorganized (e.g., irregular speech and thought) components (Vollema and Hoijtink, 2000, Vollema and Postma, 2002). Transliminality and positive schizotypy are positively correlated (Thalbourne, 1994, Thalbourne and French, 1995, Thalbourne et al., 2005), as are transliminality and disorganized cognition (Thalbourne et al. 2005), though to a lesser degree. Research has also supported a link between positive schizotypy and belief in the paranormal (e.g., Goulding, 2004, Goulding, 2005).

Those high in positive schizotypy and related traits exhibit altered cognition in perceptual, spatial, and linguistic domains, among others (e.g., McCreery and Claridge, 1996, McCreery and Claridge, 2002, van de Ven and Merckelbach, 2003). For example, individuals high in positive schizotypal traits were more likely to detect the presence of meaningful patterns (e.g., words) in visual displays where this information was absent (Tsakanikos and Reed, 2005; see also Fyfe et al., this issue). This pattern of results was also present in individuals expressing beliefs in the paranormal who were more likely than nonbelievers to detect meaningful patterns in random dot displays (Bressan, 2002, Brugger et al., 1993).

A growing body of research has revealed deviations from the normal patterns of hemispheric asymmetry accompanying cognitive processing in individuals high in transliminality and related personality components. For example, the typical left-hemispace bias in attention present in normal adults is enhanced in individuals high in positive schizotypal traits, exhibited in a further leftward shift in bias when performing the line bisection task (Mohr et al., 2003, Taylor et al., 2002) and related chimeric faces task (Luh and Gooding, 1999). This leftward shift in attention has been linked by researchers to hyperactivity in the right-hemisphere (Mohr et al., 2003; for an alternate view see Schulter and Papousek, this issue).

Crow (2000) has suggested that the breakdown in typical patterns of hemispheric organization, especially evident in the domain of language, is a key factor in the onset of schizophrenia. Enhanced indirect semantic priming has been demonstrated following the presentation of stimuli to the left visual field (right-hemisphere) in individuals high in positive schizotypal traits (e.g., Mohr et al., 2006) and in individuals reporting high levels of paranormal experiences and beliefs (Pizzagalli et al., 2001). Right-hemisphere hyperactivity in these groups may be linked to the dopamine hypothesis of schizophrenia, which suggests that positive schizophrenic traits are associated with hyperdopaminergia in right-hemisphere dopamine systems (e.g., Goldberg et al., 2000, Mohr et al., 2005).

Finally, unique lateralization patterns have been observed in the spatial characteristics of hallucinations occurring in conjunction with sleep paralysis and during OBEs (e.g., Brugger et al., 1996). Vestibular-motor hallucinations, such as floating and falling, comprise the types of experiences typical in OBEs (e.g., Cheyne and Girard, 2004, Girard and Cheyne, 2004). Girard and Cheyne observed a right-hemispace hallucination bias in right-handed individuals evident in rightward turning and movement. It has been suggested that vestibular-motor hallucinations are the byproduct of activation in the cortical vestibular system, a theory supported by the occurrence of OBEs and hallucinations following the subdural electrical stimulation in the region around the angular gyrus, the core of the vestibular system (Blanke et al., 2002).

Prior research has successfully demonstrated unique patterns of activity in resting electroencephalograms (EEGs) in relation to specific cognitive and affective traits, such as extraversion, schizophrenia, and working memory (e.g., Knyazev et al., 2003, Kumari et al., 2004, Winterer et al., 2001). For example, Winterer et al. observed hypoactivation in frontal and temporal regions of the brain stemming from increased slow-wave activity (i.e., delta) in patients with schizophrenia. In contrast, hyperactivation was observed in individuals with schizotypal personality disorder for comparable regions (Mientus et al., 2002, Wuebben and Winterer, 2001). Research has also suggested that resting brain activity may be predictive of the subsequent onset of psychosis (Manchanda et al., 2003).

Researchers have begun to examine patterns of brain activity associated with transliminality and related traits. Pizzagalli et al. (2000) examined differences in the resting EEGs of individuals high versus low in paranormal beliefs, exploring both the location and complexity patterns of cortical activity. Complexity patters are a reflection of the spatial distribution of total EEG power; lower complexity values reflect either a single distribution of activity with one underlying neural mechanism or the synchronized activity of multiple neural mechanisms (see Wackermann and Allefeld, 2007, for a review). In comparison to the asymmetry in hemispheric complexity present in normal adults (left > right), individuals high in paranormal beliefs exhibited a reduction in asymmetry linked to enhanced right-hemisphere and reduced left-hemisphere complexity patterns. Further, high beta activity (excitatory) was localized to the right-hemisphere in individuals high in paranormal beliefs, but to the left-hemisphere in nonbelievers.

Additional research has proposed the temporal lobes as the primary brain region involved in the determination of individual differences in transliminality level, though this theory has not been explored using neuroimaging or psychophysiological techniques. Thalbourne et al. (2003) have suggested that heightened levels of transliminality stem from increased connectivity in temporal regions. In their research, participants who exhibited high levels of transliminality also demonstrated enhanced temporal lobe lability, as indicated by scores on the Personal Philosophy Inventory (PPI; Persinger, 1984). The PPI assesses characteristics associated with temporal lobe functioning, such as epilepsy, odd sensory experiences, paranormal beliefs, and mania. Thalbourne et al.'s interconnectedness theory suggests that enhanced levels of temporal connectivity should be present with increasing transliminality.

Preliminary support for altered temporal lobe activity has been observed in individuals reporting near-death experiences (Britton and Bootzin, 2004). In their analysis of EEGs recorded during sleep for individuals reporting at least one prior near-death experience, Britton and Bootzin observed patterns of EEG activity associated with epileptic symptoms over the left temporal region. These individuals also scored significantly higher than normal adults on the temporal lobe symptoms of the PPI.

Understanding the brain activity accompanying altered consciousness (e.g., OBEs), as well as the activity influencing transliminality levels is a complex process mediated by a number of factors (e.g., sensory stimulation and baseline arousal levels; see Vaitl et al., 2005, for a review). The goal of the present research was to determine if resting brain activity could differentiate individuals high versus low in transliminality traits. Though one would expect differences between brain activity occurring in conjunction with normal thought and activity accompanying hallucinations and OBEs, reliable differences in resting brain activity when an individual is not engaged in directed cognition would support a predisposition for transliminality-related traits.

Prior research using self-report measures has linked transliminality components such as paranormal beliefs and unusual experiences with positive schizotypal traits (e.g., hallucinations and perceptual aberrations; Goulding, 2005). In line with prior research that observed differences in baseline brain activity between individuals high in paranormal beliefs and nonbelievers (Pizzagalli et al., 2000), we predicted that hemispheric differences in resting brain activity would exist between individuals high versus low in transliminality. Further, due to the link between transliminality and positive schizotypal traits, we expected that regions connected to processing differences in individuals high in schizotypal traits, such as the temporal lobes, would be regions where differences would exist between high- and low-transliminality participants.