Brainstem auditory-evoked potentials in two meditative mental states

A Critical Analysis on Characterizing the Meditation Experience Through the Electroencephalogram

Meditation practices, originated from ancient traditions, have increasingly received attention due to their potential benefits to mental and physical health. The scientific community invests efforts into scrutinizing and quantifying the effects of these practices, especially on the brain. There are methodological challenges in describing the neural correlates of the subjective experience of meditation. We noticed, however, that technical considerations on signal processing also don't follow standardized approaches, which may hinder generalizations. Therefore, in this article, we discuss the usage of the electroencephalogram (EEG) as a tool to study meditation experiences in healthy individuals. We describe the main EEG signal processing techniques and how they have been translated to the meditation field until April 2020. Moreover, we examine in detail the limitations/assumptions of these techniques and highlight some good practices, further discussing how technical specifications may impact the interpretation of the outcomes. By shedding light on technical features, this article contributes to more rigorous approaches to evaluate the construct of meditation.

Evolution from four mental states to the highest state of consciousness: A neurophysiological basis of meditation as defined in yoga texts

This chapter provides a theoretical introduction to states of consciousness and reviews neuroscientific investigations of meditation. The different states of consciousness consist of four mental states, i.e., cancalata (random thinking), ekagrata (non-meditative focusing), dharna (focused meditation), and dhyana (meditation) as defined in yoga texts. Meditation is a self-regulated mental process associated with deep relaxation and increased internalized attention. Scientific investigations on meditation reported changes in electrophysiological signals and neuroimaging measures. But most outcomes of meditation studies showed inconsistent results, this may be due to heterogeneity in meditation methods and techniques evolved in the last 200 years. Traditionally, the features of meditation include the capacity to sustain a heightened awareness of thoughts, behaviors, emotions, and perceptions. Generally, meditation involves non-reactive effortless monitoring of the content of experience from moment to moment. Focused meditation practice involves awareness on a single object and open monitoring meditation is a non-directive meditation involved attention in breathing, mantra, or sound. Therefore, results of few empirical studies of advanced meditators or beginners remain tentative. This is an attempt to compile the meditation-related changes in electrophysiological and neuroimaging processes among experienced and novice practitioners.

Directional brain networks underlying OM chanting

OM chanting is an ancient technique of Indian meditation. OM chanting is associated with an experience of relaxation, changes in autonomic balance and deactivation of limbic brain regions. While functional localization is important, how brain regions interact with each other has been shown to underlie various brain functions. Therefore, in this study, we tested the hypothesis that there is reduced communication between deactivated regions during OM chanting. In order to do so, we employed multivariate autoregressive model (MVAR) based Granger causality to obtain directional connectivity between deactivated regions. fMRI scans of 12 right handed healthy volunteers (9 Men) from a previously published study was used in which participants performed OM chanting and a control condition in a block design. We found that outputs from insula, anterior cingulate and orbitofrontal cortices were significantly reduced in OM condition. Of interest is the reduction of outputs from these regions to limbic area amygdala. Modulation of brain regions involved in emotion processing and implicated in major depressive disorder (MDD) raises a potential possibility of OM chanting in the treatment of MDD.

A selective review of dharana and dhyana in healthy participants

Attention is an important part of the process of meditation. Traditional Yoga texts describe two stages of meditation which follow each other in sequence. These are meditative focusing (dharana in Sanskrit) and effortless meditation (dhyana in Sanskrit). This review evaluated eight experimental studies conducted on participants in normal health, who practiced dharana and dhyana. The studies included evaluation of autonomic and respiratory variables, eLORETA and sLORETA assessments of the EEG, evoked potentials, functional magnetic resonance imaging, cancellation task performance and emotional intelligence. The studies differed in their sample size, design and the method of practicing dharana and dhyana. These factors have been detailed. The results revealed differences between dharana and dhyana, which would have been missed if the two stages of meditation had not been studied separately.

Long Latency Auditory Evoked Potentials during Meditation

The auditory sensory pathway has been studied in meditators, using midlatency and short latency auditory evoked potentials. The present study evaluated long latency auditory evoked potentials (LLAEPs) during meditation. Sixty male participants, aged between 18 and 31 years (group mean±SD, 20.5±3.8 years), were assessed in 4 mental states based on descriptions in the traditional texts. They were (a) random thinking, (b) nonmeditative focusing, (c) meditative focusing, and (d) meditation. The order of the sessions was randomly assigned. The LLAEP components studied were P1 (40-60 ms), N1 (75-115 ms), P2 (120-180 ms), and N2 (180-280 ms). For each component, the peak amplitude and peak latency were measured from the prestimulus baseline. There was significant decrease in the peak latency of the P2 component during and after meditation (P<.001; analysis of variance and post hoc analysis with Bonferroni adjustment). The P1, P2, and N2 components showed a significant decrease in peak amplitudes during random thinking (P<.01; P<.001; P<.01, respectively) and nonmeditative focused thinking (P<.01; P<.01; P<.05, respectively). The results suggest that meditation facilitates the processing of information in the auditory association cortex, whereas the number of neurons recruited was smaller in random thinking and non-meditative focused thinking, at the level of the secondary auditory cortex, auditory association cortex and anterior cingulate cortex.

Neurophysiological Effects of Meditation Based on Evoked and Event Related Potential Recordings

Evoked potentials (EPs) are a relatively noninvasive method to assess the integrity of sensory pathways. As the neural generators for most of the components are relatively well worked out, EPs have been used to understand the changes occurring during meditation. Event-related potentials (ERPs) yield useful information about the response to tasks, usually assessing attention. A brief review of the literature yielded eleven studies on EPs and seventeen on ERPs from 1978 to 2014. The EP studies covered short, mid, and long latency EPs, using both auditory and visual modalities. ERP studies reported the effects of meditation on tasks such as the auditory oddball paradigm, the attentional blink task, mismatched negativity, and affective picture viewing among others. Both EP and ERPs were recorded in several meditations detailed in the review. Maximum changes occurred in mid latency (auditory) EPs suggesting that maximum changes occur in the corresponding neural generators in the thalamus, thalamic radiations, and primary auditory cortical areas. ERP studies showed meditation can increase attention and enhance efficiency of brain resource allocation with greater emotional control.

Shirodhara: A psycho-physiological profile in healthy volunteers

Background:

Shirodhara is a classical and a well-established ayurvedic procedure of slowly and steadily dripping medicated oil or other liquids on the forehead. This procedure induces a relaxed state of awareness that results in a dynamic psycho-somatic balance.

Objectives:

The objective of the study is to evaluate the psychological and physiological effects of Shirodhara in healthy volunteers by monitoring the rating of mood and levels of stress, electrocardiogram (ECG), electroencephalogram (EEG), and selected biochemical markers of stress.

Materials and Methods:

The study was conducted in the human pharmacology laboratory. The study design was open labeled, comparing the baseline variables with values after Shirodhara. The subjects (n = 16) chosen were healthy human volunteers who gave an informed consent. Shirodhara was preceded by Abhyanga – whole body massage. The Shirodhara method was standardized for rate of dripping with peristaltic pump and temperature was controlled with a thermostat. Mood and stress levels were assessed by validated rating scales. The pre- and post-Shirodhara ECG and EEG records were evaluated.

Results:

Student's paired “t” test was applied to the means + SE of the variables to calculate statistical significance at P <0.05. There was a significant improvement in mood scores and the level of stress (P <0.001). These changes were accompanied by significant decrease in rate of breathing and reduction in diastolic blood pressure along with reduction in heart rate. The relaxed alert state, after Shirodhara, was co-related with an increase in alfa rhythm in EEG.

Conclusion:

A standardized Shirodhara leads to a state of alert calmness similar to the relaxation response observed in meditation. The clinical benefits observed with Shirodhara in anxiety neurosis, hypertension, and stress aggravation due to chronic degenerative diseases could be mediated through these adaptive physiological effects.

Science of the mind: ancient yoga texts and modern studies

The practice of yoga is gaining in popularity with a wide range of practices. Recent research and descriptions from the ancient texts are often concurrent with regard to the effects of the practice, taking into account expected differences between modern scientific terms and those used in the original texts. Voluntarily regulated yoga breathing practices form a bridge between physical and mental changes. The voluntarily regulated yoga breathing has distinct effects on metabolism, the autonomic nervous system, higher brain functions, and mental state. The effects of meditation on the nervous system and mental state are even clearer.

Mid-latency auditory evoked potentials in 2 meditative states

Mid-latency auditory evoked potentials (MLAEPs) were assessed in 60 participants during 4 mental states described in traditional yoga texts. These 4 mental states are random thinking, nonmeditative-focused thinking, meditative focusing, and meditation. Assessments were made before (5 minutes), during (20 minutes), and after (5 minutes) each of the 4 states, on 4 separate days. There were prolonged latencies of 2 MLAEPs components, the Na and Pa waves during meditation (P < .05, post hoc analyses following analysis of variance [ANOVA]), suggesting that auditory information transmission at the level of the medial geniculate and primary auditory cortex (ie, the neural generators corresponding to the Na and Pa waves) was delayed. Hence, meditation influenced MLAEPs, while meditative focusing did not.

Meditation and attention: a comment on a recent article

Meditation and attention are considered associated in different ways. For example, contemporary concepts state that to meditate, a practitioner has either to (i) focus attention on the object of meditation (FA) or (ii) maintain vigilance and disengage their attention consciously from all distracters (OM). The Indian sage Patanjali (circa 900 B.C.), mentioned that there are two stages of meditation, which differ subtly from the descriptions of FA and OM. One stage is called dharana, or focusing attention on the object of meditation. Another stage is called dhyana, during which all thoughts remain effortlessly directed to the object of meditation, excluding all other thoughts. Vigilance and attention are not required during dhyana, which is the actual phase of meditation. In a previous study, participants who practiced dharana performed better in a task for selective attention than those who practiced dhyana. Brainstem auditory evoked potential changes during the two states differed. Descriptions of yoga practices from ancient texts can give added insights about meditation and attention, supported by objective assessments.