The human brain is about the size of a cantaloupe, weighs about 3 lb, and has average length, width, and height of 17 cm (6.75 in.), 14 cm (5.5 in.), and 9 cm (3.5), respectively. The human brain has 100 billion nerve cells (called neurons). When we add other supporting cells in the brain, this number becomes 1.1 trillion cells (1 trillion = 10¹²). Although the brain weighs only 2 % of the body’s weight, it consumes approximately 20 % of the body’s supply of oxygen and glucose. The largest section of the brain is the cerebrum, which constitutes 85 % of the brain’s weight. The outer part of the cerebrum is the cortex. The cortex is the thinking apparatus. The inner part of the cerebrum is divided into subcortical structures, including the limbic lobe and basal ganglia, which largely govern feelings and unconscious processes. The human cerebrum is divided into two hemispheres: the left and the right. These hemispheres communicate with each other via the corpus callosum, which consists of some 250 million nerve fibers. Nerve fibers are the thin threadlike structures that transmit nerve signals from the nerves to receptors located in various parts of the body. Each hemisphere can be further divided into four lobes: the frontal (the front of the brain), parietal (the middle and top of the brain), temporal (the middle and bottom of the brain), and occipital (at the back) lobes. Some researchers (Kosslyn and Miller 2013) also propose a functional division of the human forebrain into the top brain and bottom brain. This division is demarcated largely by a groove that separates the frontal and parietal lobes from the temporal lobe below. This groove is referred to as the Sylvian fissure or lateral sulcus (detailed descriptions are provided later in this chapter). The section of the cerebrum that distinguishes humans from other primates is the frontal lobe, more specifically the prefrontal cortex (PFC). The PFC is the bulging portion of the frontal lobe that sits behind the forehead and above the brow. The upper and outer part of the PFC (referred to as the dorsolateral PFC or DLPFC) oversees critical human faculties such as problem solving, organization, maintaining a flexible attitude, and planning for the future. It is not surprising then that the PFC constitutes 30 % of the human’s cortical volume. The frontal lobe is the thinking center of the brain, whereas the limbic areas are the feeling centers of the brain.

Hanging below the cerebrum is the brain stem, which is popularly referred to as the reptilian brain because of its involvement in various bodily reflexes. The brain stem consists of three structures: the midbrain, pons, and medulla. These three structures primarily regulate the body’s vital functions like breathing, heartbeat, and body temperature. From evolutionary perspective, the oldest part of the human brain is the brain stem and the limbic lobe (limbus means a ring). The limbic lobe, the feeling part of the brain, lays buried deep inside the brain and surrounds the most vital centers contained in the brain stem, the breathing and heart centers. One particular region within the temporal lobe is the insula. This is a portion of the cerebral cortex folded deep within the lateral sulcus that separates the temporal lobe from the parietal and frontal lobes. The insula is responsible for storing and registering the visceral emotional representations of our experiences. Functional neuroimaging studies have found that the insula is activated when the individual imagines experiencing pain in response to images of painful events. The insula also plays a crucial role in interoceptive information processing. The insula links our internal experience of bodily functions like heartbeat to evaluative information, thereby generating a subjective representation of one’s own body. This includes a sense of body ownership, as well as social emotions like empathy (Karnath et al. 2005). The insula and the prefrontal cortex (PFC) play a critical role in the meditative experience. The brain communicates our thoughts and feelings to other parts of the body through mediation of a system called the autonomic nervous system: this system has two parts, the sympathetic (excitatory) system and the parasympathetic (calming) system. Within the brain, nerve cells are in constant communication with each other via connections (both physically and chemically) called synapses. On average, each nerve cell has approximately 5,000 connections to other nerve cells. There are two types of synapses: (1) electrical synapses where nerve cells are in physical contact with each other, and (2) chemical synapses, where communication is not transmitted through physical contact, but by the release of chemicals, referred to as neurotransmitters, at nerve endings. A typical nerve cell fires 5–50 times a second. When a nerve cells fires, it sends information signals to other nerve cells communicating whether or not it should fire too.

From an Eastern perspective, the connection between the mind and brain is well accepted. In fact, one of the foundational concepts among Eastern schools of thought is the integration of the mind and body. Tantra, tantric Buddhism (Vajrayana), and qigong propose elaborate energy systems throughout the human body. These various energy systems or flows are believed to support the underlying soul and human functions. These energy systems are called chakras in the Indo-Tibetan tantric system (as discussed in Chap. 1) and qu’ and yin–yang in the Chinese qigong system (Liang et al. 1997). Within these systems, mind–body dynamics are represented more holistically; mind–body interactions cocreate an experience. Our brain has tremendous inductive reasoning power such as the ability to infer complete patterns when perceiving just a small fraction of the pattern. For example, we can recall a person from just a few words or a whole concept from a single phrase. Even an advanced computer cannot match the inductive reasoning power of the human brain. (Further discussion regarding the role the brain plays in our experiences is provided later in this chapter.)

Most of us are more familiar with concepts of the left versus right brain. The science indicates that these concepts are oversimplifications. The structures of the brain do not operate independently but as a single interactive system that function in concert. Built upon decades of cognitive neuroscientific research on both the brains of rhesus monkeys and those of human beings, Kosslyn and Miller (2013), in their recent book, Top Brain, Bottom Brain, propose four different cognitive modes on the basis of how the top and bottom portions of their brains function. This mode is supported by the anatomical division of the top and bottom parts of the brain, demarcated largely by the Sylvian fissure. The top brain comprises the entire parietal lobe and the upper, larger portion of the frontal lobe. The bottom brain refers to the smaller remainder of the frontal lobe and the entirety of the occipital and temporal lobes. Kosslyn and Miller describe that the top–brain system uses information on the surrounding environment in determining what actions to execute and goals to achieve. This determination operates in a flexible and adaptable manner that varies with the particular needs of the circumstance.

The bottom–brain system, on the other hand, organizes signals brought to them from the sense organs and simultaneously compares these perceptions with all the information previously stored in one’s memory system. This set of comparative data is used to classify and interpret the object or event, allowing one to convey meaning to the world. While the top-brain system operates mostly on a here and now basis and in an executive or thinking-based mode, the bottom-brain system operates in a visceral, feeling, and meaning-based way. The major implication here is that the top- and bottom-brain systems always work together, albeit in varying extents that depend on the needs and personality of the individual. Kosslyn and Miller further elaborate that depending on the degree to which a person uses the top and bottom systems in various ways (cognitive modes), people can be categorized into four groups: movers, perceivers, stimulators, and adaptors. No one mode is better or worse than the others; rather, each mode contributes something useful. The key is how these cognitive modes interact—both among individuals and within groups of individuals that tend to favor one mode over another. If we can classify persons based on their brains, it must follow that the brain is an important locus for the experiences that shape the personality.

It is important to understand that consciousness in the yogic sense is different from that in the neurological sense. In the yogic sense, consciousness refers to the mind with its various grades or levels. These gradations are classified as the lower level (sensorial mind; Sanskrit manasa), the higher (the intellect; Sanskrit buddhi,), and, finally, the finest grade (the soul or pure experiential realm; Sanskrit atma). This understanding is essential to an understanding of the theories of the mind as described in yogic philosophies. Again we see that unlike the Cartesian perspective, Eastern traditions consider the human body in the context of a body–mind–beyond mind system. The beyond mind entity is the soul or the highest grade of the mind in its purest form. Aurobindo (1999, 2001), twentieth century philosopher, meditator, and proponent of the Integral Yoga, called this as beyond–mind entity or the supramental state. According to yogic philosophies, one’s insight into or knowledge regarding the various levels of Reality depends upon the grade of the mind under which we experience them. The various conditions or grades of the mind and their accompanying levels of knowledge provide us various representations or various levels of expression of the Reality. As described in classical Indian texts like the Yoga Sutras and the Visuddhimagga, meditation is nothing but the incremental process of purifying one’s mind, the interactive interface, until it achieves the highest, purest form (the soul or pure awareness). In this grade of consciousness, the meditator can see in the most vibrant and clearest way.

In the spirit of the body–mind–beyond mind conceptualization, all experience and existence lie within the spectrum of two poles. The somatic–cognitive pole, or the outer self, consists of the body and mind and includes our intellectual, conceptual knowledge regarding ourselves and the world. The other end of the spectrum is the experiential pole, the inner self, manifests within the context of our intuitional, nonconceptual knowledge regarding ourselves and the world. Experiential nature exists in the realm of the beyond mind. Some traditions refer to the inner self as the true self and the outer self as the false self or the projected self. The outer self depends more on the outer world, relying on feedback from the others. In contrast, the inner self is self-directed and thus depends more on the inner world, relying on introspective feedback. Unlike the inner self, the outer self seeks to impress others in order to receive positive feedback. Consequentially, when functioning in the realm of the outer self, one’s happiness is at mercy of others, and thus one experiences more stress and constraints.

In light of psychoanalytic thought, these two selves can be seen as the outer defensive structure and the inner core structure. Because the false self is a façade built on years of fearing retaliation and rejection by others, the individual is under more pressure. Maintenance of the false self requires a high cost, as it consumes all of the individual’s psychic energy. An example of this is the obsessive–compulsive person depleted of his/her psychic energy by maintaining psychological defenses against the experience of anxiety. This may explain why babies, despite their vulnerability and helplessness, appear happy and, furthermore, increase the happiness of others. The baby has simply not lived long enough to build a false self. The true self, on the other hand, is freer because it is more natural, unconditioned, and independent of the world. When one operates as the true self, it costs less. There is no need to expend the energy needed to maintain a façade; the surplus of psychic energy is free to fuel higher deeds such as creativity, altruism, and spirituality. Ancient descriptions of aura surrounding a spiritual person’s head are thought to be the result of this free psychic energy. Within the spectrum of outer self to inner self, spirituality is any factor or intervention that decreases the distance between the outer self and the inner self and promotes harmony between the two. In other words, spirituality is a sort of homecoming. The individual feels settled and, therefore, does not need to fabricate the projected false self. When practicing deeply contemplative methods like meditation, one experiences a process that gradually merges the outer self (i.e., the body and the lower mind) with the inner self (beyond mind or the soul) and, consequentially, the true experience. In order to understand spiritual experiences, we need a framework other than the one we ordinarily use to study non-spiritual experiences. In natural states like sleep or losing oneself in the vastness of nature, we can experience this merger in variable grades that depend upon the quality of the experience. The relaxing effects of sleep or vacationing can explain the stress-reducing effects of these mergers.

In both ancient and modern eras, Eastern philosophers (Buddhaghosha, 430 CE; Aurobindo 1999, 2001) have described the soul as the purest form or the finest grade of the mind or consciousness. In yogic philosophies, the consciousness and mind are often used interchangeably. These philosophies conceptualize the mind in terms of consciousness which is different from consciousness in neurological sense. This consciousness (mind is part of it) exists in graded form: from lower to higher and from crude to fine, and its finest grade is the soul which lies in the realm of direct or pure experience rather than mere intellect. The lower mind (Sanskrit manasa) is considered another sensory apparatus (Sanskrit indriya), just like the other five physical sense organs (touch, vision, smell, etc.). As long as one functions in the realm of the body and lower mind, one is functioning at an intellectual level that is inferior to deeper, experiential one. It is not surprising then that Yoga or meditation, as described in all the original traditions (the Vedas, the Upanishads, Shramana, and Tantra), begins with postures and breathing patterns that involve the gross body. The individual can then transcend the body through meditation and ascend into the subtler realm of the mind. In the Patanjalian tradition, practicing the various stages of samadhi allows one to access the indescribable or the Absolute, the finest or subtlest level of experience. Similar concepts in Buddhist traditions are called the jhanas and sampattis. They are the various access states of the mind as one ascends from the lower mind to higher mind and then beyond the mind.

As described earlier, the ancient Indian scriptural traditions (Upanishads and Visuddhimagga) claim that pure awareness or pure experience is the highest form of consciousness. This highest form has been referred to as soul or God or the Absolute. The body, mind/internal world, and the external world are merely derivatives of this Ultimate One. The highest yogic philosophies claim that both the mind and the physical body are gross material and external manifestations (Sanskrit jada) of that consciousness which is subtle and internal. The internal (i.e., the subtle consciousness or the soul) is the cause and the external (i.e., the gross body, mind, and world) is the effect. Consciousness is expanded energy (as described in Chap. 1, in tantric traditions, this energy is called the cosmic energy or kundalini energy [Sanskrit kundal = coil, spiral]). These concepts present profound psychosomatic implications regarding the body and mind and the intricate dynamics among them. Yoga’s rationale for the deep introspection lies in the fact that by taking control of the internal (the soul), one can also control the external.

Transpersonal psychology, a subdivision of Western psychology, integrates modern psychology with spiritual/meditative psychology. This school of psychology, as its name suggests, bridges (trans = across) the gap between conventional Western psychological schools and the contemplative philosophies of the East, both ancient (e.g., Buddhism) and modern (e.g., Sri Aurobindo’s Integral Yoga). Just as in modern psychology, in which the individual undergoes cognitive and emotional development that includes various stages, the prominent thinkers of the transpersonal movement (e.g., Ken Wilber, Jack Engler, D. T. Suzuki, and Mark Epstein) propose the developmental progression of spiritual development. This development is a multistage model of spiritual development that begins with the physical (gross) realms, followed by the mental (subtle) realms, and ends with the finest stage, the soul. Integrative models like this are not only helpful when studying Eastern philosophies from the perspective of Western psychology, but they also assist in the integration of the valuable insights of both schools. This integration allows for the understanding of a larger audience. For more descriptions, please refer to Wilber et al. (1986).

During information processing of the primate’s brain, one key process is pattern recognition, meaningful recognition of the different patterns of experiences across various domains of information. Pattern recognition forms a symbolic representation of an experience which maps it out on the brain. Although pattern recognition occurs in all sensory modalities, the visual pattern recognition in humans and other primates has been studied the most extensively (Haxby et al. 2001) and, thus, serves as a prototype. The process involves the following six steps in sequence: (1) transmission of the visual input to the occipital cortex; (2) routing the information to the lateral inferior occipital lobe, where a pre–pattern (an intelligent organization of the inputs) is developed; (3) the information is sent to the fusiform gyrus in the ventral temporal lobe, where it is categorized as one of two kinds—face or object; (4) from the fusiform gyrus, the data continue to be transmitted anteriorly: at the temporal pole, the object’s identity is further clarified and integrated with limbic information; (5) simultaneously, data regarding the object are transmitted to the parietal cortex, where the object is placed within three-dimensional space; and (6) the processed information regarding the object is sent to both the entorhinal cortex, where its past significance is determined, and the DLPFC, where its implications for the future are evaluated.

The significance of the human pattern recognition is that it processes all sources of information (i.e., visual, auditory, tactile, etc.) simultaneously. There are two types of interpretive processing: bottom–up (data driven or part-to-whole) and top-down (concept driven or whole-to-part). Information processing system in humans exhibits interaction between the data-driven and concept-driven processes. The arrival of sensory information triggers a series of automatic analyses, beginning with the sensory organs and subsequently through an extensive chain of processing stages. Simultaneously, the context in which the sensory events are embedded triggers expectations based upon past experience. Knowledge, in general, might be defined as expectations that produce concept-driven processing, top-down processes (the dorsal stream), which eventually merge with the bottom-up processes (the ventral stream). For the proper operation of the human information processing system, both the top-down and bottom-up processes must take place simultaneously, each assisting the other when one tries to make sense of the world. An example of this is the act of reading. Reading requires deciphering symbols (i.e., letters), consolidating them into units, and, finally, determining the word. Does one read by deciphering the letters and then constructing the words (bottom-up) or by interpreting the features of the entire word at once (top-down)? Reading is most likely a combination of both bottom-up and top-down processes, the balance of which is determined by what the situation demands. For example, when reading a difficult material, we probably use bottom-up processes. Evidence suggests that there exist multiple streams, some descending to the level of feature analysis, but reading requires quick feature analysis, giving way to a higher order of contextual recognition. This higher order follows that first reading the material engages letter recognition and quickly follows with whole word and phrase recognition (Mather and Wendling 2012). Unfamiliar material is interpreted on the level of morphemes, the smallest grammatical units, while practiced readers tend to maintain the holistic analysis. Reading studies have led to another remarkable discovery: a single printed letter is sometimes read better when it is part of a word than when it stands alone (Wheeler 1970). This author integrates these insights with techniques of mindfulness in his mindfulness-based trataka model (MB-t^©, Pradhan 2014) which he uses for the treatment of dyslexia. Trataka is a concentrative meditation (focused attention type) practice of which improves the visual memory (Niranjananada 1993).

Considering the complexity of human experience, any attempt to fully describe the experience in terms of neural circuitry would be an oversimplification. Placing ancient wisdom of yogic and meditative philosophies within the framework of modern science and evidence-based medicine could lead to a better understanding of both disciplines, more synergy, and enhancement of their therapeutic potential. With this in mind, the five major neural circuits that play a critical role in the neural mapping of our experiences are as follows:

The three circuits in the PFC that modulate our complex behavior are located in three chief regions: the dorsolateral prefrontal cortex (DLPFC), the anterior cingulate cortex (ACC), and the orbitofrontal cortex (OFC). These areas are somatotopically mapped and characterized by numerous pathways or channels that run through each region (Mega and Cummings 2001). It is interesting to note that similar descriptions of energy channels (Sanskrit nadis) of the human body are detailed in the ancient Indian Tantric texts (Avalon 1974; Sivananda 1994). The DLPFC is a neural workspace where information needed to evaluate situations, make decisions, solve problems, and plan for the future is gathered. DLPFC constitutes the thinking brain and tends to participate in cognitive circuits, whereas ventral prefrontal areas comprise the feeling brain, as they are significantly linked to emotional circuitry.

The circuit in the anterior cingulate cortex (ACC) is involved primarily in the motivation of goal-directed actions, processing of emotions and the emotion-associated movements, emotional–cognitive integration, and conflict monitoring (Bush et al. 2000). Anytime we consciously exercise our will, we activate our ACC. It transmits emotional motivation to the autonomic, visceromotor, and endocrine systems (Critchley et al. 2003). Because the ACC is central to deliberate and reasoned motivation, it is an important component of reward circuitry. The ACC is not only strategically sandwiched between but also connected by the DLPFC, associated with attention and executive functions, and the OFC, the area that elicits risk evaluation and impulse control. The ACC is closely connected with the DLPFC, which gathers information needed for problem solving, and also with the supplementary motor area of the frontal lobe, the region responsible for planning novel movements. These strategic locations and connections assist the cingulate in receiving cognitive data from the DLPFC (Barbas et al. 2003); facilitate emotional–cognitive integration, generating emotional states appropriate to cognitive contents (Critchley et al. 2003); and convey emotional information to the DLPFC for further cognitive processing. In response to cognitive information, the dorsal ACC triggers the arousal responses of autonomic centers (Critchley et al. 2003).

The ACC is the primary overseer of our attention. It is also the chief neural region associated with the manifestation of targeted and purposeful fulfillment of our actions. It manages our effortful control over various things. It is significant that the ACC works closely with the amygdala, the center for fear learning, which is also associated with motivation. Together, the ACC and the amygdala form a joint system that elicit two forms of motivation: the ACC controls top-down, deliberate, centralized, and reasoned motivation (cool motivation), whereas the amygdala is responsible for bottom-up, reactive, distributed, passionate motivation (warm motivation) (Hanson and Mendius 2009). The ACC and the amygdala modulate each other: in a three-step feedback loop, the amygdala excites the lower part of the ACC, which then excites the upper part of the ACC, which in turn inhibits the amygdala (Lewis and Todd 2007). The other inhibitor of the amygdalar activity is the ventromedial prefrontal cortex (vmPFC). The vmPFC is the mentalizing region of the brain (further described in Chap. 6), and the nerve fibers that arise from it directly inhibit the firing of the amygdala in situations of fear or anxiety. Given its functions, damage to the ACC may result in a lack of motivation and a general state of apathy, in which responses to internal and external stimuli are diminished. Severe damage to the ACC can result in akinetic mutism, a state characterized by little spontaneous movement or speech (Mega and Cummings 2001). Because of its role in reward and motivation, ACC–nucleus accumbens circuitry plays a significant role in addiction. The ACC is not fully developed until 3–6 years of age (Posner and Rothbart 2000), which explains why young children demonstrate less self-control. Around 7 years of age, the child develops the level of cerebral, cognitive, and emotional maturation necessary for meaningful participation in attentional activities like those of meditation.

The third player in the tri-circuit is the orbitofrontal cortex (OFC) which primarily functions to control one’s impulses and promote the pursuit of low-risk rewards that are consistent with one’s internal needs over high-risk ones. The OFC circuit modulates our pursuit of reward within the context of careful considerations of potential consequences. As a result of its connections with the ACC and the autonomic nervous system, the OFC induces anticipatory bodily states that encourage reward seeking, as well as aversive bodily states that reduce the likelihood of risky behavior (Mega and Cummings 2001). From an evolutionary perspective, the OFC modulates behaviors that have significant bearings on the individual’s survival.

The orbitofrontal cortex (OFC) includes distinct medial and lateral areas as well as dorsal and ventral areas (Elliott et al. 2000; Kringelbach 2005). The medial orbitofrontal cortex is active in monitoring associations between stimuli, responses, and outcomes under changing circumstances, whereas the lateral orbitofrontal cortex is active in inhibiting previously rewarded actions that are no longer likely to be rewarded owing to changed conditions. Exhibiting strong links to the thalamus (the sensory relay station), the ACC (the center for conscious motivation and attention), and the autonomic nervous system, which is responsible for fright–fight–flight response, the amygdala rates the emotional importance of any experience. When we reappraise a situation according to the negative and positive emotions associated with our previous memory of it, we activate corresponding punishment and reward circuits: the orbitofrontal circuits for punishment and the ACC and basal ganglia circuits for the reward.

In the risk–reward evaluation circuits, the OFC and amygdala work together closely. The amygdala, the central alarm system, continuously monitors for opportunities and threats to the individual. The orbitofrontal cortex (OFC) is reciprocally connected to the amygdala; they act in concert to generate emotional states relevant to the pursuit of reward and avoidance of risk (Barbas et al. 2003: experimental work in nonhuman primates). Both the orbitofrontal cortex and the amygdala receive a significant input from all five sensory cortices, as well as from the insula, which again is associated with the visceral elements of our perceptions. The amygdala and OFC, by virtue of their connections to the hypothalamic autonomic centers and other particular subcortical targets, also generate emotional bodily states.

Our brain integrates all of these information into comprehensive and contextual views of external and internal stimuli, making sense of our outer and inner worlds. The amygdala can exert both inhibitory and stimulatory influences on hypothalamic autonomic nuclei. The central nucleus of the amygdala normally inhibits the hypothalamic nuclei, whereas the basolateral nucleus stimulates it. The OFC can suppress as well as activate the autonomic centers: the suppression happens through stimulation of the amygdala’s central nucleus, whereas activation happens through the intercalated cell masses of the amygdala. Stimulation of the autonomic centers occurs when the OFC stimulates the intercalated cell masses of the amygdala, thus diminishing the default inhibitory effect the central nucleus of the amygdala has on the hypothalamic nuclei (Barbas et al. 2003).

Both the OFC and amygdala work closely with the ventromedial prefrontal cortex (vmPFC) which plays a critical role in the evaluation of risk and fear and the suppression of emotional responses to negative emotional stimuli (Hansel and von Kanel 2008). The vmPFC does so by suppressing amygdalar activity and regulating the parasympathetic system. Not surprisingly, patients with vmPFC lesions show diminished emotional responsiveness and also markedly reduced social emotions like compassion, shame, and guilt. The OFC, amygdala, and vmPFC work together to integrate sensory input into comprehensive views of both the external and internal worlds. Imaging studies have shown that orbitofrontal and amygdalar circuits can be modulated through conscious cognitive processes (Ochsner et al. 2002). Deficits in the orbitofrontal–amygdalar circuit can present as impulsivity, social inappropriateness, lack of empathy, lack of respect for social conventions, disregard for rules and consequences, and little response to the threat of personal risk, embarrassment, or punishment (Mega and Cummings 2001).

The thalamus is a key midline structure of the brain that serves as a gate for all peripheral sensations, with the exception of smell, before these sensations are relayed to their final destination, the sensory cortex. The thalamus also plays an important role in the modulation of sensation, sleepiness and wakefulness, and one’s overall sense of awareness. The basal ganglia, on the other hand, lie at the base of the brain that play an important role in procedural learning and implicit memory, postures and movements, motivation and reward, habitual behavior, and emotion. The basal ganglia consist of the striatum (the caudate nucleus and the putamen together), the globus pallidus, the subthalamic nucleus, the substantia nigra, and the nucleus accumbens (the reward center). All three prefrontal circuits play a crucial role in the modulation of the thalamus via cortico-striato-thalamic projection fibers and the basal ganglia structures.

Below is the general organization of the frontal–thalamic (called cortico-striato-thalamic) circuits:
The thalamus, in turn, connects directly with the frontal cortex via the thalamocortical circuits, completing the loop between the frontal cortex and the thalamus. The common functional element of all the three prefrontal circuits is the modulation of the thalamus by the globus pallidus, both its internal and external parts (Burruss et al. 2000; Mega and Cummings 2001). The thalamic circuitry is tonically inhibited by direct fibers projecting from the internal portion of the globus pallidus (GP_i), a key structure of the basal ganglia. Other structures of the basal ganglia and the frontal cortex can reverse this default inhibition of the thalamus that is exerted by the globus pallidus. This select facilitation (reversal of inhibition) of the thalamus is transmitted through three different frontal–thalamic pathways (Feil et al. 2010): the direct (excitatory), the indirect (inhibitory), and the hyper-direct (inhibitory) pathway. The direct pathway disinhibits/stimulates the thalamus via connections that run through the striatum and GP_i. On the other hand, the indirect pathway inhibits the thalamus via connections that run through the striatum, the subthalamic nucleus, and the external segment of the globus pallidus (GP_e). The hyper-direct pathway is characterized by direct frontal input received by the subthalamic nucleus (bypassing the striatum), which sends excitatory output to the globus pallidus and the substantia nigra, resulting in the inhibition of the thalamus. In this model, the excitatory projections release the neurotransmitter glutamate and the inhibitory projections release gamma-aminobutyric acid (GABA). This information processing model is an example of one of the brain’s facilitative pathways. In a similar manner, the self-excitatory loops that sustain representations of interest in the brain can be selectively activated or facilitated.

Consider a real-life situation, in which someone mistakes a rope as a snake. In this circumstance, the cognitive uncertainties regarding whether it is really a rope or snake can cause autonomic arousal through the combined action of (1) the amygdala, which after receiving input regarding the danger from the thalamus rings the alarm that induces autonomic arousal, (2) the dorsolateral prefrontal cortex (DLPFC), which represents current cognitive contents including evaluative information concerning the dilemma (snake or rope), and (3) the cingulate gyrus, which generates autonomic tone and body movements consistent with the emotional contents of the situation (Critchley et al. 2003).

In evaluating a situation in order to determine the appropriate behavior, the brain uses the parallel information processing in which the cognitive and emotional centers process information simultaneously rather than sequentially. Because the transmission of information from the thalamus to amygdala is quicker than transmission from the thalamus to neocortex, emotional processing is often completed before cognitive evaluation (LeDoux 1996). The fast (thalamo-amygdalar) pathway activates an act first, think later mode of functioning, on the basis of associative fear memories stored in the amygdala. The slow (thalamo-neocortical) pathway reacts to a stimulus only after the structural dimensions of this stimulus are analyzed. In addition, as demonstrated in Fig. 3.1 below, unconscious emotional learning may be the result of a direct pathway from the thalamus to the amygdala, which does not involve the neocortex (Morris et al. 1998).

These mechanisms, because of their parallel presentations, may cause conflict among the prefrontal circuits when determining behavior. This can lead to emotional states that elicit approach or withdrawal followed by cognitive assessments that dictate contradictory behavior. The process of restoring balance and mediating the apparent conflict between circuitry and associated hyperarousal (caused by the thalamus and the amygdalar circuits) requires cognitive–emotional reappraisal of the dilemma (e.g., rope or snake) by the ACC and DLPFC. Only then can the individual determine the real situation. If reappraisal is successful, then knowledge-driven action can ensue (e.g., running away or attacking if the object is a snake or ignoring and moving on if it is a rope). While this imbalance appears greater in psychopathological states like depression, anxiety disorders, and addictive and personality disorders, harmonious integration of cognitive and emotional input is often not possible in the average individual’s daily life. Interestingly, in the meditative brain, the act first, think later functional mode is reversed, i.e., a meditative person is inclined to think first, act later. This reversal is likely due to modulations of the prefrontal cortex, anterior cingulated cortex, orbitofrontal cortex, and thalamic activity, in addition to the dampening of limbic–amygdalar hyperarousal. The actions of a meditative individual are governed by cognitive–affective balance rather than just emotions.

In cognitive neuroscience, the term salience refers to the qualities or properties of an item that stand out relative to the neighboring items within one’s field of awareness. Simply put, information’s salience is its pertinence or relative importance to that particular individual in that particular context within which the information was acquired. Salience plays a critical role in making our experiences unique, by means of selective attention and the activity of facilitative neural pathways involved in information processing. Salience affects how our experiences are encoded, organized, and stored in our brain for future use. Salience also plays a crucial role in potentiating a memory and, thus, converting short-term memory into long-term memory (i.e., consolidation). Within the context of incentive salience and the facilitated neural transmission of information, Berridge and Robinson (1998) propose an incentive salience hypothesis and elaborate on the role of dopamine, the pleasure chemical, in the reward and salience system. One significant finding within the large body of salience research (Schultz et al. 1997; Schultz 1998, 2002; Berridge and Robinson 1998, 2003; McClure et al. 2003) demonstrates that dopamine receptor antagonism does not manipulate the appetitive value of rewards, but instead selectively inhibits the initiation of reward-seeking behaviors.

Functional neuroimaging research points to the role of the insula and cingulate gyrus in the development of the (visceral) representations of our experiences. The insula plays a crucial role in processing the information that integrates interoception, the ability to perceive and respond to stimuli from one’s own body/organs (e.g., feeling one’s stomach rambling, timing one’s own heartbeat) with emotional salience. This integration generates a subjective representation of the body and bodily self-awareness like one’s sense of body ownership (Karnath et al. 2005). In addition to the insula and the cingulate gyrus, the orbitofrontal and amygdala assist in determining the salience of objects within our awareness by rating their emotional significance. The amygdala projects to the same sites in the orbitofrontal cortex that receive direct sensory input; this arrangement may allow the orbitofrontal cortex to extract the emotional significance of sensory events (Barbas et al. 2003). Both the amygdala and the orbitofrontal cortex ignore neutral sensory input, that which bears no implications of risk or reward, and function to cease response to any input lacking motivational value (Barbas et al. 2003). Thus, motivation plays a critical role in our experience of practice and learning like those of Yoga–meditation. When learning and practicing Yoga–meditation, the proper motivation can reinforce the experience via activity of the facilitative pathways. These pathways not only reinforce learning but also assist in maintaining representations of the experience within the brain, allowing one to own the experience.

The cognitive and emotional processes associated with meditative practices are mediated by interactions among the neural circuitry that govern our various experiences. Harmonious integration of cognition and emotions often is not an easy task even in the healthiest and normal individuals, and the imbalance is even greater in psychopathological processes. With recent advances in the cognitive neurosciences, these neural circuits provide us with answers for so many questions which were unanswered before. Research has demonstrated that the key brain areas in experiences like the meditative experience are the prefrontal circuit triad, thalamus, amygdala, hippocampus, and the basal ganglia system. In the meditative process, close interactions between these key brain areas, i.e., the prefrontal pyramid, thalamus, and amygdala, need more elaboration.

Scriptural descriptions of yogic philosophies often use the following terms interchangeably: true knowledge, direct experience, and Reality. The yogic philosophies claim pure knowledge or pure/direct experience provides the yogi (i.e., one who practices Yoga) access to the Reality of things based on the various levels of insights the yogi has obtained through meditation and from direct experience. Using a ladder analogy of insight, the yogi develops higher, more comprehensive views (insights) about the landscape (realities) when they climb atop the higher rungs of the ladder. Similarly, when one ascends the Empire State Building, their perspective of New York City becomes increasingly panoramic or holistic. The different levels of knowledge are equivalent to perceiving things from different levels of Reality. In yogic philosophies, pure knowledge, referred to as real knowledge or pure awareness, Truth, or wisdom, is obtained through insight that results from deeply contemplative practices like meditation. In meditative traditions, knowledge of the Reality (Sanskrit jnana; Pali nana, panna) is referred to as insight and forms the essence of mindfulness/insight meditation (vipassana in Buddhism or Samyama in Patanjali’s Yoga Sutras).