Abstract

The search for understanding the nature of human consciousness and our true identity has been a central theme throughout history. Meditation has emerged as a crucial practice in this pursuit, with yoga being one of the most extensive and ancient systems of meditation techniques. These techniques include practices such as focused attention, mantra recitation, and open monitoring. This review explores the neurophysiological changes associated with different meditation techniques, noting that the activation and deactivation patterns in the brain differ across techniques, highlighting the common structures in all of them and the variations on each one. The findings suggest that meditation practices can enhance neural connections, improve cognitive functions, attention, regulate emotions… It is interesting to know that there are different benefits depending on the type of meditation practiced, in order to address it in clinical practice.

Keywords: Meditation; Focused Attention; Mantra Recitation; Open Monitoring; Loving-Kindness and Compassion; Neuroanatomy; Neurophysiology

Introduction

If there is a mystery that has intrigued humankind throughout history, it is the discovery of our true identity. The question of who we are and what the purpose of our consciousness is has resonated, hidden in our minds in different ways, as we carry out our daily tasks. Some have attempted to unravel this question through active mental processes, developing intricate and diverse philosophical theories that are difficult to corroborate. In contrast, a significant number of wise individuals with notable self-realization, throughout history and across all cultures, have gifted us some of the principles necessary to achieve this goal [1]. The common thread that all of them agree on is the importance of mental stillness; only by quieting that internal dialogue to which we are sometimes subjected can we not only learn to master it but also access a purer part of our being and essence. This essence or being represents an aspect of ourselves that some call super consciousness, others the higher self, or even the soul-a part that, the more access you have to it, the more knowledge and good quality of life you can acquire. This is how we begin to refer to the process of meditation, discovering the multitude of qualities that a technique as seemingly simple as physical and mental silence can provide [2].

From here, countless branches and techniques with distinct nuances emerge. A traditional discipline, perhaps the oldest and most extensive regarding meditation techniques that has reached the present day, is yoga. Since the Vedic texts of the 15^th century BCE, it has developed as seen in the "Yoga Sutras" of Patanjali in the 5^th century BCE [3], passing through other great yogis, each offering their own perspective and school, although all are similar and agree on the essentials. Within the various meditation techniques, several are distinguished, such as concentration on a point (samatha), observation without identification (prajna), control of breathing (pranayama), and others following increasingly complex and elaborate processes (pratyahara, dharana, dhyana…) [4]. From the beginning of practice, one can already experience initial results such as physical relaxation, decreased breathing cycles and heart rate [5]. From there, depending on perseverance and seriousness in practice, one can undergo a multitude of beneficial changes in life, culminating in a final goal that great sages claim can be achieved, such as samadhi or enlightenment. This would be the ultimate realization of being, the very etymological purpose of the word Yoga, which signifies the union with our divine essence or spirit [6].

Discussion

For all these reasons, interest in studying meditation through scientific methods has increased in recent years to verify its effects, demonstrating that new and beneficial aspects are continually being discovered, opening a vast array of nuances yet to be explored [7]. There are three distinct periods in research: a first period focused on its therapeutic effects, distinguishing novice meditators from experts and providing the first studies on brain activity; a second period aimed at relating cognitive-affective mechanisms to health benefits; and a third phase, the current one, in which neurophysiological and anatomical findings and studies centered on advanced meditations are analyzed [8]. In this mini-review, we delve into the knowledge of neuroanatomy and the reactions that occur at the level of the central nervous system during various meditations [9]. Certain brain areas are generally recruited across multiple techniques [10], primarily the insular cortex at different levels, which, although related to numerous functions, mainly involves interoception (including breathing and heart rate) [11], metacognition [12], and empathy [13]. Less commonly, the premotor and supplementary cortices are involved in the execution and voluntary planning of movements, memory, attention control, and reasoning [14,15].

Based on the 2016 review and meta-analysis by Fox KCR, et al. of 78 functional neuroimaging studies, the activation/deactivation of different complementary brain structures is described depending on the specific meditation techniques [10]:

Meditation Based on Focused Attention: This is the most studied technique and consists of bringing attention to a specific focus and redirecting it back again to that if the mind wanders, often focusing on breathing.

Activation of the dorsolateral prefrontal cortex and left medial insula, linked to attention to breathing [11]; also, the dorsal anterior cingulate cortex associated with the regulation of emotions and attention [15]. Deactivation of ventral posterior posterior cingulate cortex and left inferior parietal lobe, responsible for episodic memory and conceptual processing [16]. This can help reduce spontaneous thoughts of the past and future, providing mental calm.

Mantra Recitation: This consists of the repetition of a sound, word or prayer as a tool for concentration.

Activation of the basal ganglia, globus pallidus and putamen for the ‘reward’ system, performance of highly trained movements, generation of habits, can help inhibit undesired movements, generating smoothness of movement [17]; which can be useful in people with motor disorders. Broca's area, where speech motor skills are generated. Fusiform, corneal and precuneus gyrus, involved in visual information and motor imagery. Deactivation anterior insula, thalamus, somatosensory and interoceptive cortex and inferior parietal lobe, which are responsible for processing somatosensory and interoceptive information [18], which may help to focus on meditative activity by decreasing awareness of these afferents, including auditory ones.

Open Monitoring (Prajna): Prajna is the observation of mental content without involvement or judgement.

Activation medial and anterior insula, referring to viscerosomatic information and thus improving the integrative function of the organism's internal and external information [19]. It shares activation of the dorsal anterior cingulate cortex with focused attention meditation, both of which can improve attention and emotion regulation. Deactivation pulvinar thalamus, inhibiting visuospatial attention [20], which may be related to the ‘non-involvement’ premise required by the technique itself.

Loving-Kindness And Compassion: Consists of creating feelings of empathy and love, initiating the practice individually and extending it to all beings.

Activation Anterior insula, parietooccipital sulcus, somatosensory cortex and inferior parietal lobe favouring awareness of bodily sensations and feelings, also linked to the virtue of greater empathy [21]. No significant deactivations.

Challenges and Considerations

It would provide more information to continue this line of research by generating studies that are as homogeneous and replicable as possible. It would also be interesting to increase the number of studies in the categories that are less treated. On the other hand, it could provide broader information on how meditation affects by performing neurofunctional tests not only during, but also in a basal and subsequent state, thus considering the different variables of the structural idiosyncrasies of each subject, as well as the recording of habits and lifestyles. And, for completeness, certain cortical activations mentioned could be refuted by standardized tests, such as those related to motor control or balance in different populations and health situations.

Conclusion

This review suggests that meditation can provide beneficial neural connections, with the most frequent effects being improved attention, cognitive functions and emotional control. However, the practice of different meditation modalities may have different effects. Knowledge of the structures involved in the different types of meditation may be helpful in approaching clinical practice.

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