Mindfulness and meditative practices can be identified as a group of complex cognitive processes aimed at altering one’s sensory perceptions, emotions, autonomic nervous system and attention. Meditation has traditionally been used by religious (e.g. Buddhist) individuals
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seeking insight or transcendence by dissolving their sense of self and becoming aware of their surroundings. Today meditation is also beginning to be widely used in medical settings to treat a range of physical and mental disorders such as chronic stress. Since meditation affects many different aspects of the brain and body it is extremely difficult to pinpoint a precise mechanism by which it operates however, with recent
advancements in neuroimaging techniques, there is now a better idea of how meditation might operate on a neurobiological level.[1]
Research in the field of meditation has been known for small sample sizes, absence of proper control conditions, and an overall lack of experimental rigor however that has been changing in recent years due to theoretical and methodological advancements in the field.[2]

Contents

1 General Working Model of Meditation
2 Neural Basis of Meditation
3 Effects
4 Medical Applications

General Working Model of Meditation


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Schematic representation of a possible neurophysiological mechanism of meditative states. see reference #1
Mindfulness practices have been used for centuries however only recently have scientists begun to take notice of the physiological importance of such practices. Since meditation affects such a wide array of bodily functions, it has been very difficult to pinpoint an exact mechanism by which it operates. Recent advancements in the neuroscience field, namely improved neuroimaging techniques, have allowed scientists to create well integrated hypothesis based on empirical evidence gathered from a wide range of neuroimaging studies.[3] [4]
A schematic representation of one such integrative model can be seen to the right.
There have been a number of suggested models for meditation; some as recently as the month of this entry's writing.[5] However all models appear to implicate the highly important prefrontal cortex due to its vital importance in attentional processes as well as medial temporal lobe structures such as the hippocampus and enthorhinal cortex. The convergence of multiple models on specific brain regions of interest suggests that scientists have a good basic understanding of the cognitive mechanisms involved.

Neural Basis of Meditation

It is clear from looking at recent models that meditation uses both sympathetic and parasympathetic pathways, uses both excitatory glutaminergic as well as inhibitory gabaergic signals, and affects a wide range of cortical and subcortical brain regions bilaterally including: prefrontal cortex, cingulate cortex, thalamus, posterior superior parietal lobule, hippocampus, parahippocampal cortex, hypothalamus, and a number of endocrine glands.
Though there have been a number of models throughout the years, only the account by Newberg and Iversen (2003) seems to try and not only pinpoint the neurological substrates of meditation, but to also discuss the physiological effects these neurological changes cause.[6]


Prefrontal and Cingulate Cortex

The prefrontal cortex is the most sophisticated area of the neocortex. Studies have long indicated the involvement of the prefrontal cortex in delegating attentional resources.[7] [8] It is not surprising then that any neurological account of meditation should start in the prefrontal cortex as meditation is largely the practice of training and turning one's attention inwards. In addition to attention, the prefrontal cortex has been implicated in orchestrating complex cognitive functions such as working memory, executive control and even moral judgement. Studies have indicated increased blood flow in the prefrontal cortex region for over a decade now. These early studies used positron emission topography (PET) techniques to show increased cerebral blood flow to the prefrontal and cingulate cortices.[9] [10] More recent imaging studies have continued to show similar results now using more advanced neuroimaging techniques such as functional magnetic resonance imaging (fMRI) in addition to the temporally sensitive EEG's. One such study found increased activation in the anterior prefrontal cortex even in novice meditators and has implicated serotonin (5-HT) as an important neurotransmitter in meditation.[11]

Thalamus

The thalamus is an important structure located between the cerebral cortex and the midbrain. The thalamus functions as a relay of sorts for information flow throughout the brain, it relays sensory and motor information to and from the cerebral cortex. As such, the thalamus has been implicated in processes vital for mindfulness practices, e.g., consciousness, attention. It has been suggested that during mindfulness practices the increased activity in the PFC would cause a concurrent increase in thalamic activity, namely in the reticular nucleus, which secretes the inhibitory c-aminobutyric acid (GABA) neurotransmitter onto the lateral posterior and geniculate nuclei which in turn would decrease sensory input into the posterior superior parietal lobule thereby creating a feedback loop to focus attention.[12] This hypothesis is further supported with evidence from a recent study which compared yoga (a form of mindfulness practice) practitioners with a control group.[13] This study found a 27% increase in brain GABA levels in the yoga over the control group. Furthermore another study has suggested that the thalamus is also involved in the pain modulating effect found in mindfulness practitioners where reduction in pain was associated with thalamic deactivation.[14]
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Posterior Superior Parietal Lobule

The posterior superior parietal lobule (PSPL) is the smallest area of the brain discussed in this current article and thus it is important to get a sense of where exactly in the brain it is located. The PSPL is located in the parietal lobe along the mid line of the brain and is located just above the intraparietal sulcus (see illustration on the right). This area has long been associated with visuospatial processing. The PSPL integrates various sensory inputs to aid in the construction of a rich three dimensional representation of the body's position in space which in turn allows for coordinated motion as well as controlled interactions with one's environment. As previously mentioned, the PSPL receives inputs from the thalamus and is therefore a part of the widespread attentional network that was being discussed. Recently it has also been suggested that the PSPL plays a major role in working memory manipulation.[15] In this experiment researchers tested individuals with lesions to the superior parietal lobule and found that damage to this area was reliably correlated with deficits on memory tests requiring informational manipulation but not ones requiring simple rehearsal processes or long term memory. These finding illustrate the the superior parietal sulcus is vital for informational manipulation in working memory.
It has been shown that during meditation there is decreased activation of the PSPL.[16] The involvement of the PSPL in the positioning of the body in three dimensional space has led researchers to postulate that the deactivation of the PSPL during meditation via a gabaergic pathway leading from the thalamus would lead to the dissolution of the self concept and a feeling of being connected to one's surroundings which is often reported by practitioners of mindfulness practices.[17]

Medial Temporal Lobe

The medial temporal lobe (MTL) is actually a collection of many smaller structures such as the hippocampus, perihippocampal cortex, amygdala and many other structures. The importance of the medial temporal lobe has been known for a very long time. Much of the currently available research on the medial temporal lobe is centered around memory which the MTL is famous for. The limbic system is extremely important in mindfulness practices because activation of this system has been associated with reports similar to those experienced during meditation.
The hippocampus is a structure found in the MTL which is most commonly associated with memory research but it is also a crucial component of the attentional network. The hippocampus has a variety of projections throughout the brain and importantly interacts with the prefrontal cortex. The hippocampus can recieve stimulation from the thalamus via the glutamenergic pathway which would in turn feedback onto the prefrontal cortex through the nucleus accumbens and the neurotransmitter dopamine. It has been suggested that there is also reciprocal feedback from the hippocampus onto the amygdala which explains the emotional changes experienced during meditation.[18]

Hypothalamic Relay

The hypothalamus is a brain structure composed of many smaller nuclei which are responsible for regulating the body's homeostasis. The effects of mindfulness practices on the hypothalamic relay is what causes the widespread changes and the evident physiological response through a number of hormones and neurotransmitters. The limbic system is extremely interconnected with the hypothalamus and indeed stimulation of the right lateral amygdala leads to increased activity in the ventromedial hypothalamus which in turn leads to the activation of the parasympathetic nervous system.[19]

Effects


This article has demonstrated that the number of neurological substrates affected by mindfulness practices is vast. It is no surprise then that mindfulness practices have extremely wide spread effects throughout the rest of the body.
As previously mentioned, mindfulness practices affect systems involving attention, emotion, and the autonomic nervous system. In addition to these, the effects

Attention

One of the main effects of mindfulness practices is that on the attentional system. This paper has attempted to illustrate the pathway and effects that mindfulness practices have on attention through the various neural pathways previously described. Researchers have concluded that mindfulness allows people to more aptly control their attentional machinery, allowing for shifting of focus.[20] These enhanced regulatory abilities could then in turn enhance a person's ability of a variety of cognitive tasks such as insight problem solving and even improving working memory capacity.

Emotions

As previously mentioned, mindfulness practices affect emotions through the amygdala and the hypothalamic regulation of bodily hormones. It has been suggested that due to the secretion of serotonin found during mindfulness practices helps improve mood.[21] This is not surprising as this is exactly the way that anti depression drugs such as selective serotonin reuptake inhibitors work; by increasing the availability of synaptic serotonin. Furthermore, it has also been shown that the practice of meditation actually changes the way sadness is expressed.[22] This research has shown that through meditation, the recruitment of somatosensory cortical areas can be reduced which correlates to lower vulnerability to dysphoric feelings.

Autonomic Nervous System

Finally, mindfulness practices have great effects on the autonomic nervous system. As mentioned above, the parasympathetic system is activated during mindfulness practices through the hypothalamus. Activation of the parasympathetic system leads to many desired bodily effects such as decrease in respiration rate, decrease in heart rate and an overall decrease in stress hormone levels. Overall, just as with attention, research suggests that mindfulness practices grant people greater control over their autonomic nervous systems.[23]

Medical Applications

Having discussed many of the effects that mindfulness practices have on the body, it should be clear that mindfulness practices pose a great potential alternative avenue for treatment of various disorders. Research shows that mindfulness based stress reduction clinical practices which seeks to alleviate suffering through increasing an individual's awareness of moment to moment experiences and the associated mental processes has shown a consistent effect size of 0.5.[24] This suggests that mindfulness based treatments could be effectively used to treat a large number of both physiological and psychological ailments including chronic stress disorders, panic disorders, anxiety disorders, depression, emotional dysregulation and many more. It is encouraging to see research being done into this promising non-invasive set of techniques.


  1. ^ Newberg, A. B., & Iversen, J. (2003). The neural basis of the complex mental task of meditation: Neurotransmitter and neurochemical considerations. Medical Hypotheses, 61(2), 282-291. doi:10.1016/S0306-9877(03)00175-0
  2. ^ Lutz, A., Slagter, H. A., Dunne, J. D., & Davidson, R. J. (2008). Attention regulation and monitoring in meditation. Trends in Cognitive Sciences, 12(4), 163-169.
  3. ^ see [1]
  4. ^ see [4]
  5. ^ Sperduti, M., Martinelli, P., & Piolino, P. (2012). A neurocognitive model of meditation based on activation likelihood estimation (ALE) meta-analysis. Consciousness and Cognition, 21(1), 269-276.
  6. ^ see [1]
  7. ^ Rossi, A., Pessoa, L., Desimone, R., & Ungerleider, L. (2009). The prefrontal cortex and the executive control of attention.Experimental Brain Research, 192(3), 489-497. doi:10.1007/s00221-008-1642-z
  8. ^ Asplund, C. L., Todd, J. J., Snyder, A. P., & Marois, R. (2010). A central role for the lateral prefrontal cortex in goal-directed and stimulus-driven attention. Nature Neuroscience, 13(4), 507-512.
  9. ^ Newberg A. B., Alavi A., Baime M. et al. (2001). The measurement of regional cerebral blood flow during the complex cognitive task of meditation: a preliminary SPECT study. Psychiatry Research: Neuroimaging 106, 113–122.
  10. ^ Lazar S. W., Bush G., Gollub R. L. et al. (2000). Functional brain mapping of the relaxation response and meditation. Neuroreport. 11, 1581–1585.
  11. ^ Yu, X., Fumoto, M., Nakatani, Y., Sekiyama, T., Kikuchi, H., Seki, Y., . . . Arita, H. (2011). Activation of the anterior prefrontal cortex and serotonergic system is associated with improvements in mood and EEG changes induced by zen meditation practice in novices. International Journal of Psychophysiology, 80(2), 103-111.
  12. ^ see [1]
  13. ^ Chris C. Streeter, J. Eric Jensen, Ruth M. Perlmutter, Howard J. Cabral, Hua Tian, Devin B. Terhune, Domenic A. Ciraulo, and Perry F. Renshaw. (2007). Yoga Asana Sessions Increase Brain GABA Levels: A Pilot Study. The Journal of Alternative and Complementary Medicine. 13(4): 419-426. doi:10.1089/acm.2007.6338.
  14. ^ Salomons, T.,Aaron, K. (2011). Does Meditation Reduce Pain through a Unique Neural Mechanism? The Journal of Neuroscience, 31(36), 12705-12707;doi:10.1523/JNEUROSCI.2843-11.2011

  15. ^ Koenigs, M., Barbey, A. K., Postle, B. R., Grafman, J. (2009). Superior parietal cortex is critical for the manipulation of information in working memory. The Journal of Neuroscience, 29(47), 14980-14986; doi: 10.1523/​JNEUROSCI.3706-09.2009
  16. ^ Wang, D. J. J., Rao, H., Korczykowski, M., Wintering, N., Pluta, J., Khalsa, D. S., & Newberg, A. B. (2011). Cerebral blood flow changes associated with different meditation practices and perceived depth of meditation. Psychiatry Research: Neuroimaging, 191(1), 60-67. doi:10.1016/j.pscychresns.2010.09.011
  17. ^ see [1]
  18. ^ see [1]
  19. ^ Davis, 1992 as cited in Newberg & Iversen, 2003
  20. ^ Lutz, A., Slagter, H. A., Dunne, J. D., & Davidson, R. J. (2008). Attention regulation and monitoring in meditation. Trends in Cognitive Sciences, 12(4), 163-169.
  21. ^ see [1]
  22. ^ Farb, N. A. S., Anderson, A. K., Mayberg, H., Bean, J., McKeon, D., & Segal, Z. V. (2010). Minding one's emotions: Mindfulness training alters the neural expression of sadness. Emotion, 10(1), 25-33a. doi:10.1037/a0017151
  23. ^ Tang, Y., Ma, Y., Fan, Y., Feng, H., Wang, J., Feng, S., . . . Fan, M. (2009). Central and autonomic nervous system interaction is altered by short-term meditation. Proceedings of the National Academy of Sciences, 106(22), 8865-8870. doi:10.1073/pnas.0904031106
  24. ^ Grossman, P., Niemann, L., Schmidt, S., & Walach, H. (2004). Mindfulness-based stress reduction and health benefits: A meta-analysis. Journal of Psychosomatic Research, 57(1), 35-43.