The Neuroanatomy of Opposites in Yoga Nidra
During the stage of opposites during yoga nidra, the practitioner generates a sensation from within, rather than reacting to sensations from the environment. This deepens pratyahara and strengthens the power of the witness, and the power of the will.
The practice of opposites in yoga nidra activates some of the most basic centers in the brain, the limbic system, which processes sensory information, taps into memory to make sense of the information, and relays that information to the higher parts of the brain for analysis, decision making, and action—all at lightning speed. The varied pairs of opposites often used in yoga nidra activate different portions of the limbic system. A link to a helpful interactive illustration is on page 30 of the SYN2 resource folder, and can also be found on the Web at https://www.newscientist.com/data/images/ns/sreport_flash/brain-interactive.swf
The thalamus processes signals from the peripheral nerves. There are distinct pathways for physically based opposites like hot/cold (temperature), heavy/light (position) and pain, and they activate different parts of the thalamus. The practice of these types of opposites helps train the practitioner to directly activate these centers, while at the same time engaging the witness (areas of the cortex) to observe rather than react to the information.
At first, one may need to engage memory to activate these sensations. Then, the activation area is the hippocampus, the memory processing center. Since communication is a two way street, some students practicing these opposites may find that certain memories come to mind during the practice.
The amygdala is where emotions are generated. Happy/sad, anger/peace, love/indifference, fear/courage all involve activating centers here. These are intermediate practice cues because the ability to witness must be well-established for students to remain engaged and benefit from the practice. Even seemingly mild cues from this group may elicit strong reactions from certain students. When they are well-prepared by prior experience in yoga nidra, this can be beneficial, but insufficient preparation may cause some students to have a negative reaction.
Great care must be taken when deciding to use opposites from this group for another, important reason. The amygdala is hyperactive in people with post traumatic stress disorder, or PTSD. People with PTSD have been found to have increased difficulty with deliberate regulation of emotion compared with people without this disorder. People with PTSD may not have identified this problem to the teacher, and may not even be aware of this issue themselves. While yoga nidra can be used therapeutically for PTSD, it should only be used by trained, experienced therapists who are also experienced in the practice and techniques of yoga nidra.
Finally, while looking at these anatomical correlations is useful, it is also important to remember that the yogic concepts of energetic and spiritual anatomy, including the chakras and the nadis, were derived from the meditative and reflective experiences of sages many centuries ago. Not every feature in yogic ‘anatomy’ may have a direct correlate in the brain and nervous system the way we understand it today, nor should we necessarily expect such correlations. There are decentralized aspects of the body’s intelligence, for example, the heart, the digestive system, and the immune system, which make ‘decisions’ without input from the central nervous system (CNS). At the same time, output from the CNS may affect those types of decisions, for example, the slowdown in digestive activity in the ‘fight or flight’ response, or the placebo response, when a medical condition improves in response to a sugar pill. Medical science has a long way to go in understanding all these phenomena.
The yogis of ancient times looked at corporeal existence as a whole, and then moved within, seeking the elemental components of the spiritual and energetic truths they had observed. On the other hand, modern medical science, from the time of the earliest dissections to today’s era of functional scans and molecular biology, operates more from the ‘let’s take it apart and see what makes it work’ approach. The intuitive insights and leaps of faith of the best scientists, those ‘out of the box’ moments which reshape our understanding in science and redirect our inquiries, are probably quite similar to the inquiry of those ancient sages, even though they approach investigation from completely different perspectives.