Zen and the brain: mutually illuminating topics

Abstract

Zen Buddhist meditative practices emphasize the long-term, mindful training of attention and awareness during one's ordinary daily-life activities, the shedding of egocentric behaviors, and the skillful application of one's innate compassionate resources of insight-wisdom toward others and oneself. This review focuses on how such a comprehensive approach to training the brain could relate to a distinctive flavor of Zen: its emphasis on direct experience, with special reference to those major acute states of awakening that create deep transformations of consciousness and behavior. In Japanese, these advanced states are called kensho and satori. Ten key concepts are reviewed. They begin by distinguishing between the concentrative and receptive forms of meditation, noticing the complementary ways that they each train our normal "top-down" and "bottom-up" modes of attentive processing. Additional concepts distinguish between our two major processing pathways. The self-centered, egocentric frame of reference processes information in relation to our body (our soma) or to our mental functions (our psyche). The other-centered frame of reference processes information anonymously. Its prefix, allo- simply means "other" in Greek. Subsequent concepts consider how these useful Greek words-ego/allo, soma/psyche-correlate with the normal functional anatomy of important thalamo ↔ cortical connections. A plausible model then envisions how a triggering stimulus that captures attention could prompt the reticular nucleus to release GABA; how its selective inhibition of the dorsal thalamus could then block both our higher somatic and psychic cortical functions; so as to: (a) delete the maladaptive aspects of selfhood, while also (b) releasing the direct, all-inclusive, globally-unified experience of other. Two final concepts consider how the long-term meditative training of intuitive functions relates to certain kinds of word-free spatial tasks that involve insightful creative problem-solving.

Keywords: Zen; allocentric; egocentric; meditation; thalamic model of enlightenment.

Figure 1

Egocentric and allocentric attentive processing; major differences in their efficiencies. This view contrasts our top–down dorsal egocentric networks with those other networks representing our ventral allocentric, bottom–up pathways. The reader's vantage point is from a position behind the left hemisphere, looking at the lower end of the occipital lobe. This person's brain is shown gazing up and off to the left into quadrants of scenery. The items here are imaginary. The baby and the hammer are within reach, in the space down close to the person's body. The scenery above and the tiger are off at a distance, out of reach. Starting at the top of the brain are the two modules of the dorsal, top–down attention system: the intraparietal sulcus (IPS) and the frontal eye field (FEF). They serve as the attentive vanguards linked with our subsequent sensory processing and goal-oriented executive behavior. Notice how they are overlapped by the upward trajectory of the upper parietal → frontal egocentric (E) system. This is a self-referential system. Its arching red pathway is shown as beginning in the upper occipital region. Notice that a similar red color also surrounds the lower visual quadrants containing the baby (at left) and the hammer (at right). Why? To indicate that this dorsal, “northern” attention system attends more efficiently—on a shorter path with a lesser “wiring cost”—to these lower visual quadrants. This enables our parietal lobe senses of touch and proprioception to “handle” easily such vitally important tangible items down close to our own body. In contrast, our two other modules for cortical attention reside lower down over the outside of the brain. They are the temporo-parietal junction (TPJ) and the regions of the inferior frontal cortex (IFC). During bottom–up attention, we activate these two modules of the ventral attention system chiefly on the right side of the brain. There, they can engage relatively easily the networks of allocentric processing nearby (A). The green color used to represent these lower temporal → frontal networks is also seen to surround the upper visual quadrants. Why? This is to suggest the ways this lower (“southern”) pathway is poised globally to use its two different specialized systems of pattern recognition. One is based on our sense of vision, the other on our sense of audition. Both serve not only to identify items off at a distance from our body but also to infuse them instantly with meaningful interpretations. The yellow FG in parenthesis points to this lower pathway's inclusion of the left fusiform gyrus. This region, hidden on the undersurface of the temporal lobe, contributes to complex visual associations, including our sense of colors.

Figure 2

Thalamocortical contributions to the dorsal egocentric and ventral allocentric processing streams. This composite view shows the pathways (normally bi-directional) which connect the thalamus with the cortex. For convenience in viewing, only left-sided structures are shown. These connections supply key regions both on the outside and inside of the left hemisphere. Pathways predominate from all five nuclei in the dorsal tier of thalamic nuclei. Up front are the three limbic nuclei. The medial dorsal (MD) thalamic nucleus projects to the prefrontal cortex, both to its medial (MPFC) and to its outer, dorsolateral (DLPFC) surfaces. The deep medial area of cortex in the back of the brain is shown enlarged at the top right. Here, the projections from the two other adjacent dorsal nuclei of the limbic thalamus can also be seen reaching this medial cortical surface (dashed lines). Thus, the anterior thalamic nucleus projects to the posterior cingulate cortex (PCC) (a major connection hub), and the lateral dorsal nucleus (LD) projects to the retrosplenial cortex (RETROSPLEN), a major memory-based resource for recollection. Down at the bottom right, one path leads up from the dorsal pulvinar (DPUL) to the angular gyrus (ANG) on the outer cortical surface. Dashed lines indicate that a second path from this dorsal pulvinar leads up to the precuneus (PRECUN) on the medial parietal surface. Other projections from the lateral posterior (LP) nucleus supply the superior parietal lobule (SPL), our major somatosensory association region. These connections help to anchor each person's subliminal sensory impression: I exist as an independent, tangible, physically-articulated body schema. Relatively few pathways are shown emerging from the thalamus to serve the lower, allocentric processing stream. However, messages from the ventral pulvinar (VPUL) would pass first through the region of the fusiform gyrus (FG) on the undersurface of the temporal lobe. These associations ramify, to become further refined on their way forward and upward through the other-referential networks in the rest of the temporal lobe that lead on toward the frontal lobe. The figure shows three important GABA inhibitory nuclei, artificially detached at the bottom. They are the reticular nucleus, the zona incerta (ZI), and the anterior pretectal nucleus (APT). Two sensory relay nuclei of the thalamus are also shown at the bottom right. The lateral geniculate nucleus (LG) relays visual data to the occipital cortex. The medial geniculate nucleus (MG) relays auditory information to the auditory cortex. The superior colliculus (SC) in the midbrain relays its reflexive visual and related polymodal messages quickly through both the dorsal and ventral pulvinar to the cortex. Its counterpart, the inferior colliculus, plays a similar auditory role. Not shown are two somatic sensory relay nuclei in the ventral tier. These medial and lateral divisions of the ventral posterior nucleus lie in front of the ventral pulvinar. They relay sensation from the head and body, respectively. cingulate gyrus (CG).