**2.3 OVO Whole-Body Perceptual Deprivation (OVO-WBPD)**

As we will see in the current section, studies examining perceptual movement, where movement is absent and stillness is the main feature, were also found to be related mostly on delta waves. While delta has historically been associated with sleep and pathological processes, it has recently been found to be related to both autonomic and metabolic processes, suggesting that it is involved in integration of cerebral activity with homeostatic processes, as well as in motivation and reward, as delta also increases during hunger, sexual arousal, and sustained pain [119]. Delta activity is further related to attention, salience detection, and subliminal perception, consistent with meditative states and absorption [116, 119, 120], such as in the case of Yoga Nidra [121]<sup>3</sup> .

In-line with previous research linking delta waves in meditative states [125], a recent study examined the effects of the OVO Whole-Body Perceptual Deprivation (OVO-WBPD) chamber effects on absorption in experienced meditators. The OVO, an altered sensory environment, is in the form of a human-sized egg ("uovo" means egg in Italian), within which the subject cannot easily perceive spatial coordinates. Based on the Sphere Model of Consciousness, the OVO-WBPD was specifically built with the aim of facilitating an immersive experience and an increased state of *presence* [11]. Ben-Soussan et al. [120], who studied participants who were instructed to "rest as best as they can" in the OVO chamber, found an increased state of absorption, which was accompanied by enhanced delta and lower theta activity, as well as beta (13–20 Hz) activity, peaking in the insula. These results may suggest an enhanced effort to sensory-integrate interoceptive signals.

In addition to the insula [120], theta was further linked to another main area of the salience network, namely, the anterior cingulate [126–131]. While DMN activity is negatively correlated with both hypnosis and theta activity [129–131], the salience network is thought to support the detection of subjectively important events and the mobilization of attentional and working memory resources in the service of goal-directed behavior [132–134].

*Hypnotherapy and Hypnosis*

([56], p. 44).

**2.2 Meditation**

beta on the other [106].

they are different aspects of the same process ... This is a critical problem for future research. …we might question whether it is plausible to accept that theta activity observed during zazen concentration in experienced meditators indexes psychological processes that are similar to those observed in college-age volunteers when concentrating on a mental arithmetic problem." Thus, even though, as White, et al. ([105], p. 98) have noted, the "correlation between baseline theta and hypnotizability has been described as a robust finding in the literature, proposed to result from attentional differences between high and low susceptibility groups," without a close analysis of how such theta activity is related to the actual performance of those scoring low or high on absorption, we will remain with the problem underlined by Schacter [104]. What is promising is that "findings showing differences between highs and lows in both the *patterns* of associations between EEG-assessed bandwidth activity and subjects' phenomenological experience of hypnosis … and in the brain *areas* (source locations) associated with theta and beta activity…."

Speaking of beta, it was further found that the hypnotic depth and increased imagery and exceptionality of the hypnotic experience in highly suggestible individuals were related to fast frequencies, including beta and gamma, while the lows exhibited negative correlations between imagery on the one hand and theta and

In this context, it should also be kept in mind that beta oscillatory activity is likely to have a functional role in response selection, resembling attentional modulation of alpha activity [107]. Beta modulation was found also following "animal

The modulation depended on type of induction and session number [108, 109], supporting previous evidence that beta power has also been implicated in broader cognitive processes [107] in addition to movement and response inhibition [107].

Meditators have been found to score higher on trait absorption than controls [95, 110]. In addition, increased theta and alpha power, reflecting activity of multifunctional neuronal networks and differentially associated with orienting, attention, memory, affective, and cognitive processing, is evident in meditators [80]. Altered theta and alpha activity has consistently been reported following meditation [111]. In fact, numerous studies conducted with Western meditators, usually having less than 10 years' experience, have reported increased power and coherence in the alpha and theta frequency bands during meditation practice [39, 111, 112]. Increased gamma power has also been reported in studies with

Consistent with previous meditation research (for review see [115]), also Berman and Stevens [116] found increased delta (0–4 Hz), theta, and alpha activity during meditation. When differentiating between general meditation and nondual states (in which the participant transcends the separation between self and other), the opposite trend was observed for gamma, which was higher during the meditation sessions in entirely compared to the nondual state [116]. Similarly, Berkovich-Ohana et al. [73], who examined three levels of mindfulness expertise and controls, found that mindfulness practitioners generally exhibited reduced resting-state frontal low gamma power as compared to controls, as well as decreased resting-state gamma functional connectivity representing DMN deactivation in the long-term practitioners, suggesting a trait/long-lasting effect of reduced mind-wandering and self-related processing [73, 117]. In addition, creativity, as measured by ideational fluency and flexibility, which were higher in the long-term practitioners than

hypnosis," also known as "tonic immobility" or "immobility reflex".

advanced meditative practitioners [38, 73, 113, 114].

**78**

<sup>3</sup> Yoga Nidra is defined as a "state in which an individual demonstrates all the symptoms of deep, non-REM sleep, including delta brain waves, while simultaneously remaining fully conscious [121]. In addition, it is important to note that while meditation spindles have similar amplitudes to those in sleep, all other parameters are significantly different, with more-experienced subjects displaying high-voltage slow waves reminiscent, but significantly different, to the slow waves of deeper stages of non-REM sleep [122]. In addition, they also differ from slow delta activity in anesthesia which is notably less rhythmic and coherent [122]. Most importantly, the main regions of interest are notably different to those in sleep [122, 123]. More specifically, the significant presence of limbic sources in meditation support the hypothesis of the effects of meditation on memory and spatial and temporal orientation, and consequently to the ventral and dorsal streams of attention and feeling- and salience-based, respectively [122]. The electrophysiological change induced by these type of training, together with the ability to remain consciously aware while producing delta waves, is believed to be associated with attaining a highly stabilized state of higher consciousness [121, 124] and the integration of transcendental experiences in both waking, dreaming, and sleeping [125].

As in the case of perceptual deprivation, different meditative states have also been found to be related to decreased DMN activity [73, 135–137]. Similarly, hypnosis was found to be related to decreased DMN activity [138] and suspending habitual modes of attention and achieving refined states of meta-awareness [139]. In fact, hypnotic induction increased subjective ratings of attentional absorption and decreased ratings of mind-wandering. Moreover, these changes were associated with decreased DMN activity and increased activity in prefrontal attention networks [138].
