Many of the benefits of practicing yoga cannot be explained by modern Western science—especially the mystical aspects. Nevertheless, an advantage of approaching yoga scientifically is that we can often identify elements of the practice that produce a benefit and then use our knowledge of science to amplify the effect.
In today’s post we’ll take a look at the neuroscience behind the way the brain “sees” the body. Our video illustrates the “motor homunculus.” This is a visual map of the proportionate representation of the body in the brain. It is derived from the work of Dr. Wilder Penfield, a renowned Canadian neurosurgeon. He developed this map by stimulating regions of the brain in epileptic patients during surgery and then documented what parts of the body were affected. Dr. Penfield’s work was a pioneering contribution to medical science. It was original, elegant in its simplicity, and has stood the test of time.
Regions of the body requiring greater tactile skills and sensory awareness, such as the hands and tongue, have a correspondingly larger representation on the homunculus. Areas that are responsible for less complex activities are smaller on the map. Look at the psoas muscle, for example. Its representation is far smaller than that of the tip of the little finger!
What does all of this have to do with yoga? Well, it has been shown that the brain exhibits a quality known as “plasticity.” This refers to the body's ability to alter the physical structure and circuitry within the brain through specific types of training. Practicing yoga can be a method for accessing this malleability within the brain. For example, The Psoas Awakening Series can be used to expand the circuitry associated with this muscle.
From the time we first sit up (at around eight months of age), we use the psoas. In fact, we use it so regularly that the brain relegates it to the unconscious so that we don’t have to think about engaging it. Thinking takes energy, and the body is always looking for ways to conserve energy. Consequently, we “forget” how to activate this important postural muscle. For example, it’s easy to contract the biceps (just “make a muscle”). Try doing the same with your psoas.
Why is the psoas important? Let’s look at the origin and insertion of this muscle in Trikonasana. The psoas comprises two muscles—the psoas major and the iliacus. The psoas major originates from the T12 through L4 vertebral bodies, and the iliacus originates from the inside of the pelvis on the iliac fossa. Both muscles combine to form one tendon that inserts onto the lesser trochanter, a knob-like structure on the inside of the top of the femur (thigh bone). The psoas thus crosses multiple joints—it is polyarticular. This means that, when it contracts, it can affect the lumbar spine, pelvis, or hip. Its action is to flex the hip or trunk. The psoas is particularly important to incorporate into yoga since it confers core stability of the lumbar, pelvis, and hip in the poses.
So we go through the various phases of life: pre-school, adolescence, we fall in love, fall out of love—you get the picture. All the while the psoas is there, helping us sit up, stand, and walk. Then we start doing yoga. This takes the body into new and unaccustomed positions. And although many of the asanas would benefit from intentionally activating the psoas, it is rare that people can do so without first bringing it back under conscious control. You can do this by isolating this muscle in yoga poses. Once the brain perceives that you are engaging the psoas regularly during your practice, it will again relegate it to the unconscious, but with a new function: improving your yoga.
Be sure to click through to the Psoas Awakening Series and try it out. Think about how your homunculus changes during this important practice.
Thanks for checking in and we’ll see you for the next post when we go over joint reaction forces in yoga.
Ray and Chris