Proprioception II: A multi-keyboard performer
This is a follow-up to my previous post “Your Brain’s Miraculous Proprioception.” (https://medium.com/@vinlopresti/your-brains-miraculous-proprioception-you-wouldn-t-want-to-be-without-it-daf01758758).
Before my stroke, my two hands each had a mind of their own on a piano keyboard. This is neither analogy nor metaphor, but rather brain science.
Here, I discuss a proprioception example that hopefully extends and clarifies how remarkable is the brain’s ability to multitask. This example involves engaging one’s hands in separate but related precise movements such as those involved in simultaneously playing physically separated keyboards, one keyboard with each hand. Although they may be initiated by vision, once begun, such movements are not mostly visually directed, but instead involve the execution of motor programs facilitated by proprioception together with light-touch perception. I present this discussion in the context of a normal brain as contrasted with one that has sustained damage to its a proprioceptive and light-touch processing. It’s a deeply personalized perspective, in light of my own brain damage.
From Proprioception to “Tactile Stupidity”
Back in my 20s and 30s, I played keyboards in several bands. I located to the right of the stage. The keys were arranged at ninety degrees, a piano stacked with a Moog synthesizer in front of me, facing the audience, a Hammond Organ to my left, facing the rest of the band and angled about 90° from the piano/synth. Most songs, I played the organ with my left hand, the piano and synth with my right, although for solos on the organ, I’d swivel and play with one hand on each of its two keyboards. It’s those different-keyboard instances that demonstrate how damage to a piece of my sensory-processing brain (the post-Central gyrus of the Cerebral cortex) ablated my left hand’s ability to perform on its own keyboard, physically removed from my vision and my right hand performing several feet away on a different keyboard.
I’ve been pondering this for quite some time. Because of that brain damage, I lost both light touch and proprioception in my left hand and arm, but for years thought that it was a loss of pressure sensation in my fingertips that had to be the problem with that hand’s dexterity on a keyboard. Then I realized: no, it was mainly the proprioception loss.
Motor Programs and Their Proper Execution
To play my parts in each song the band performed, I repeatedly rehearsed them during band rehearsal, so that my fellow musicians knew what I was playing and vice-versa. During these rehearsals, I was also imprinting new motor programs that were ultimately stored in the motor areas of my brain, for our purposes, primarily the cerebellum. Although the cerebellum is the main repository for these motor programs, it must engage several other brain areas to execute them, including the primary motor (movement) cerebral cortex and basal ganglia. However, the primary sensory cortex is also critical because of its processing of proprioceptive input from the stretch receptors inside my muscles and joints — shoulders, elbows, wrists, hands, and each of the fingers. If undamaged, that sensory cortex “knows” where everything is in space, the important spaces here being those of the keyboards with respect to my body, arms, and hands. In addition to arm, wrist, and hand position, this includes the location/position of each finger with respect to the others on the same hand.
In simple terms, let’s picture the starting positions of my hands for a particular song, left hand on one of the organ keyboards to my left, right hand on the piano or synthesizer in front of me. At that moment, the precise positions of arms, hands, and fingers is known by my sensory cortex. It knows this because some muscles are active (contracted/shortened) while others are relaxed and stretched, this more/less stretch information informing my brain about those positions. For example, as I play chords or individual notes, the forearm muscles located on one aspect of my forearm (ventral, if you happen to know anatomy) are mostly shortening, those on the opposite (dorsal) side are generally being stretched. The opposite motions occur when I lift my fingers from the keys and move a hand to its next position in the motor program.
At the moment the song begins, I initiate the motor program from my cerebellum that primes my motor areas to implement the first sets of movements for each arm/wrist/hand. Right hemisphere controls left hand, left hemisphere controls right hand, each hemisphere aware of the other through information shared across the corpus callosum, the large bundle of nerve fibers that connects the right and left cerebral hemispheres. Those initial movements alter the arm and hand muscles, some muscles shortening others becoming stretched. (Of course, being more accurate, we’d have to specify how much shortening or stretching in each case). This proprioceptive information is processed by my sensory cortex.
Most importantly, that information is necessary to draw forth the next set of movements in the motor program. Assuming that this all is working well, each of my hands can and will move independently along each keyboard, playing its part as the motor program progresses through the song. Notice that I can use my vision at any point. But I generally don’t need to because it’s the ongoing proprioceptive feedback working with the motor program that makes these movements essentially automatic, mostly without visual guidance of my hands. Light touch feedback is also involved, but for simplicity, I’m focusing on the essential role of proprioception.
Unfortunately, since the damage to my right sensory cortex, the proprioceptive feedback from stretch receptors in my left arm, wrist and hand is not accurately processed by that damaged right hemisphere. My left hand no longer “knows” how to move among the different positions that place my hand and fingers in the correct sequence of playing positions because the motor program cannot properly execute without proper processing of the proprioceptive feedback from the muscles. This feedback changes from moment to moment as my performance proceeds through the song.
Since my brain damage, it turns out that even with both hands on the same keyboard, I can only play with my left by consciously choosing to visually direct it. Additionally, without proper processing of proprioceptive feedback from the stretch receptors, I can no longer form new motor programs for my left hand. That hand has therefore lost all automaticity. Moreover, even though I still have decent control of my left hand’s movements, my brain’s diminished proprioception is still relevant. For without the brain’s intimate knowledge of the position of the fingers and thumb of that hand with respect to one another, I still have difficulty making those fingers do what I’d like them to do, even using visual direction. Five fingers that once functioned almost autonomously now can’t seem to stay out of each other’s way.
I retain coarse movement ability; for example, the fingers will work together in wrapping themselves around an object and either carrying or twisting that object by clamping or moving in unison, but they cannot execute the finer relative movements in playing a keyboard. I point this out to illustrate that my problem is not being able to contract my forearm and hand muscles. But without healthy proprioception (and light touch perception), my muscles become instantly less useful. I’ve lost those fine movement skills in my left hand even though there’s no damage to either my muscles or by and large, to the motor areas of my brain.
Role for Inner Vision
Before my brain injury, I speculate that inner vision may have played some role. By that I mean an almost instantaneous internal imaging of where my hands should be on each keyboard, as though I were seeing them in a dream. Unfortunately since the damage to my right sensory cortex, without proprioception, inner vision is no longer of assistance to my left hand.
The brain is frequently a two-way street
The requirement for feedback to fine-tune brain activity is applicable to numerous other processes and such two-wayness can be thought of as fundamental to brain function, even for activities generally considered consciously initiated (voluntary).
