Multichannel EEG of an advanced meditator was recorded during four different, repeated meditations. Locations of intracerebral source gravity centers as well as Low Resolution Electromagnetic Tomography (LORETA) functional images of the EEG ‘gamma’ (35–44 Hz) frequency band activity differed significantly between meditations. Thus, during volitionally self-initiated, altered states of consciousness that were associated with different subjective meditation states, different brain neuronal populations were active. The brain areas predominantly involved during the self-induced meditation states aiming at visualization (right posterior) and verbalization (left central) agreed with known brain functional neuroanatomy. The brain areas involved in the self-induced, meditational dissolution and reconstitution of the experience of the self (right fronto-temporal) are discussed in the context of neural substrates implicated in normal self-representation and reality testing, as well as in depersonalization disorders and detachment from self after brain lesions.
The search for the neural correlates of consciousness is experiencing an unprecedented interest in the scientific community (see Atkinson et al., 2000, for a recent review). This search aims at identifying neural processes that characterize distinct states of consciousness (e.g. dream, hypnosis, wakefulness) or specific contents of consciousness. The content or state of consciousness can be altered by numerous external factors, such as chemical agents (drugs), but also by various forms of external information input, e.g. hypnotic suggestions (Isotani et al., 2001). On the other hand, there are many reports on changes of the state of consciousness as experienced subjectively that were caused by purely internal factors (Pardo et al., 1993, Fink et al., 1999, Kimbrell et al., 1999 and Neuper et al., 1999). These changes reportedly can be achieved by self-induction, executing mental routines such as self-hypnosis, autogenic training or meditational exercises. The question arises whether these subjectively experienced differences are associated with measurable differences of brain activity.
A particular component of brain electric activity, the EEG ‘40-Hz’ or ‘gamma’ frequency band, was described as a prominent characteristic of brain electric activity during meditation (Banquet, 1973). The 40-Hz frequency band has also been hypothesized to play an important role in the brain mechanisms of normal, conscious experience (the ‘binding problem’) as well as of consciousness in general (Gray et al., 1989, Kulli and Koch, 1991 and Singer et al., 1997), after having been reported earlier in various orienting and problem-solving conditions in animal and man (Domino and Ueki, 1960, Bouyer et al., 1980 and Spydell and Sheer, 1982). Specifically, gamma band activity has been proposed to act as a mechanism for visual representation of objects and for binding distinct aspects of object perception into a coherent and unitary concept (for review, see Tallon-Baudry and Bertrand, 1999).
We utilized an opportunity to study the brain electric activity of an experienced meditator in order to test whether subjectively different meditations, i.e. different altered states of consciousness, are associated with the activity of different neuronal ensembles that work at the 40-Hz-frequency band. Two independent space-oriented approaches were employed for the analysis of the 27-channel brain electric data: source gravity center localization in the frequency domain (Lehmann and Michel, 1990) and cortical distribution of the generator activity [Low Resolution Electromagnetic Tomography (LORETA), Pascual-Marqui et al., 1994 and Pascual-Marqui et al., 1999]. The analyses yielded converging results, describing significantly different brain regions as active during the different meditations.
