On The Methodology Of EEG Analysis
During Altered States Of Consciousness

By

Emil Jovanov

e-mail: jovanov@ieee.org

Electrical and Computer Engineering Dept.
The University of Alabama in Huntsville
Huntsville, AL 35899

Abstract

Introduction

Relation between EEG and gross neurophysiological changes in states of consciousness (alertness vs. sleep, sleep phases, coma, epileptic seizures, etc.) is well established and analyzed [1-4]. The situation is somewhat vague for subtle changes, but we believe that every subtle change generates evident physical equivalent (and vice versa). Altered states of consciousness as extreme cases are indispensable in studying nature of consciousness.

Successful neural network models of parts of neural system inspired so called “connectionists” approach that led to the conclusion that consciousness is “in fact no more than behavior of a vast assembly of nerve cells and their associated molecules” [5]. However, the largest problem with this approach is still explanation how brain integrates fragments of information derived from highly specialized set of neurons to create unity of perception and thought. This problem is called binding problem. The above approach can hardly explain how can we perceive gestalts from a large amount of sensory information almost instantly.

The second approach is based on neural fields. In this model, the electromagnetic field of brain activity binds together particular parts of information [6-10]. Brain wave patterns therefore represent internal language of the brain and create local resonance (see Adey, John, Basar, and Leinfellner in [4]). Strong support for this approach is derived from the theory of coupled oscillators and spontaneous synchronization of biological systems [11]. Deterministic chaos is frequently used in explaining brain dynamics through the last decade. Moreover, chaotic systems are capable of producing novel activity patterns. That feature may influence brain’s creativity and trial-and-error problem solving.

We believe that certain pattern(s) of EM field activity represent basis from which different states of consciousness arise. Our hypothesis is that those patterns, although subtle, could be detected in brain electrical activity. In this paper, we present framework of analysis that could be used to characterize subtle EEG changes.

Generic model

• Perception is input block, processing sensory inputs (vision, sound, touch, ...).
• Action generates different outputs (thoughts, emotions, physical actions, ...)
• Conscious processing block interacts with both blocks and influences their activity according to the genetic heritage and the history of processing (sequence of inputs and action feedback representing experience). Some of its functions are simple connections between neurons (reflexes for example), and some emerge as complex interactions.

In spite of the fact that model of such simplicity must have high complexity elements (in this case conscious processing block), it can point out very important aspects of system functionality.

Figure 1: Generalized psycho-physiological model of the Self

Extreme states of consciousness are mostly related to the modified functionality of Perception block. Its output is changed by overloading senses, sensory deprivation or by changing its functionality (drug admission for example) [12]. Having in mind that during these states Action block exhibits rather altered output than its cessation, we can draw a conclusion that our model must have either internal generator or set of inputs that is not dependent on senses. We will introduce both possibilities in our model:

1. Internal signal generators within the Conscious processing block, represented as a white circle.
2. Extrasensory inputs as a means of communication with environment. They are represented as a set of separated inputs coming to the shaded part of Perception block.

Internal signal generators are set of physiological control loops within the organism, such as heart or breath control loop. Their fields influence significantly course of conscious processing, but their function is also influenced by the overall conscious state. The breath control loop is exceptionally important as it can be easily consciously controlled. It was shown that a mixture of combined yogic practices of breathing and relaxation (Santhi Kriya) increased alpha activity both in occipital and pre-frontal areas of the brain denoting an increase of calmness [13].

Extrasensory inputs may help in explaining most of psychic phenomena [14]. If electromagnetic (EM) field plays crucial role in explaining higher functions of conscious processing, then inter-personal influence of particular EM field must be taken into account. One can argue that the intensity of such field is negligible to induce any action. However, we should have in mind that basic processes within the brain are based on resonance [10], and that even slow intensity field may “provoke” resonant patterns of activity [15]. Framework for this analysis is given through the theoretical model of Dejan Rakovi. [16-19].

Throughout our research we are looking for the scientific evidence of both generators in our model, and characterization of their influence on consciousness. We believe that answers to these questions may offer clues for understanding very nature of consciousness.

3. EEG changes during altered state of consciousness

Most of research associated with the changes in brain electrical activity (BEA) in altered state of consciousness are related to meditation [22-29]. The most important features of EEG changes related to meditation are:

1. Establishing alpha activity in spite of open eyes (Hirai [22])
2. Increased amplitude of alpha activity (Hirai [22], Banquet [23,24], Wallace [25])
3. Slower frequency of alpha rhythm (Hirai [22], Banquet [23,24], Wallace [25]
4. Rhythmical theta waves (Hirai [22], Banquet [23,24], Wallace [25]
5. Increased synchronization (hypersynchronization - Banquet [23,24])
6. Dissociation of perception from the external sense organs (Hirai [22], Ray [27])
7. Transcendent signal (Ray [27,28])
8. Occasional fast wave activity (Banquet [24], Das and Gastaut [25], and Ray [27])

The first four changes are reported during the study of EEG changes related to Zen meditation [22]. Kasamatsu and Hirai ranked the changes in this order and find out that the changes directly depend on mental state and experience in meditation. During zazen (Zen meditation) alpha was slowing to 7-8 Hz, and rhythmical theta waves at six to seven cycles per second appeared in the last phase (attained only by skilled monks with long meditation experience).

In addition to the standard frequency bands, Ray has found so called “focused arousal” frequency component at 38Hz. This frequency component was found during the Dharana stage of Rajayoga [26]. Ray supposed that it could represent possible functional component in the process of attention (Dharana means holding the mind at a certain point).

Changed perception during meditation is frequently reported. Subjects usually define it as a relaxed awareness with stable reception. We defined this state as dissociation of perception from the external sense organs. Quantitative investigation of this phenomenon is performed by Hirai, and alpha block dehabituation was found [22].

Particularly hard problem is analysis of transcendent signal. Ray defined it as a signal that is not bound to the time frame by any law of time domain [26]. He investigated transcendent signal in relation to the highly amused states of a child as well as state of deep aesthetic appreciation [27]. However, the transcendency is likely to be correlated with the clock of the organic system. These states are characterized by large number of impulses (spikes), and increased low frequency waves (theta and specially delta waves).

Fast wave activity was occasionally reported [24,25,27]. Banquet identified synchronous beta waves from all brain regions of almost constant frequency and amplitude [24]. That activity was found at four advanced meditants during the subjectively reported deepest meditation. Das and Gastaut performed electroencephalographic examination of seven yogis and observed that as the meditation progressed the alpha waves gave way to fast-wave activity at the rate of 40-45Hz, and that these waves subsided with a return of the slow alpha and theta waves [25]. Ray has found unusually large activity in the frequency range 16-18Hz, during highly amused states as well as state of deep aesthetic appreciation [27].

To the best of our knowledge EEG changes related to the healing process are rarely investigated. Zhang reported the EEG alpha activity during the Qi Gong state that occurred predominantly in the anterior regions. The peak frequency of EEG alpha rhythm was slower than the resting state, and the change of EEG during Qi Gong between anterior and posterior half had negative correlation. It can be seen that reported changes are very similar to the previously described changes during the meditation.

Proposed Methodology

Figure 2: Block diagram of adopted methodology

The analysis is divided in two parts: static and dynamic.

The analysis starts by expert’s off-line manual artifact removing. In spite of some promising results in automatic artifact removal, manual removing using expert's knowledge is still preferred method in analysis. Then, topographic maps of artifact-free signal are built to indicate channels that have dominant activity in certain frequency bands (delta, theta, alpha, beta, etc.). The most interesting EEG channels are used for further signal processing procedures (spectral, coherence, wavelet, chaos and other analyses).

Then, on selected channels we perform dynamic analysis by constructing graphs with temporal dependencies of selected parameters (spectrogram, dominant band frequency, animation of topographic maps, coherence, ...).

On the other hand, dynamic analysis can indicate time intervals with significant changes of basic parameters (mean frequency, intensity, etc.), which are then subjected to additional static analysis.

According to our experience this interaction between static and dynamic analysis yields the best characterization of underlying neurophysiological changes.

In addition, interdependence analysis provides subtle information on simultaneous changes in brain electrical activity recorded from two subjects in the interactive state of mind.

Although the frequency domain analysis represents indispensable signal analysis procedure, we have found very useful time-domain analysis on different frequency band limited signals. It emphasizes both short-time signal changes, as well as statistical properties of the signal.

Certain frequency bands may indicate activity on different hierarchical levels, as depicted in Table 1. Source of activity in gamma, beta and alpha frequency band is thoroughly investigated, and we introduce hypothetical framework of analysis for the activity in theta, delta and sub-delta bands. Our hypothesis follows direction of the higher three bands that lower frequency represents higher level of integration, i.e. information binding. Therefore, activation in certain frequency band may indicate activity on the equivalent consciousness level. The proposed scheme may correspond with Jung’s structure “ego-consciousness-individual unconsciousness-collective unconsciousness”.

Table 1: Possible sources of activity in certain EEG frequency bands