Prof. J.P.N. Mishra
To examine changes in brain physiology during a chanting meditation practice using cerebral blood flow single-photon emission computed tomography, Khalsa DS (2009) scientifically investigated cerebral blood flow changes during chanting meditation. Single-photon emission computed tomography scans were acquired in 11 healthy individuals during either a resting state or meditation practice randomly performed on two separate days. Statistical parametric mapping analyses were conducted to identify significant changes in regional cerebral blood flow (RCBF) between the two conditions. When the meditation state was compared with the baseline condition, significant RCBF increases were observed in the right temporal lobe and posterior cingulated gyrus, and significant RCBF decreases were observed in the left parietotemporal and occipital gyrus. The results offer evidence that this form of meditation practice is associated with changes in brain function in a way that is consistent with earlier studies of related types of meditation as well as with the positive clinical outcomes anecdotally reported by its users.
Does meditation enhance cognition and brain plasticity? Xiong GL (2009) stated that meditation practices have various health benefits including the possibility of preserving cognition and preventing dementia. While the mechanisms remain investigational, studies show that meditation may affect multiple pathways that could play a role in brain aging and mental fitness. For example, meditation may reduce stress-induced Cortisol secretion and this could have neuroprotective effects potentially via elevating levels of brain derived neurotrophic factor (BDNF). Meditation may also potentially have beneficial effects on lipid profiles and lower oxidative stress, both of which could in turn reduce the risk for cerebrovascular disease and age-related neurodegeneration. Further, meditation may potentially strengthen neuronal circuits and enhance cognitive reserve capacity. These are the theoretical bases for how meditation might enhance longevity and optimal health. Evidence to support a neuroprotective effect comes from cognitive, electroencephalogram (EEG), and structural neuroimaging studies. In one cross-sectional study, meditation practitioners were found to have a lower age-related decline in thickness of specific cortical regions. However, the enthusiasm must be balanced by the inconsistency and preliminary nature of existing studies as well as the fact that meditation comprises a heterogeneous group of practices. Key future challenges include the isolation of a potential common element in the different meditation modalities, replication of existing findings in larger randomized trials, determining the correct "dose," studying whether findings from expert practitioners are generalizable to a wider population, and better control of the confounding genetic, dietary and lifestyle influences.
Czisch M (2009) studied "Acoustic oddball during NREM sleep: a combined EEG/fMRI study. A condition vital for the consolidation and maintenance of sleep is generally reduced responsiveness to external stimuli. Despite this, the sleeper maintains a level of stimulus processing that allows responding to potentially dangerous environmental signals. The mechanisms that sub serve these contradictory functions are only incompletely understood. Using combined EEG/fMRI we investigated the neural substrate of sleep protection by applying an acoustic oddball paradigm during light NREM sleep. Further, we studied the role of evoked K-complexes (KCs), an electroencephalographic hallmark of NREM sleep with a still unknown role for sleep protection. Our main results were:
- Other than in wakefulness, rare tones did not induce a blood oxygenation level dependent (BOLD) signal increase in the auditory pathway but a strong negative BOLD response in motor areas and the amygdala.
- Stratification of rare tones by the presence of evoked KCs detected activation of the auditory cortex, hippocampus, superior and middle frontal gyri and posterior cingulate only for rare tones followed by a KC.
- The typical high front central EEG deflections of KCs were not paralleled by a BOLD equivalent. We observed that rare tones lead to transient disengagement of motor and amygdala responses during light NREM sleep.
We interpret this as a sleep protective mechanism to delimit motor responses and to reduce the sensitivity of the amygdala towards further incoming stimuli. Evoked KCs are suggested to originate from a brain state with relatively increased stimulus processing, revealing an activity pattern resembling novelty processing as previously reported during wakefulness. The KC itself is not reflected by increased metabolic demand in BOLD based imaging, arguing that evoked KCs result from increased neural synchronicity without altered metabolic demand
Swarnkar V (2009) studied "A state transition-based method for quantifying EEG sleep fragmentation". Sleep fragmentation is the predominant factor causing excessive daytime sleepiness in diseases such as sleep apnea and periodic leg movement syndrome. The reference standard for quantifying sleep fragmentation is the arousal index (Arl), which is defined as the average number of arousals per hour of sleep. Arousal scoring is tedious and subjective resulting in considerable inter- and intra-ratter variability. Moreover, Arl is only weakly correlated with other indicators of sleep fragmentation such as the total sleep time (TST) and the sleep efficiency (SE). This introduces consistency problems, making the Arl difficult to interpret in practice. In this article, we address these issues by proposing a novel measure of sleep fragmentation termed the weighted-transition sleep fragmentation index (chi). This new measure is derived by capturing the different sleep states transitions and assigning weights to them. A significant correlation was found between chi and all other indices of sleep fragmentation (r = 0.72, sigma = 0.0001, r = -0.59, sigma = 0.001, r = -0.72, sigma = 0.0001, respectively, for Arl, TST and SE. These results suggest that chi is an accurate and useful tool for clinical practice.
Tei S (2009). Meditators and Non-Meditators: EEG Source Imaging During Resting. Many meditation exercises aim at increased awareness of ongoing experiences through sustained attention and at detachment, i.e., non-engaging observation of these ongoing experiences by the intent not to analyse, judge or- expect anything. Long-term meditation practice is believed to generalize the ability of increased awareness and greater detachment into everyday life. We hypothesized that neuroplasticity effects of meditation (correlates of increased awareness and detachment) would be detectable in a no-task resting state. EEG recorded during resting was compared between Qigong meditators and controls. Using LORETA (low resolution electromagnetic tomography) to compute the intracerebral source locations, differences in brain activations between groups were found in the inhibitory delta EEG frequency band. In the meditators, appraisal systems were inhibited, while brain areas involved in the detection and integration of internal and external sensory information showed increased activation. This suggests that neuroplasticity effects of long-term meditation practice, subjectively described as increased awareness and greater detachment, are carried over into non-meditating states.
Beauregard M (2009) studied brain activity in near-death experiences during a meditative state. In two separate experiments, brain activity was measured with functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) during a Meditation condition and a Control condition. In the Meditation condition, participants were asked to mentally visualize and emotionally connect with the "being of light" allegedly encountered during their "near-death experience". In the Control condition, participants were instructed to mentally visualize the light emitted by a lamp. In the fMRI experiment, significant loci of activation were found during the Meditation condition (compared to the Control condition) in the right brainstem, right lateral orbitofrontal cortex, right medial prefrontal cortex, right superior parietal lobule, left superior occipital gyrus, left anterior temporal pole, left inferior temporal gyrus, left anterior insula, left Para hippocampal gyrus and left substantia nigra. In the EEG experiment, electrode sites showed greater theta power in the Meditation condition relative to the Control condition at FP1, F7, F3, T5, P3, 01, FP2, F4, F8, P4, Fz, Cz and Pz. In addition, higher alpha power was detected at FP1, F7, T3 and FP2, whereas higher gamma power was found at FP2, F7, T4 and T5. The results indicate that the meditative state was associated with marked hemodynamic and neuroelectric changes in brain regions known to be involved either in positive emotions, visual mental imagery, attention or spiritual experiences.
Baijal S (2009) Theta activity and meditative states: spectral changes during concentrative meditation. Brain oscillatory activity is associated with different cognitive processes and plays a critical role in meditation. In this study, we investigated the temporal dynamics of oscillatory changes during Sahaj Samadhi meditation (a concentrative form of meditation that is part of Sudarshan Kriya yoga). EEG was recorded during sudarshan kriya yoga meditation for meditators and relaxation for controls. Spectral and coherence analysis was performed for the whole duration as well as specific blocks extracted from the initial, middle, and end portions of Sahaj Samadhi meditation or relaxation. The generation of distinct meditative states of consciousness was marked by distinct changes in spectral powers especially enhanced theta band activity during deep meditation in the frontal areas. Meditators also exhibited increased theta coherence compared to controls. The emergence of the slow frequency waves in the attention-related frontal regions provides strong support to the existing claims of frontal theta in producing meditative states along with trait effects in attentional processing. Interestingly, increased frontal theta activity was accompanied reduced activity (deactivation) in parietal-occipital areas signifying reduction in processing associated with self, space and, time.
Chiesa A (2009) Zen meditation: an integration of current evidence. Despite the growing interest in the neurobiological and clinical correlates of many meditative practices, in particular mindfulness meditations, no review has specifically focused on current evidence on electroencephalographic, neuroimaging, biological, and clinical evidence about an important traditional practice, Zen meditation. A literature search was conducted using MEDLINE, the ISI Web of Knowledge, the Cochrane collaboration database, and references of selected articles.
Randomized controlled and cross-sectional studies with controls published in English prior to May 2008 were included. Electroencephalographic studies on Zen meditation found increased alpha and theta activity, generally related to relaxation, in many brain regions, including the frontal cortex. Theta activity in particular seemed to be related to the degree of experience, being greater in expert practitioners and advanced masters. Moreover, Zen meditation practice could protect from cognitive decline usually associated with age and enhance antioxidant activity. From a clinical point of view, Zen meditation was found to reduce stress and blood pressure, and be efficacious for a variety of conditions, as suggested by positive findings in therapists and musicians. To date, actual evidence about Zen meditation is scarce and highlights the necessity of further investigations. Comparison with further active treatments, explanation of possible mechanisms of action, and the limitations of current evidence are discussed.
Tang YY (2009) Central and autonomic nervous system interaction is altered by short-term meditation. Five days of integrative body-mind training (IBMT) improves attention and self-regulation in comparison with the same amount of relaxation training. This paper explores the underlying mechanisms of this finding. We measured the physiological and brain changes at rest before, during, and after 5 days of IBMT and relaxation training. During and after training, the IBMT group showed significantly better physiological reactions in heart rate, respiratory amplitude and rate, and skin conductance response (SCR) than the relaxation control. Differences in heart rate variability (HRV) and EEG power suggested greater involvement of the autonomic nervous system (ANS) in the IBMT group during and after training. Imaging data demonstrated stronger subgenual and adjacent ventral anterior cingulate cortex (ACC) activity in the IBMT group. Frontal midline ACC theta was correlated with high-frequency HRV, suggesting control by the ACC over parasympathetic activity. These results indicate that after 5 days of training, the IBMT group shows better regulation of the ANS by a ventral midfrontal brain system than does the relaxation group. This changed state probably reflects training in the coordination of body and mind given in the IBMT but not in the control group. These results could be useful in the design of further specific interventions.
Qin Z (2009) A follow-up EEG study was conducted on a subject with 50 years of experiences in Qigong. Resting EEG at present showed frontally dominant alpha-1 as compared to occipital dominant alpha-2 described in 1962. During the Qigong practice alph-1 enhanced quickly and became far more prominent than 50 years ago. Compared with baseline, these activities remained to be higher at rest after the Qigong practice. These results suggest that extended practice in meditation may change the EEG pattern and its underlying neurophysiology. It remains to be explored as to what biological significance and clinical relevance do these physiological changes might mean.
Travis F, (2009) Effects of Transcendental Meditation practice on brain functioning and stress reactivity in college This randomized controlled trial investigated effects of Transcendental Meditation (TM) practice on Brain Integration Scale scores (broadband frontal coherence, power ratios, and preparatory brain responses), electro dermal habituation to 85-dB tones, sleepiness, heart rate, respiratory sinus arrhythmia, and P300 latencies in 50 college students. After pre-test, students were randomly assigned to learn TM immediately or learn after the 10-week post-test. There were no significant pre-test group differences. A MANOVA of students with complete data (N=38) yielded significant group vs treatment interactions for Brain Integration Scale scores, sleepiness, and habituation rates (all p<.007). Post hoc analyses revealed significant increases in Brain Integration Scale scores for Immediate-start students but decreases in Delayed-start students; significant reductions in sleepiness in Immediate-start students with no change in Delayed-start students; and no changes in habituation rates in Immediate-start students, but significant increases in Delayed-start students. These data support the value of TM practice for college students.
Cahn BR (2009) studied Meditation (Vipassana) and the P3a event-related brain potential. A three-stimulus auditory oddball series was presented to experienced vipassana meditators during meditation and a control thought period to elicit event-related brain potentials (ERPs) in the two different mental states. The stimuli consisted of a frequent standard tone (500 Hz), an infrequent oddball tone (1000 Hz), and an infrequent distracter (white noise), with all stimuli passively presented through headphones and no task imposed. The strongest meditation compared to control state effects occurred for the distracter stimuli: N1 amplitude from the distracter was reduced frontally during meditation; P2 amplitude from both the distracter and oddball stimuli were somewhat reduced during meditation; P3a amplitude from the distracter was reduced during meditation. The meditation-induced reduction in P3a amplitude was strongest in participants reporting more hours of daily meditation practice and was not evident in participants reporting drowsiness during their experimental meditative session. The findings suggest that meditation state can decrease the amplitude of neurophysiologic processes that sub serve attentional engagement elicited by unexpected and distracting stimuli. Consistent with the aim of vipassana meditation to reduce cognitive and emotional reactivity, the state effect of reduced P3a amplitude to distracting stimuli reflects decreased automated reactivity and evaluative processing of task irrelevant attention-demanding stimuli.
Vialatte FB (2008) studied EEG paroxysmal gamma waves during Bhramari Pranayama: A yoga breathing technique. Here we report that a specific form of yoga can generate controlled high-frequency gamma waves. For the first time, paroxysmal gamma waves (PGW) were observed in eight subjects practicing a yoga technique of breathing control called Bhramari Pranayama (BhPr). To obtain new insights into the nature of the EEG during BhPr, we analysed EEG signals using time-frequency representations (TFR), independent component analysis (ICA), and EEG tomography (LORETA). We found that the PGW consists of high-frequency biphasic ripples. This unusual activity is discussed in relation to previous reports on yoga and meditation. It is concluded this EEG activity is most probably non-epileptic, and that applying the same methodology to other meditation recordings might yield an improved understanding of the neurocorrelates of meditation.
Eskandari P (2008) Studied cognitive tasks using motor imagery have been used for generating and controlling EEG activity in most brain-computer interface (BCI). Nevertheless, during the performance of a particular mental task, different factors such as concentration, attention, level of consciousness and the difficulty of the task, may be affecting the changes in the EEG activity.
Accordingly, training the subject to consistently and reliably produce and control the changes in the EEG signals is a critical issue in developing a BCI system. In this work, we used meditation practice to enhance the mind controllability during the performance of a mental task in a BCI system. The mental states to be discriminated are the imaginative hand movement and the idle state. The experiments were conducted on two groups of subject, meditation group and control group. The time-frequency analysis of EEG signals for meditation practitioners showed an event-related desynchronization (ERD) of beta rhythm before imagination during resting state. In addition, a strong event-related synchronization (ERS) of beta rhythm was induced in frequency around 25 Hz during hand motor imagery. The results demonstrated that the meditation practice can improve the classification accuracy of EEG patterns. The average classification accuracy was 88.73% in the meditation group, while it was 70.28% in the control group. An accuracy as high as 98.0% was achieved in the meditation group.
SrinivasanN (2007) studied concentrative meditation enhances pre-attentive processing: a mismatch negativity study. The mismatch negativity (MMN) paradigm that is an indicator of preattentive processing was used to study the effects of concentrative meditation. Sudarshan Kriya Yoga meditation is a yogic exercise practiced in an ordered sequence beginning with breathing exercises, and ending with concentrative (Sahaj Samadhi) meditation. Auditory MMN waveforms were recorded at the beginning and after each of these practices for meditators, and equivalently after relaxation sessions for the nonmeditators.
Overall meditators were found to have larger MMN amplitudes than nonmeditators. The meditators also exhibited significantly increased MMN amplitudes immediately after meditation suggesting transient state changes owing to meditation. The results indicate that concentrative meditation practice enhances preattentive perceptual processes, enabling better change detection in auditory sensory memory.
Doraiswamy PM (2007) Does Meditation Enhance Cognition and Brain Longevity? Meditation practices have various health benefits including the possibility of preserving cognition and preventing dementia. While the mechanisms remain investigational, studies show that meditation may affect multiple pathways that could play a role in brain aging and mental fitness. For example, medication may reduce stress-induced Cortisol secretion and this could have neuroprotective effects potentially via elevating levels of brain derived neurotrophic factor (BDNF). Meditation may also potentially have beneficial effects on lipid profiles and lower oxidative stress, both of which could in turn reduce the risk for cerebrovascular disease and age-related neurodegeneration. Further, meditation may potentially strengthen neuronal circuits and enhance cognitive reserve capacity.
These are the theoretical basis for how medication might enhance longevity and optimal health. Evidence to support a neuroprotective effect comes from cognitive, electroencephalogram (EEG), and structural neuroimaging studies. In one cross-sectional study, meditation practioners were found to have a lower age-related decline in thickness of specific cortical regions. However, the enthusiasm must be balanced by the inconsistency and preliminary nature of existing studies as well as the fact that meditation comprises a heterogeneous group of practices. Key future challenges include the isolation of a potential common element in the different meditation modalities, replication of existing findings in larger randomized trials, determining the correct "dose," studying whether findings from expert practioners are generalizable to a wider population, and better control of confounding genetic, dietary and lifestyle influences.
Barnhofer T (2007) Effects of meditation on frontal alpha-asymmetry in previously suicidal individuals This study investigated the effects of a meditation-based treatment for preventing relapse to depression, mindfulness-based cognitive therapy (MBCT), on prefrontal alpha-asymmetry in resting electroencephalogram (EEG), a biological indicator of affective style. Twenty-two individuals with a previous history of suicidal depression were randomly assigned to either MBCT (N=10) or treatment-as-usual (TAU, N=12). Resting electroencephalogram was measured before and after an 8-week course of treatment. The TAU group showed a significant deterioration toward decreased relative left-frontal activation, indexing decreases in positive affective style, while there was no significant change in the MBCT group. The findings suggest that MBCT can help individuals at high risk for suicidal depression to retain a balanced pattern of baseline emotion-related brain activation.
A study on meditation: a new role for an old friend was conducted by Wright LD (2006). Meditation has been a spiritual and healing tradition for centuries. In 1972, Keith Wallace and Herbert Benson published a landmark article looking at meditation from a scientific perspective. The author reviewed their article, plus selected scientific literature on meditation since that time, to see if there was enough evidence to warrant the inclusion of meditation in the treatment protocols of serious disease. This review, plus an illustrative case study, demonstrated that such inclusion is warranted and further research is necessary.
