• mindfulness_meditation

Neuroscience of Meditation

Olivia Carolan, Shannon Stewart, Claire Varnai

Introduction

Meditation is a form of mental training that aims to improve an individual's core psychological capacities, such as attentional and emotional self-regulation. Mindful meditation is a non-judgemental attention to present-moment experiences. We analysed different studies that had explored meditations effect on brain shape and frequencies, pain receptors and depression. Through different research studies we evaluated the effects of mindful meditation (in those specific cases) on the brain and how the brain responds to the environment gathering information to make further inferences on what mindful meditation allows and what it affects are on brain processing. The studies we focus on involve how the brain structure can alter, pain reception, depression processing, and how meditation can be used to train neural synchrony.

Physiology Background

EEG is a tool utilized to understand the electrical activity in the brain. The electrical activity is the summation of postsynaptic activation states that determine the potential measured by the electrode. EEG detects the dipole caused by the dendrites perpendicular to the top of the skull.

Pain reception is through nociceptive free nerve endings, the action potential that is triggered from a painful stimulus is transmitted in two forms fast (A Delta) fibers, slow (C reception) fibers . The reason for the fast transmission is due to the flexor reflexes that removes affected body part away from the pain stimulus, and the slow is due slow spreading pain in emotional state causing drop of blood pressure, nausea. The fibers are in the thalamus and spinal cord which then get carried to the cortex.

The limbic system contains the hippocampus in which it’s main role is involved in middle term memory processing and more recently found emotional processing. The thalamus plays a role in signal modulation; receptors on the trunk are perceived where the signal is sent to the nucl. Cuneatus and gracilis where the fibers run to the opposite side of the thalamic nuclei from here they are called the relay nuclei. The relay nuclei allow information from the spinal cord to be taken to the thalamus which include the ventral postero-lateral nuclei, and the postero medial nuclei. The nuclei modifies the information from the receptive field through interneurons so that the localisation of the stimulus is better grasped, the signal is then sent to the cortex. Grey matter can be found in different areas in the body the spinal cord and the cerebral cortex. Grey matter is made up of neuron cell bodies. The main function of grey matter is to transmit sensory information from grey matter cells and organs and then pass it to areas of the brain that are involved in sensory info processing.

Functional magnetic resonance imaging (fMRI) is similar to MRI which is a noninvasive test that uses a strong magnetic field and radio waves to create detailed images of the body. Due to the coupling of cerebral blood flow and neuronal activity, fMRI detects brain activity in specific areas based on increased blood flow.

Brain structure changes correlated from Mindful meditation (hippocampus and orbitofrontal cortex, larger grey matter)

The study (Luders et al, 2009) was designed to examine the effects of mindful meditation on brain structure on two levels. This study was conducted using MRI high-resolution images, on 22 active mediating participants and 22 controls. Each group had 9 men and 13 women (age 30-71). The active mediating participants had to be

practicing mediation long termly this being classified at 5-46 years, mediating 10-90 minutes per day. The forms of mediation varied for the individuals. The MRI was paired with Voxel-based morphometry (Ashburner and Friston, 2000), to examine the focal differences in brain structure through determining the volume of specific areas in the brain. The technique was used to show the total volume of the brain, volume of grey and subcortical regions of interest. The study also used a novel parcellation technique (Tu et al, 2008) which divides the brain into certain areas due to structure and function, establishing 1) left inferior temporal gyrus; (2) right insula; (3) right hippocampus; (4) right superior frontal gyrus; and (5) right middle frontal gyrus. The study further wanted to reveal the brain structure differences based on the length a participant has been meditating. Therefor, the active mediating group was split into 2 groups, one including individuals who have been meditating for more than 20 years (9 people) and the other less than 20 years (13 people).

The results showed that there was a increased volume of grey matter in the right orbito-frontal cortex, right thalamus, left inferior temporal gyrus (21.54 vs. 21.38 cm3 ) for the mediating group compared to the controls. In respect to total brain volume or total grey matter volume, or the volume of subcortical areas of interested there was no difference in volume between the mediators and the controls except for the volume of the right hippocampus (3.73 cm3 vs. 3.53cm3 ). When comparing brain volumes to based on the length of years mediating there was significant difference between the groups.

• The orbito-frontal cortex has been shown to control emotional regulation, specifically negative emotion (Quirk and Beer, 2006) and behavior alteration (Brown and Ryan, 2003). Thalamus has been linked to controlling sensory information processing for example increasing focus during meditation (Newberg and Iversen, 2003). Inferior temporal gyrus researched to show its role in the pleasure (Holzel et al, 2008). Hippocampus research has revealed its function in emotional processing, in regard to mediation the positive emotions, and attention abilities (Davidson and colleagues, 2000). The hippocampus holds the ability to restore new neurons (Eriksson et al, 1998). From the results we can conclude that mindful meditation can have a positive correlation the enlargement of specific brain areas most importantly the orbito-frontal cortex and the hippocampus that can be linked to positive emotion production, emotional regulation, and mindful behavior. Again it is important to state that this is not proof for causation, simply correlation.

Self-induced high-amplitude gamma synchrony

Meditation has been analyzed to detect its effect on our brain frequencies. Researchers studied how people who regularly practice meditation can self-induce high-amplitude gamma synchrony. Neural synchrony has been previously examined as a gamma-band frequency (25-70HZ) in mental processes involved in attention, learning and conscious perception. These synchronizations of oscillating neural dischargers are thought to be crucial in the composition of transient networks that combine circulating neural processes into highly ordered cognitive and affective functions, which could induce synaptic changes.

The subjects in this research were long-term Buddhist practitioners who had practiced meditation for at least over 15 years, eight hours a day, and controls, who practiced meditation one hour a day for a week before data collection via EEG. Meditation has been shown to alter the ratio between gamma-band activity to slow oscillatory activity. It is initially higher at the resting baseline before meditation in the Buddhist practitioners than the controls. This difference continues to increase drastically during meditation. The amplitude of gamma oscillations is related to the size of the oscillating neural population and degree of precision with which cells oscillate, this study suggest that massive distributed neural assemblies are synchronized with a high temporal precision in the fast frequencies during the meditative state. The gradual increase of gamma activity during meditation corresponds with the view that neural synchronization needs time to develop proportional to the size of the synchronized neural assembly (Campbell et al, 1999). Overall, this study was consistent with the idea that attention processes, which gamma-band EEG synchronization can demonstrate, are flexible skills that can be trained (Posner et al, 1997).

Limitations in the experiment included robust gamma-band oscillation and long-distance phase-synchrony. The researchers stated these could be due to the inconsistency of the meditation practices used in the study. Brain function will vary with different types of meditation. A further study was later conducted to investigate just that (Braboszcz et al, 2017) .

Researchers compared increased gamma brainwave amplitude between controls and three different meditation traditions. The three groups were Vipassana, Himalayan Yoga and Isha Shoonya. The meditation practices vary in concentration. Himalayan Yoga requires focused attention, using a mantra to maintain attention. Vipassana follows an open monitoring practice, with loose focus on somatosensory awareness aspect. Isha Yoga is an open awareness meditation with no specific object to focus on. Frequency ranges were defined by analyzing the spectral power from 2 to 110 Hz. Differences were noticed between the groups between the 60-110 Hz gamma frequency and 7-11 Hz alpha frequency range. The subjects were asked to meditate (MED) and to participate in an instructed mind-wandering practice (IMW), which is when the subject is relaxed but not in a meditative state. Gamma frequency band activity was analyzed by first assessing the two conditions of MED and IMW and the median 60-110 Hz gamma power over the frontal and parieto-occipital electrodes. They found significant effect of the group of the gamma power over parieto-occipital location but not over the frontal location. Post-hoc tests were done to compare the three meditator groups to the control group. Increased 60–110 Hz power over parieto-occipital electrodes was found in each group of meditators when compared to controls and additional increase over central and frontal electrodes was found for the Isha shoonya group only.

The researchers delve further into investigating the specific effects of the different meditation practices. They did this by comparing 10 minutes of breathing meditation with the last 10 minutes of the practitioners specific meditation. Both Himalayan yoga and Isha shoonya showed decreased 60–110 Hz power in meditation compared to breath focus. This effect was observed over centro-occipital electrodes for the Himalayan yoga and over fronto-central electrodes for the Isha shoonya group. The Vipassana group did not show any significant difference between breath focus and meditation in this frequency range.

Overall, all three groups experienced higher 60-110 Hz power than control group in MED and MED+IMW, and there was a trend for higher 60-110 Hz power than the control in IMW. HYT and ISY groups also had lower 60-110 Hz power in meditation than in breath focus, while VIP had no significant difference between MED and breath focus, but it did have enhanced alpha power, having a higher 7-11 Hz power during MED and IMW than all other groups. The study proved that brain activity can vary depending on the type of meditation practice done; however, all three practices shared the effect of enhancing gamma power in the parieto-occipital area.

Study on Pain reduction through mediation

This research experiment (Zgierska et al, 2016) was used to examine the correlation between mindful meditation on the chronic lower back pain syndrome(CLBP). CLBP is a frequently occurring, disabling disorder developed from the work situation our society is forced to exist in today. It is often treated by opiate drugs, which have a reputation to be controversial due to the side effects they can cause.

The basis of the study (Zgierska et al, 2016) was to reveal that the mindful meditation can lead to a reduction in pain caused by the CLBP. The study involved a 2 hour 8 week group sessions of mindful meditation, and an at home practice of 30 minutes a day 6 days per week, where the participants had no prior experience with the practice. The participants used, had sensation in both of their hands in order to measure pain sensitivity. The pain was measured at baseline (8 weeks), then at the final week 26. The pain intensity was measured through “the four-item pain severity subscale from the validated Brief Pain Inventory” that provides information about the current and prior week worst, average, and least pain based upon the Numerical Rating Scale (which is an 11 point pain severity scale proving reliable for CLBP). To add also the physical function (disability) was recorded through the Oswestry Disability Index (ODI), which is a 10 point scale. The physiological state of the participants to pain was measured using the 20-item Chronic Pain Acceptance Questionnaire (CPAQ), a higher score with better acceptance of pain. Participants on average lower back pain for 14.210.1 years and were treated with opioid therapy for 7.95.7 years.

The results showed that at baseline (8 weeks) on average the participants showed pain of 5.81.4 points. The control group were exposed to a lower average intensity of pain at 4.9 while the mindful meditation group being 6.3. The control group showed a 52.6 average pain acceptance compared to the higher 56.2 pain acceptance for the mindful meditation group. The later group also received a higher perceived average stress (22.6 compared to 16.4). From the results of the experiment it proposes that mindful meditation can provide an outlet to reduce pain and stress in CLBP disorder, this suggesting that for the larger scheme of pain and stress and that mindful meditation could be a possible outlet.

State and Training Effects of Mindfulness Meditation on Brain Networks Reflect Neuronal Mechanisms of its Antidepressant Effect

The research study (Yang et al, 2016) shows the neuronal mechanisms behind the antidepressant effects of mindfulness meditation. The subjects used to carry out this experiment were 13 native spanish speaking university students, with no prior meditation experience. They were recruited to participate in a 40 day mindfulness meditation course. All of the subjects/participants were screened for psychiatric or neurological conditions prior to partaking in the study. The research was based upon a longitudinal design assessing the changes in functional magnetic resonance imaging, or fMRI, before and after 40 days of mindfulness meditation training in 13 novices. Relying on the coupling of cerebral blood flow and neuronal activity, fMRI detects specific areas of activity due to increased cerebral blood flow. The training consisted of 8-week courses, with daily practice at home involving 45 minute meditation sessions. The mindfulness based stress reduction (MBSR) programme was a series of 8, 1.5hr sessions over the course of 8 weeks.

Using a 1.5 T Siemens AVANTO scanner, the subjects were scanned twice, once before the training began - a single resting state (RS) scan, and then after the 40 days, the participants were scanned twice again; an RS scan as well as a scan during their meditation practice (MS).

The subjects completed three self-assessment questionnaires both before and after the study and POMS (Profile of Mood States) assessments throughout the study which measures: anger, fatigue, tension, depression, vigor and friendless. In addition, the Center for Epidemiologic Studies Depression Scale was used to measure improvements of depression-like symptoms before and after the study was completed.

The researchers focused on a specific, related area of the brain to measure the effects of mindfulness meditation; the Default Mode Network (DMN). This was chosen based on the decision to monitor the effects of mindful meditation practice on the neuronal levels and antidepressive changes on the activation pattern of the DMN. The DMN includes the following areas of the brain: medial posterior cortex - posterior cingulate cortex (areas 23/31), the precuneus, medial frontal cortex (areas 24/10-m/32) and the bilateral inferior parietal and posterior temporal areas surrounding the temporoparietal junction (TPJ). It is believed that the DMN has altered the resting state functional connectivity between networks when comparing depressed patients to healthy patients. Major Depressive Disorder patients exhibit more neural functional connectivity between the posterior cingulate cortex and the subgenual-cingulate cortex during resting periods.

The study found that there was a significant difference in functional connectivity when resting versus meditating. The ICA1 showed that during mindful meditation the Default Method Network (DMN) had stronger association of the temporoparietal junction and precuneus compared to when the subjects were in the resting scan stage. Whereas the activity within the frontal, cingulate and insular cortex was less associated with the Default Method Network. This finding may be inferred as the expected ‘network dissociation’ as a function of cognitive task during meditation. Additionally, significant decrease in anxiety/depression scores were recorded. The CES-D control score for depression is >16. Initially the subjects started with an average score of 16.23 and after training the average score was 9. With these results of the CES-D (Center for Epidemiologic Studies Depression Scale) scores, it can be believed that consistent practice of mindful meditation can lower by approximately 50% the symptoms of depression. Furthermore, subjects reported that short term meditation lowered acute feelings of tension at the time of scanning.

Reviewing the self-reports of the participants throughout the study as well as the recorded data, the results describe that with continuous practice and exercising the act of mindfulness during meditation, the subjects moods and outlook improved. This supports that mindfulness meditation can be therapeutic by inducing related network changes, altering the neuronal basis of affective disorders such as depression.

1The “Independent Component Analysis (ICA) which is a test that does not rely on a priori model of brain activity, parcellation of regions of interest or choice of seed regions but has been widely used to detect resting state networks was used as the complementary data-driven approach” (Yang et al, 2016).

Conclusion

Meditation can allow use to train our attention processes. We also learned how different meditation practices can vary in brain frequencies but on average they share the effect of enhancing gamma power in the parieto-occipital area. Meditation used in people have been shown to experience less pain in certain disorders. Mindful meditation has also shown enlargement of the volume in certain brain areas. Overall we can see from the research studies that mediation has many beneficial correlations with how the brain interacts with our environment. With the practice of consistent and long-term meditation, the effects have shown to positively influence neuronal activity, decreasing depression-related symptoms supported by the activity of the temporoparietal junction and it’s connection with the anterior cingulate cortex.

Meditation has shown positive benefits on physical health and stress reduction but recently it has shown positive effects on the brain by neuroimaging. There is proof that the brain structure has been to be altered by meditation.

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Internet Sourced research

Orbitofrontal cortex wikipedia page: (for the figure 1): https://en.wikipedia.org/wiki/Orbitofrontal_cortex#/media/File:MRI_of_orbitofrontal_cortex.jpg

Date accessed: May, 4, 2019 (Free to use indicated on website)

Hypothalamus wikipedia page: (for figure 2): https://en.wikipedia.org/wiki/Hypothalamus#/media/File:1806_The_Hypothalamus-Pituitary_Complex.jpg

Date accessed: May, 4, 2019 (Free for use indicated on website)